5th International Conference

Meetings - 5th Cormorant Conference (Freising)

last changed 16/01/02

5^th International Conference on Cormorants

2^nd Meeting of Wetlands International Cormorant Research Group

17 - 21 December 2000 - Freising, Germany

Abstracts

Cormorants in the Republic of Moldova

(Poster cancelled)

Bejenaru Ion ¹, Munteanu Andrei ², Balan Valeriu ¹
¹ Division of Biodiversity Conservation and Protected Areas Management, Ministry of
Environment and Territorial Development, Republic of Moldova, biodiver@mediu.moldova.md
² Zoological Institute, Academy of Science, Republic of Moldova

In the Republic of Moldova there are two Cormorant species: the Great Cormorant, Phalacrocorax carbo (Linnaeus), and the Pygmy Cormorant, Phalacrocorax pygmaeus (Pallas). For 80 years the Great Cormorant has been the more frequent species in the lower part of the river Nistru. Currently, however, both species are found in equal numbers in the Talmaza marshes (lower part of the river Nistru). With the construction of a fish farm on the river Drut near the city of Cahul, a high quality feeding site was created, and both Cormorant species increased in numbers. Generally, the two species live in separate colonies, though they do occur in one area in a mixed colony with Herons. For several years large numbers of Great Cormorants have been in the area, with 6,000 - 8,000 pairs estimated. However, with the cessation of work on the fish farm on the river Drut, numbers of Great Cormorants decreased considerably. When Great Cormorants were at their maximum numbers they caused great damage to the fish farm. Due to harassment actions to reduce numbers of Great Cormorants, birds frequently switched habitats. In more recent years the species was observed in the "Prutul de Jos" scientific reserve near the village of Slobozia Mare, Cahul district. Pygmy Cormorants reached a maximum number of 120 breeding pairs in the lower part of the Drut river, and are usually observed there with Great Cormorants. The Pygmy Cormorant is included in the Red Book of the Republic of Moldova and is listed as a Category IV IUCN protected species. Additional research is necessary for more detailed information.

SPATIAL DISTRIBUTION OF FEEDING CORMORANTS (Phalacrocorax carbo sinensis) IN THE COMACCHIO LAGOON (N ITALY)

(Poster Board # 15)

BOLDREGHINI PAOLO, FERRO ALESSANDRA, BON MARCO, MELEGA LUCA
Ist. Zootecnica, Università di Bologna, via S. Giacomo 9, I-40126 Bologna, Italy, boldreg@alma.unibo.it

Both feeding and resting Cormorants were counted monthly over a period of three years in a coastal lagoon located in the Southern Po River Delta. The entire area was divided into 24 sectors according to environmental features and current management. The use of each sector was estimated as either "importance" or as "density". In only a few cases, the sectors holding the higher proportions of birds also had the highest densities. A positive correlation was found between the mean densities of feeding and resting birds. The use of different sectors also varied seasonally.

DEVELOPMENT OF THE BREEDING POPULATION OF CORMORANTS PHALACROCORAX CARBO SINENSIS IN THE CORE AREAS OF NW EUROPE

(Oral Presentation # 01)

BREGNBALLE THOMAS* ¹, VAN EERDEN MENNOBART R. ², ENGSTRÖM HENRI ³,
KNIEF WILFRIED ⁴, KIECKBUSCH JAN J. ⁴, ESKILDSEN JÖRN
¹ NERI, Dept. of Coastal Zone Ecology, DK-8410 Rønde, Denmark, tb@dmu.dk,
² Rijkswaterstaat RIZA, P.O. Box 17, NL-8200 AA Lelystad, The Netherlands,
³ Evolutionary Biology Centre/Population Biology, Uppsala University, Norbyvägen 18D,
S-752 36 Uppsala, Sweden, ⁴ Landesamt für Natur und Umwelt Schleswig-Holstein,
Olshausenstrasse 40, D-24118 Kiel, Germany

About 130,000 pairs of the continental subspecies of the Great Cormorant (Phalacrocorax carbo sinensis) bred in Europe (excluding Ukraine) in 1995. Almost 70 % of these were bred in The Netherlands, Germany, Denmark and Sweden, i.e. in a former river delta and along the West Baltic coasts. We present information about the development of breeding numbers in these four countries where a transition from growth to stabilisation took place during the 1990s. The Dutch breeding population reached a maximum of ca. 21,000 breeding pairs in 1992. Since 1994, the Danish and German breeding populations have fluctuated around 38,000 and 15,000 pairs, respectively. However, the Swedish Cormorant population, now reaching more than 20,000 pairs, continues to increase, though now at a low rate. We discuss the importance of potential population limiting factors such as the availability of fish around existing colonies and human disturbance at hitherto uncolonised sites. We also discuss changes in the demographic features that seem to mediate the influence of external factors to determine local population trends. For example, does the external factor "food availability" limit breeding numbers because food availability in early spring sets a limit to the number of birds attempting to breed or because food availability during chick rearing greatly limits breeding output thus limiting the number of recruits?

DAILY fight for the best branch?

(Oral Presentation # 25)

Buchheim Andreas
Eichenstr. 1, 45711 Datteln, Germany

Continental Great Cormorants (Phalacrocorax carbo sinensis) congregate at communal roosts for the night. At Lake Hullern, a reservoir in Nordrhein-Westfalen, Germany, birds have chosen large trees on the lakeshore to spend the nights. During the course of the year this roost is used by short-staying (migrant) and long-staying (mostly over-wintering) individuals, thus presumably birds of different dominance-classes. It was suspected that adult Cormorants are dominant over younger individuals, and that males are dominant over females. By comparing the percentage of roosting adults in old and new parts of the roost from December to April this was checked (ageing was not possible in fall, sexing was only occasionally possible). Dominant birds should always try to select the best branches. With the aid of colour-ringed individuals I observed if daily fights occurred for the best branches, if there were age-related strategies in occupying branches, or if dominance was more closely related to the duration of a stay. Results are discussed.

Fishing behaviour of Cormorants in the Gulf of Gdansk (N Poland)

(Poster Board # 16)

BZOMA Szymon, GAWIOR Tomasz, STEMPNIEWICZ Lech
Department of Vertebrate Ecology & Zoology, University of Gdansk, Legionów 9,
80-441 Gdansk, Poland, bioszb@univ.gda.pl

Observations of feeding Cormorants (Phalacrocorax carbo) were made during spring and summer 2000 in two different sites of the Gulf of Gdansk: sandy bottomed coastal shallow water, 1 - 4 m deep, and at the harbour basin, 4 - 8 m deep. We measured duration of diving, fishing efficiency and duration of resting on the water surface. In the shallow coastal water mean duration of diving decreased from 44 sec. in February to 22 sec. in August. Duration of resting on the water surface was relatively stable (21 – 33 % of feeding duration). Efficiency of feeding increased from 3 % in February to 15 % in April and decreased to 8 % in August. In the harbour basin, fishing efficiency was significantly higher (15 - 18 % in May - August), and duration of successful dives was shorter
(12 – 49 %).

Seasonal changes in exploiting different feeding areas by Cormorants breeding at Katy Rybackie (N Poland)

(Oral Presentation # 10)

BZOMA Szymon*, GOC Michal, BRYLSKI Tomasz, STEMPNIEWICZ Lech
Department of Vertebrate Ecology & Zoology, University of Gdansk, Legionów 9, 80-441 Gdansk, Poland, bioszb@univ.gda.pl

The Great Cormorant (Phalacrocorax carbo sinensis) colony at Katy Rybackie (ca. 8.000 pairs) is located on the Vistula Spit, between the Gulf of Gdansk and the Vistula Lagoon (northern Poland). Birds from this colony use both water bodies as feeding areas. During two breeding seasons (February - August 1999 and 2000) we observed characteristic changes in the number of Cormorants flying to each feeding ground. Two methods to assess use of the feeding areas were utilized twice a month: Pellets were collected bi-monthly from different parts of the colony and assigned to either marine or lagoon origin on the basis of content (characteristic marine or lagoon species). Direct counts of all birds flying out and coming back to the colony from the two main directions, gulf and lagoon, were made. The correlation between the results obtained by these two methods was high: r = 0.90 (t = 5.32, p < 0.05) in 1999 and r = 0.91 (t = 6.37, p < 0.05) in 2000. In February and March Cormorants foraged mostly in the lagoon (80 - 100 % of feeding flights). Use of the Gulf feeding ground increased significantly to 60 - 70 % in May. In July - August it dropped again to 20 - 30 %. Pellet analysis showed that birds nesting in those parts of the colony closest to the lagoon were more likely to use that water body as a feeding ground.

Monitoring of daily food intake by cormorants: comparison between NESTLING regurgitationS and automatic weighing of nests

(Poster Board # 17)

Carpentier Alexandre, Marion Loïc
Université de Rennes 1, Laboratoire d’évolution des systèmes naturels modifiés, UMR Ecobio 6553, 35042 Rennes Cedex, France,
alexandre.carpentier@univ-rennes1.fr, loïc.marion@univ-rennes1.fr

Food needs of Cormorants are traditionally studied with different methods (pellets, regurgitated fish or stomach contents analysis, energetic models, studies of captive birds), however each has associated bias. In this 2-year study, we compared results from the sequence of adult feeding trips and nestling regurgitations in the nest with adult food delivery measured automatically by nest mass balances. The mean daily food intake varied according to brood size with a mean of 330 g per day for one young from the regurgitation study. Results from the automatic weighing showed similar results but allowed us to distinguish between adult consumption and the exact quantity of food delivered to the brood. The latter method also gave important information about daily variations in food consumption during the breeding period.

REDUCING THE CONFLICT BETWEEN CORMORANTS AND FISHERIES ON A PAN-EUROPEAN SCALE: REDCAFE OPENS FOR BUSINESS

(Oral Presentation # 29)

CARSS DAVID N.* ¹, BREGNBALLE THOMAS ², KELLER THOMAS M. ³,
VAN EERDEN MENNOBART R. ⁴
¹ Centre for Ecology & Hydrology Banchory, Hill of Brathens, Banchory, Aberdeenshire, Scotland, AB31 4BW, d.carss@ceh.ac.uk, ² Dept. of Coastal Zone Ecology, National Environmental Research Institute, Kalø, Grenåvej 12, Rønde, Denmark, tb@dmu.dk, ³ TU-München, Angewandte Zoologie, Alte Akademie 16, D-85350 Freising, Germany, t.keller@lrz.tum.de, ⁴ Institute for Inland Water Management & Waste Water Treatment (RIZA), Dept. of Wetland Development & Restoration,
P.O. Box 17, Zuiderwagenplein 2, Lelystad, The Netherlands, m.veerden@riza.rws.minvenw.nl

The purpose of the REDCAFE project is to synthesise current Cormorant/fisheries information and to identify and evaluate methods of reducing the current Europe-wide conflict between conservationists and fisheries interests. It will bring together, for the first time, stakeholders (commercial/recreational fisheries and bird conservation organisations, fisheries scientists and avian ecologists from over a dozen countries) to discuss and report these issues in a rigorous, co-ordinated and equitable manner. Available information on Cormorant conflicts with fisheries (with best estimates of financial losses) and on those aspects of Cormorant ecology leading to such conflicts, will be synthesised. Potential management tools will be identified and evaluated (including efficacy and cost-effectiveness) and a Multiple Criteria Decision Model will be developed and applied to a specific conflict case study. Full information will be disseminated at the local, national and European level. This overview is an introduction to this 2-year project recently funded under the European Union’s "Quality of Life and Management of Living Resources" Fifth Framework Programme.

ISSUES Of WINTERING GREAT CORMORANTS (Phalacrocorax carbo) at THE RAMSAR SITE OF HONG KONG

(Poster Board # 29 and # 30)

Chan J. K., Tsim S. T., So P. M.
Agriculture, Fisheries and Conservation Department, Hong Kong Special Administrative Region, China, wetland@afcd.gov.hk

The Mai Po Inner Deep Bay Ramsar Site (1,500 ha) in Hong Kong supports some 7,000 Great Cormorants in addition to other waterbirds. In the last few years, local fish farmers have become increasingly concerned that Cormorants are taking fish from commercial freshwater fish ponds. To address these concerns, the government met with the manager of the Mai Po Nature Reserve within the Ramsar Site and local fish farm representatives. A strategy was developed to minimize predation at commercial fish ponds during the wintering period (Nov – Mar) and includes the following measures: Tilapia (a relatively less marketable fish) are stocked in one of the ponds in the Mai Po Nature Reserve to enhance prey availability and attract Cormorants to this site, while simultaneously drawing them away from adjacent commercially operated fish ponds; low water levels are maintained in some ponds in the Nature Reserve to make them easier foraging grounds for Cormorants; and outside the Nature Reserve, government encouraged fish farmers to set up "grid lines" to reduce Cormorant predation in their ponds. The strategy has been implemented for three years but fish farmers are still very concerned about loss of production due to Cormorant predation at their ponds. A review is in progress to explore more effective measures to address concerns.

Long term effects of cormorant predation on fish communities
and fishery YIELDS in a freshwater lake

(Oral Presentation # 17)

Engström Henri
Evolutionary Biology Centre/Population Biology, Uppsala University, Norbyvägen 18D,
S-752 36 Uppsala, Sweden, henri.engstrom@ebc.uu.se

Cormorant impact on natural fish populations has long been debated but little studied because the requirements of rigorous data are often difficult to meet. In this study I monitored fish community composition/abundance before and after a Cormorant colony was established in a high productive lake, Ymsen, of South-central Sweden. Data on fish abundance before Cormorant establishment enabled me to control for changes in fish densities prior to Cormorant colonisation. To control for possible changes in fish populations caused by factors other than Cormorant predation (i.e. large-scale regional changes due to climate) data were compared with a control lake, Garnsviken, with no Cormorants. Since Lake Ymsen also supported an important commercial fishery, Cormorant impact on fishery yields was also evaluated. The most important fish species in the diet of the Cormorants were Ruffe, Roach and Perch. Except for Perch, commercially important fish made up a very small fraction of the Cormorant diet. Eel, the most important fish for the fishery, was rare in the Cormorant diet (0 - 0.2 %), Pikeperch constituted 0 - 0.2 % and Pike 1.5 - 2.9 %. Estimated fish outtake by the Cormorants was 12.8 kg/ha/year compared to 8.6 kg/ha/year for the fishery. Despite considerable fish consumption by the Cormorants, fish populations did not seem to change in numbers, biomass or size frequency distribution. The present study indicates that Cormorant impact on fish populations in Lake Ymsen was small and had probably not led to declines of either commercial or non-commercial fish species. Nevertheless, the number of breeding Cormorants in Lake Ymsen, in relation to foraging area (8 pairs/km²), is among the highest known for Swedish lakes.

HUMAN HARASSMENT AND CORMORANT NESTING AT FOUR COLONIES IN EASTERN LAKE ONTARIO, NEW YORK; OBSERVATIONS FROM A MANAGEMENT PROGRAM

(Poster Board # 32)

Farquhar James F., Mazzocchi Irene M.
New York State Department of Environmental Conservation, Watertown, NY 13601, USA, jffarquh.Watertown.REG60@gw.dec.state.ny.us

Since 1994, the New York State Department of Environmental Conservation (NYSDEC) has managed Double-crested Cormorants (DCC) Phalacrocorax auritus with the objective of preventing colony establishment on three eastern Lake Ontario island sites. This management was undertaken in response to concerns about competition with other colonial waterbirds and damage to private property. Techniques used have included frequent human visitation, deployment of scare devices, and nest destruction/removal. Initial nest numbers at the beginning of the season have varied from 0 - 1,235. One to five site visits per year have been effective in achieving the objective. In 1999, NYSDEC began managing a fourth eastern Lake Ontario island, which supported the largest DCC colony in New York State. The objective was to reduce fish consumption by suppressing Cormorant reproduction. This management practice was initiated following studies which linked high Cormorant populations to decreased Smallmouth Bass (Micropterus dolomieui) survival and abundance. In 1999 and 2000, all accessible Cormorant eggs (maximum 16,310 and 10,917 respectively) were sprayed with vegetable oil approximately every two weeks beginning in May and ending in late June. Five oiling sessions were sufficient to reduce chick production at this colony by more than 95 %. Cormorant nest numbers also decreased on this colony from 5,681 in 1999 to 5,119 in 2000. Five other species of colonial waterbirds nest on the four islands. Impacts of management activities on the abundance of other colonial species are discussed.

increasing confidence iN impact estimates – The monte carlo approach

(Oral Presentation # 15)

Feltham M.J. ¹, Davies J.M. ², Wilson B.R. ³, Holden T. ^4

1 School of Biological and Earth Sciences, Liverpool JMU, Byrom Street, Liverpool L3 3AF, UK, besmfelt@livjm.ac.uk, ² School for Professional and Continuing Education, University of Birmingham, Birmingham B15 2TT, j.m.davies@bham.ac.uk, ³ Environment Agency Wales, Penyfai House,
19 Penyfai Lane, Furnace, Llanelli SA15 4EL, UK, ben.wilson@environment-agency.gov.uk,
⁴74 Max Road, Liverpool L14 4BJ, UK

Estimates of depredation by Cormorants Phalacrocorax carbo at fisheries have been based largely on the intuitive equation Yi = n x c x pi, where n is the number of Cormorant days at a fishery, c is their daily food intake and pi is the proportion of species i in the diet. Yi is, therefore, an estimate of the mass of fish of species i likely to be removed by Cormorants from a defined area in a given time. The use of such equations, though relatively robust, has been criticised for two principal reasons. First, n, c and pi have usually been taken as constants and second, no confidence limits have been placed around the estimates of Yi. This has resulted in the erroneous impression that, for any particular fishery, there is a single impact figure. In an attempt to address these concerns we developed a Monte Carlo Simulation (MCS) programme which (i) accounts for temporal and spatial variation in Cormorant depredation and (ii) places meaningful confidence limits on estimates of impact. The methodology will be demonstrated using an inland fishery in England as a case study. The efficacy of using the MCS at other fisheries is discussed elsewhere at this conference.

estimating the impact of cormorants on inland fisheries - perfection or pragmatism?

(Oral Presentation # 16)

The impact of Cormorants Phalacrocorax carbo on a range of freshwater fisheries in England was examined between 1995 and 1998. The mass of fish removed by birds was related to angler catches and/or fisheries biomass using a Monte Carlo Simulation programme (see Feltham et al, this conference). The level of depredation at stillwaters was more variable than at rivers, consistent with the view that the latter may be better able to buffer against depredation than the former. High levels of impact at some sites (up to 57 % of fish biomass) did not, however, result in detectable reductions in fishery performance over the three years. This study suggests strongly that Cormorants are a specific, rather than general, problem for fisheries in England. Sufficient data are now available on how practical impact assessment can be undertaken on the case by case basis necessary to sensibly manage the potential conflict between Cormorants and fisheries.

MODELLING THE EFFECT OF WINTER CULLS ON CORMORANT POPULATION SIZE

(Oral Presentation # 33)

FREDERIKSEN MORTEN*, LEBRETON JEAN-DOMINIQUE,
BREGNBALLE THOMAS
CEFE/CNRS, Montpellier, France and NERI, Dept. of Coastal Zone Ecology, Rønde,
Denmark, mfr@dmu.dk

Culling in winter has been used as a management tool for Cormorants for at least the last ten years in several countries, with the highest relative intensity in France and Switzerland. However, no scientific evaluation of the effect of these culls has been carried out. We use mathematical modelling to try to evaluate whether culling can be considered an appropriate tool for management at various geographical scales. Recent information on Cormorant population processes (survival, recruitment and fecundity) is used in the model. Results show that the observed stabilization of breeding numbers in Northern Europe has probably been caused primarily by natural density-dependence, but also that culling in some circumstances can greatly influence population size. Culling at a local scale can have a strong effect if winter site fidelity is high, so that immigration into the site or region is limited. At the European scale, however, culls need to be both strong and widespread to be efficient. Model predictions could be strengthened by improved knowledge about natural density-dependence and site fidelity at the range-wide scale.

HOW MANY CORMORANTS USE AN AUTUMN STAGING SITE?

(Poster Board # 04)

FREDERIKSEN MORTEN*, BREGNBALLE THOMAS
NERI, Dept. of Coastal Zone, Ecology, Rønde, Denmark, mfr@dmu.dk

Information about how many Cormorants use a staging site is important for management of Cormorant conflicts; efforts at reducing local numbers will be less effective if the numbers present at any time represent only a small fraction of those that use the site. The best measure of the importance of a staging site is the volume, i.e. the total number of birds using the site during a migration season. If turnover of individuals is high, peak counts will severely underestimate volume. Resightings of colour-marked individuals can be used to estimate turnover through capture-recapture analysis. A recently developed method combines the results of such an analysis with count data in order to estimate volume. We illustrate this method using real-world data.

FOOD OF great cormorants Phalacrocorax carbo (L.), WINTERING AT
RESERVOIR POUTES, River ALLIER, France

(Oral Presentation # 11)

GERDEAUX DANIEL*, LELIEVRE MICKAEL
Station d’Hydrobiologie Lacustre, INRA, 74203 Thonon Cédex, France, gerdeaux@thonon.inra.fr

The reservoir Poutès is on the river Allier. Atlantic Salmon (Salmo salar) inhabit this river and a restoration plan is in progress. When smolts are migrating downstream during spring, Cormorants are still wintering at the reservoir. The present study examined the food remains in Cormorant pellets, collected weekly during spring 2000. The impact of Cormorant predation was not to be significant on the smolt population. The predation on Salmon occurs only during short periods. Cormorants continue to feed on Cyprinids and Percids even at times when smolts are in the reservoir. We discuss the reasons for such low predation on this important, but temporary, prey resource during 2000.

CHANGES IN NUMBER OF NESTS AND THEIR DISTRIBUTION IN THE
Great CORMORANT (Phalacrocorax carbo sinensis) COLONY
AT KATY RYBACKIE (N POLAND), 1995 – 2000

(Oral Presentation # 04)

GOC MICHAL
Department of Vertebrate Ecology and Zoology, University of Gdansk, Al. Legionów 9,
80-441 Gdañsk, Poland, biogoc@univ.gda.pl

The Great Cormorant colony is located in a mature pine forest. Number of breeding pairs has been monitored in the colony since the late 1950s, when ca. 100 pairs nested there. From 1995 to 2000 the number of pairs increased from 4,932 to 7,995, and the number of occupied trees from 2,404 to 3,495. The highest number of nests found on one tree was 19. Until 1997 the colony was compact, but recently its shape and range has changed; it has expanded to new parts of the forest and split into several subcolonies. Each season between 52 – 70 % of the occupied trees were those that had been used for nesting in previous years; the rest were newly colonised. Actual proportions differed significantly between seasons and between particular subcolonies, and depended on the growth rate of both the number of pairs and the area colonised, and on the number of trees cut down by foresters.

DAILY, SEASONAL AND INTERSEASONAL VARIATION IN THE FORAGING FLIGHT
TIMETABLE OF Great CORMORANTS (Phalacrocorax carbo sinensis)
AT KATY RYBACKIE (N POLAND)

(Poster Board # 18)

GOC MICHAL*, ILISZKO LECH, BRYLSKI TOMASZ, FILCEK JUSTYNA
Department of Vertebrate Ecology and Zoology, University of Gdansk, Al. Legionów 9,
80-441 Gdansk, Poland, biogoc@univ.gda.pl

During four breeding seasons (1995, 1996, 1999, and 2000) counts of birds flying out of and coming back to the colony were conducted. They were carried out from March to August, 3 - 4 times a month, from dawn to dusk. Daily number of foraging flights can be used in an estimation of actual consumption of fish by birds from the colony. Daily foraging rhythm was observed to change considerably during the breeding season, as well as the number of flights per day (5 - 45 thousands). There are two factors affecting these changes: the number of birds and their status (adult breeders, non-breeding "prospectors" and fledglings), and foraging activity. The latter differs among the status categories specified above; in the case of breeders, foraging activity depends on breeding stage. Examples of different daily activity patterns observed through behavioural studies carried out in the colony are presented and discussed. At the scale of colony and season, changes in flight numbers depended on synchronisation and timing of breeding and on proportion of non-breeding birds in the colony.

POPULATION DIFFERENTIATION IN THE GREAT CORMORANT
Phalacrocorax carbo IN EUROPE

(Poster Board # 05)

GOOSTREY A., CARSS DAVID N., NOBLE L. R., PIERTNEY STUART B.
Molecular Genetics in Ecology Initiative, Dept. of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, nhi680@abdn.ac.uk, and Centre for Ecology & Hydrology Banchory, Hill of Brathens, Banchory, Aberdeenshire, Scotland, AB31 4BW, d.carss@ceh.ac.uk

Individual Cormorants from 21 European populations were genotyped in order to (i) evaluate levels of pan-European population structuring and (ii) determine the genetic provenance of birds present in newly formed colonies in southeast England. Significant population differentiation was detected overall, with populations of the ‘North Atlantic’ (P. c. carbo) subspecies showing greater levels of divergence than populations of the ‘Eurasian’ (P. c. sinensis) subspecies. The population from southeast England clustered with P. c. sinensis populations in phylogenetic topologies, highlighting that this subspecies was present at these sites. Multivariate analyses indicated that these inland colonies were not comprised solely of P. c. sinensis but that both subspecies were living sympatrically and were probably hybridising at these English colonies. The implications for Cormorant management and conservation of P.c. sinensis breeding in the UK and of population introgression with P. c. carbo are considerable, and are discussed.

ENERGETIC BOTTLENECKS AND POPULATION DYNAMICS OF THE GREAT CORMORANT

(Oral Presentation # 21)

GRÉMILLET DAVID* ^1,
2, WANLESS SARAH ², LINTONDANI ^2

1Centre d'Ecologie et Physiologie Energétiques, CNRS, 23 rue Becquerel, F-67087 Strasbourg, France, david.gremillet@c-strasbourg.fr, ²NERC Centre for Ecology and Hydrology, Banchory Research Station, Hill of Brathens, Glassel, Banchory AB31 4BW, UK

Survival and reproductive success of individuals underpin the dynamics of animal populations. The European population of Great Cormorants (Phalacrocorax carbo) has increased rapidly over the last two decades. Although it appears that enhanced reproductive success explains this trend, the underlying ecological mechanisms remain unclear. We investigated this issue by studying the energetics of breeding, non-breeding and captive Great Cormorants exposed to variable environmental conditions (Western Europe and Greenland in summer and winter). We deployed nest-balances and VHF-transmitters to determine the feeding rates and foraging techniques of free-ranging birds. In addition, gas respirometry and stomach temperature loggers were used to study the energetics of adults diving in water at different temperatures and those of chicks of different ages. We identified two major energetic bottlenecks which may condition the dynamics of Great Cormorant populations: 1) fast-growing chicks require large amounts of food, 2) adult birds have abnormally high energy requirements when diving. We show that Great Cormorants respond to these major constraints by a set of behavioural adjustments which allow them to obtain food at rates unsurpassed by any other aquatic predator. Thus they minimise the time spent diving and maximise food provisioning to the brood. However, this particular strategy makes them dependant upon dense, highly profitable and predictable food resources occurring in warm water and at shallow depths. We discuss potential links between these results, the population dynamics of European Great Cormorants, the generalised eutrophication of fresh-water ecosystems, and the occurrence of these piscivorous birds at fish-farms.

CORMORANT HAZARD TO AVIATION

(Oral Presentation # 19)

HANSEN MOGENS
Copenhagen Airports A/S, Bird Strike Unit, Box 74, Lufthavnsboulevarden 6, DK-2770 Kastrup, Denmark, moha@tra.cph.dk

In September 1995, a U.S. Air Force 707 AWACS aircraft hit a flock of Canada Geese during takeoff at Elmendorf, Alaska. The aircraft crashed and all 24 crew members were killed. This was not an exceptional fatal accident caused by birds. In fact, birds are known to pose a serious hazard to aviation and these hazards are increasing. Furthermore, the material cost of bird strike damage to aircraft is enormous. Worldwide, total costs of bird strikes are estimated to be over 3 billion USD per year. As Canada Geese were involved in the fatal AWACS crash, Cormorants could lead to a similar accident to other aircraft. Perhaps, the flocking and flying behaviour of Cormorants poses an even more dangerous threat to civil aviation and to low flying military aircraft than does that of Canada Geese. Large flocks of Cormorants are found at several places in north-western Europe during most of the year. During the last four winters up to 10,000 Cormorants were attracted by an abundant food supply near Copenhagen Airport. Although no serious bird strikes involving these birds have occurred, they do pose a potential risk. Implementation of proper procedures against bird strikes involving Cormorants implies knowledge of important aspects of their behaviour and ecology. In practice, how can we design future research and apply subsequent results in order to minimize the conflict between Cormorants and aviation, and ultimatively to avoid loss of human lives?

USE OF NEST MATERIAL IN THE CORMORANT (PHALACROCORAX CARBO) BREEDING COLONY AT KATY RYBACKIE (N POLAND)

(Poster Board # 06)

ILISZKO LECH, GOC MICHAL
University of Gdansk, Dept. of Vertebrate Ecology and Zoology, Legionów 9, 80-441 Gdansk, Poland, biolil@univ.gda.pl

Cormorants use small pine (Pinus silvestris) branches and twigs with needles to build their nests. Depending on location, this material is transported from outside the colony as well as stripped from the trees on which nests are built. Cormorants lose some portion of these materials as they transport it to their nests. During the 2000 breeding season, dry mass of lost material was measured. All fresh branches with needles were collected from 10 study plots, and samples of the material were dried and weighed to estimate their dry mass. Mean dry mass [kg/nest/season] in the portions of the colony occupied for more than one year varied between 1.87 kg and 2.54 kg depending on plot location, while mean dry mass [kg/nest/season] in newly occupied portions was 10.55 kg. It was roughly estimated that the total dry mass of lost nest material in the colony area was not less than 25 tons. Temporal and seasonal changes in the mass of lost nest material and material used in nests is discussed.

PELLET PRODUCTION BY GREAT CORMORANTS (PHALACROCORAX CARBO) IN THE BREEDING COLONY AT KATY RYBACKIE (N POLAND)

(Poster Board # 19)

ILISZKO LECH, KOZLOWSKA KATARZYNA
University of Gdansk, Dept. of Vertebrate Ecology and Zoology, Legionów 9, 80-441 Gdansk, Poland, biolil@univ.gda.pl

The production of Cormorant pellets in the breeding colony (7,995 pairs) was studied during the 2000 breeding season. Pellets were counted and collected on 10 study plots (total area: 650 m²) every week. Samples were dried to estimate their dry mass (in total >7,000 pellets). The mean number of pellets/nest/day was 1.82. Dry mass of pellets varied between 0.3 and 12 g, with the mean mass of 2.1 g (n = 1,570). It is estimated that Cormorants produced at least 3.7 tons of dry mass pellets in the colony area. Seasonal and temporal changes in the mass and number of pellets, as well as the proportion of "empty" pellets in the total number produced are discussed.

PROBLEMS AT GREAT CORMORANT (PHALACROCORAX CARBO) COLONIES IN JAPAN

(Poster Board # 28)

ISHIDA AKIRA*, KAMEDA KAYOKO, NARUSUE MASAE
Aichi Prefectural Forest Research Institute, Kamiyoshida 43-1, Horai, Aichi 441-1622, Japan, HZH02144@nifty.ne.jp, Research Center, Wild Bird Society of Japan, 2-35-2 Minamidaira, Hino, Tokyo 191-0041, Japan, and Lake Biwa Museum, Oroshimo 1091, Kusatsu, Shiga 525-0001, Japan

In Japan, Great Cormorants establish colonies and roosts mainly in woods beside water. After the 1970s, the number of Great Cormorant colonies increased as the population increased. As a result, impacts to woodlands due to Cormorant droppings become serious in some places. Both Chikubu Island in Lake Biwa and Hama-rikyu Gardens in Tokyo are scenic areas, but colony expansion by Great Cormorants reduced their scenic value. On Chikubu Island various treatments were tried to dispel Cormorants but they had no effect. At Hama-rikyu Gardens, efforts have been more successful in protecting vegetation. At this site, a combination of two treatments has been utilized: string has been placed over the pond and a decoy has been placed at another site to attract Cormorants. Additional problems at Great Cormorant colonies in Japan and efforts to solve them are introduced here.

Recent TRENDS in numbers and DISTRIBUtion of Great Cormorant Phalacrocorax carbo in Wallonia (Southern Belgium)

(Poster Board # 02)

Jacob Jean-Paul ¹, Paquet Jean-Yves ^2

1 Centrale Ornithologique Aves and Observatoire Faune-Flore-Habitats de la Région Wallonne
² Centrale Ornithologique Aves, Rue de la Régence 36, B-4000 Liège, Belgium, jeanyves.paquet8@yucom.be, jean-yves.paquet@var.fgov.be

The Great Cormorant (Phalacrocorax carbo) was a rare visitor in Wallonia (Southern Belgium) until the eighties. A slow increase in numbers was followed by the foundation of the first colony ever in Wallonia in 1992. By 2000, two colonies were established, both in Hainaut Province, containing 180 - 200 pairs in total. In parallel, the species became a quite numerous migrant, with some Cormorants stopping-over in Wallonia, sometimes for several weeks, in the Meuse river or other suitable sites (e.g. extensive fishery-ponds). The regular wintering of Cormorants in Wallonia began in 1991. In the last three years, the wintering population has stabilised at around 3,000 individuals. The colonisation of the wintering area was progressive and has proceeded by successive steps. The Cormorants first colonised the lower part of the Meuse valley in 1991. After three winters, the entire Belgian part of the valley was occupied, and shortly afterwards some smaller tributaries had also night roost or visiting Cormorant parties during day-time. This situation stabilised in 1996 - 1997. Since then, a small number of Cormorants has extended their day-time range by exploring small ponds sometimes located at 20 - 25 km from the closest rivers.

THE POPULATION INCREASE OF THE GREAT CORMORANT (PHALACROCORAX CARBO) AND ITS DAMAGING EFFECT ON FISHERIES AND TREES IN JAPAN

(Poster Board # 27)

KAMEDA KAYOKO*, ISHIDA AKIRA, MATSUZAWA TOMONORI,
NARUSUE MASAE
Lake Biwa Museum, Oroshimo 1091, Kusatsu, Shiga 525-0001, Japan, kameda@lbm.go.jp, Aichi Prefectural Forest Research Institute, Kamiyoshida 43-1, Horai, Aichi 441-1622, Japan, Laboratory of Wildlife Biology, School of Agriculture and Life Sciences, Tokyo University, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan, and Research Center, Wild Bird Society of Japan, 2-35-2 Minamidaira, Hino, Tokyo 191-0041, Japan

We investigated the population increase and range expansion of the Great Cormorant (Phalacrocorax carbo hanedae) in three areas in Japan: Kanto, Tokai, and Kansai. Although the Cormorant had decreased in Japan in the 1970s, the population has increased since the 1980s, and a rapid increase was observed during 1990s. At the same time, the number of colonies has increased in the Kanto and Tokai areas. These changes have caused damage to fisheries and trees in each area. Most of the damage to fisheries is reported for fresh water species released for game fisheries, although the impact of Cormorants has not been assessed scientifically. Damage to forests and trees is reported at accessible places such as historic sites or parks in cities. We show one example of how people and Cormorants coexisted in the past in the Tokai area and suggest some future measures.

Cormorant Management in Bavaria, Southern Germany – Shooting as a Proper Management Tool?

(Oral Presentation # 34)

Keller Thomas M.
Technische Universität München, LG Angewandte Zoologie, Alte Akademie 16,
D-85350 Freising, Germany, t.keller@lrz.tum.de

Since autumn 1995 it has been legal to shoot Cormorants (Phalacrocorax carbo sinensis) in Bavaria to prevent anticipated economic damage and to protect native fish species. In the following winter of 1995/96, 657 Cormorants were shot. This figure increased to 6,259 birds in 1996/97 and then decreased to 3,285 in 1997/98 and 3,577 in 1998/99. Comparing these data to the mean winter population of Cormorants in Bavaria, showed that numbers equal to 50 – 100 % of the winter population were shot, each year. However, mean winter numbers of Cormorants did not decrease, substantially during this period. Thus, it could be argued that shooting Cormorants has not been an appropriate management tool to reduce overall depredation in Bavaria.

Cormorant Predation at Bavarian Lakes: Is there
a significant impact to local fisheries?

(Poster Board # 26)

Keller Thomas M.
Technische Universität München, LG Angewandte Zoologie, Alte Akademie 16,
D-85350 Freising, Germany, t.keller@lrz.tum.de

From December 1991 to November 1994 the numbers of Cormorants (Phalacrocorax carbo sinensis), their food and the development of the fishery yields where studied at three lakes in Bavaria, Southern Germany. Additionally, long term data on the commercial catches were analysed. Study sites comprised lakes Chiemsee and Ammersee, two large pre-alpine lakes, and lake Altmühlsee, a recently completed reservoir. Cormorants wintered on all three lakes and bred at lake Ammersee and at the reservoir. The main prey species recorded in 1,785 Cormorant pellets were Cyprinids. At the pre-alpine lakes Whitefish (Coregonus spp.) and Perch (Perca fluviatilis) were seasonally important food components, too. Overall, fishery yields at the study lakes showed vast fluctuations in the recent years. While Whitefish was the principal commercial fish species in the two pre-alpine lakes, Carp (Cyprinus carpio), Pikeperch (Stizostedion lucioperca) and Pike (Esox lucius) were most important to the anglers at the reservoir. No significant impacts on the yields of the commercial fisheries were found at the two large pre-alpine lakes, although catches were rather low due to reasons other than bird predation. At the reservoir high angling catches of Carp, Pikeperch and Perch were recorded despite the presence of high numbers of Cormorants.

AN UPDATED ASSESSMENT OF THE IMPACT OF CORMORANTS ON FISH STOCKS IN
LARGE PRE-ALPINE LAKES IN BAVARIA

(Oral Presentation # 18)

KLEIN MANFRED
Bayerische Landesanstalt für Fischerei, D-82319 Starnberg, Germany, manfred.klein@lfi.bayern.de

Between 1991 and 1994 a comprehensive study was carried out by the Bavarian State Institute for Fishery on the impact of Cormorants on fish stocks. The study focused on selected water bodies in Bavaria. Since then the pattern of distribution and presence of Cormorants throughout the year has changed. Furthermore, existing breeding colonies have increased and new ones have been established. At Lake Chiemsee (8,000 ha surface area) the impact of Cormorants was assessed by comparing the ratio of fish removed by Cormorants and by fishermen, respectively. The amount of Cormorant prey in relation to the catches of fisherman will provide information on the degree of competition. In this connection a central question has to be discussed: to what extent are fishermen expected to tolerate competition with Cormorants? During 1995 - 1998, compared to the total yields of commercial fishermen, Cormorant consumption was 30 to 50 % corresponding 2.5 to 4.2 kg/ha each year. If the fishery is to operate in a sustainable way, the removal of fish by Cormorants should not exceed 10 % of the total commercial yield. Regulation measures of the Cormorant population are recommended if their consumption is higher than this.

CHANGES IN THE BREEDING SUCCESS OF GREAT CORMORANTS (Phalacrocorax carbo sinensis) IN THE EXPANDING COLONY AT KATY RYBACKIE (N POLAND):
EFFECT OF PHENOLOGY AND AGE OF SUBCOLONY

(Poster Board # 07)

KOPCIEWICZ Piotr, OLSZEWSKA Agnieszka, NITECKI Czeslaw, STEMPNIEWICZ Lech
Department of Vertebrate Ecology & Zoology, University of Gdansk, Legionów 9, 80-441 Gdansk, Poland, biols@univ.gda.pl

Data were collected during six breeding seasons (1995 - 2000) in the largest Polish colony of Great Cormorants (Phalacrocorax carbo sinensis) at Katy Rybackie (ca 8,000 pairs). During the study period the colony split into several isolated subcolonies and translocated to unoccupied forest areas. Breeding success was measured in five sectors that were assigned following colony expansion in order to represent successive stages. Mean clutch size varied between 2.8 (1998, N = 30) to 4.1 (1999, N = 71) (range: 2 - 6). Hatching success was relatively high and varied from 80 % (1998, N = 44) to 87 % (2000, N = 114). Mean number of young fledged ranged from 1.1 (1998, N = 72) to 2.9 (2000, N = 75) per nesting attempt, and 1.5 (1998, N = 72) to 3.0 (2000, N = 117) at successful nests. Breeding success was significantly higher in the early nests and sectors compared with the late ones. During the first two years of colony expansion (1998 - 1999), reproductive parameters of Cormorants in the newly formed subcolonies (sectors no. 2 - 4) were significantly lower when compared to those of the original colony. However, the inverse situation occurred in the 2000 season due to changes in phenology (breeding occurred earlier in the new subcolonies).

THE CURRENT STATUS OF THE PYGMY CORMORANT (Phalacrocorax pygmeus) IN UKRAINE AND ITS PROTECTION

(Poster cancelled)

Korzyukov Anatoli, Korzyukov Oleg
Odessa State University, Dept. of Biology, Unit of Zoology, Shampansky per. 2,
65058 Odessa, Ukraine, olegk@te.net.ua

The Pygmy Cormorant is listed in the Red Book of Ukraine and ranked as an endangered species. In Ukraine it nests in three localised places: The Ukrainian part of the Danube delta, the Dniestr delta and northern part of the Crimea (Eastern Sivach). Breeding areas are concentrated in the Danube and Dniestr deltas. For instance, in the Danube delta in 1998, 730 pairs nested, and in 1999, 525 pairs bred (data of Zhmud M.E.). In 1985, 1995 and 1996, Pygmy Cormorants did not nest presumably because of environmental factors (during these years winters were severe). In the Dniestr delta in 1998, 260 pairs were marked during breeding, but because of river floods 46.1 % of nests perished (data of Rusev I.T.). For the first time we found Pygmy Cormorants breeding in the Dniestr delta in 1954 and we managed to ring several broods although birds may have nested here before. In our opinion, at that time numbers totalled no more than a few dozens. On eastern Sivach in 1996 no more than 15 - 20 pairs nested (data of Koshelev A.I.). The number of nesting pairs varies annually and depends on hydrological processes on the Danube, the Dniestr, and the course of spring development in the Ukrainian Black Sea coast. After the end of the breeding season, Pygmy Cormorants fly away to numerous Ukrainian regions situated to the North and to the East. Wintering birds can be observed quite often but numbers depend on the severity of the winter and formation of ice cover on the basins. For example, during January 1999 we recorded 123 birds in four places (Rusev, Korzyukov, Sacyk, 1999), and 301 birds in the Danube delta (Zhmud, 1999). In 1998 in the Danube delta 393 wintering birds were recorded (Zhmud, 1998). Analysing data from previous years, we conclude that the number of Pygmy Cormorants in Ukraine although stabilised is tending to increase and amounts to 700 – 1,000 pairs. At present an action plan for the protection of globally vulnerable bird species is being developed in Ukraine, and the Pygmy Cormorant is included in it.

ASSESSMENT OF THE NUMBER OF WINTERING CORMORANTS (Phalacrocorax carbo) IN THE SOUTH OF UKRAINE
(Poster cancelled)

Korzyukov Oleg, Korzyukov Anatoli
Odessa State University, Dept. of Biology, Unit of Zoology, Shampansky per. 2,
65058 Odessa, Ukraine, koroleg@yahoo.com

The Great Cormorant is a common breeder in the south of Ukraine, tending to increase in the last 5 - 10 years. Its main breeding areas are concentrated in the north-western part of the Ukrainian Black Sea coast, especially in the Danube and Dnister river deltas as well as on the islands of the Black Sea Biosphere Reserve. Large colonies also occur in Sivash and spits of the Azov Sea. Most of the breeding birds spend their winter on the south of the Balkan Peninsula and Italy. The birds breeding in Sivash also migrate eastwards to the Krasnadar region of Russia. The analysis of winter censuses shows that some adults winter in the southern Ukraine. For example, according to some authors (Rusev, Korzyukov, Satsyk, 1999; Zhmud et al. 1999) wintering birds concentrate locally in a few places. In 1999 in the Danube delta the local experts counted 450 Cormorants plus 83 individuals in the adjacent areas. In other areas, such as the south of the Crimea, there are only a few (i.e. tens of) birds. In total, there were 600 - 800 Cormorants in the south of Ukraine in 1999. In 1998 there were about 200 - 300 individuals. The number of Cormorants wintering in Ukraine depends on the severity of the winter and weather conditions on the south coast of the Ukrainian Black Sea. In severe winters (1984 - 1985) only a few birds are found in the area. In mild winters the number of Cormorants increases sharply to 900 – 1,000 individuals. Food resources are very sparse during this period, as shown from the stomach analyses of Cormorants. The increasing Cormorant population brings damage to fisheries and many fishpond owners cull birds. A lot of Cormorants also die in fishnets.

THE FACTORS DETERMINING DYNAMICS OF NUMBER OF GREAT CORMORANTS IN NORTHERN PRIAZOVIE

(Poster cancelled)

Koshelev Alexander I., Pokusa Roman V.
Melitopol Pedagogical University, Zoology and Ecology Faculty, 20 Lenin Street,
72312 Melitopol, Ukraine, mpi@comint.net

In Northern Priazovie nesting grounds of the Great Cormorant (Phalacrocorax carbo sinensis) have been under human control since 1980. All large colonies are located in nature reserves. We do mass ringing of adults, and take measurements on nests, layings and eggs. We have ringed more than 15,000 Cormorants and have received 150 ring returns. In the 1960s humans destroyed Cormorant colonies in this region in a special programme. At the beginning of the 1980s Cormorant numbers began to recover, and by the end of the 1980s, their numbers had increased. In the reservation on the Kuchuhyry Islands on the Kakhovka reservoir four Cormorant pairs nested in 1971. During these first years numbers were low, but increased at the beginning of the 1990s. Currently, Cormorant numbers are again low because of hunting. Cormorant nests are on high old trees in colonies with Ardea cinerea, Egretta alba, Egretta garzetta, Ardeola ralloides, and Nycticorax nycticorax. A colony with 100 - 250 nests was on the island of Zaporizhzhia, where there is a hydroelectric power station, in 1993 - 1995. In the "Obitochnaya Spit" reservation Cormorants have nested since 1984 (6 pairs) in a ground-nesting colony. The number of Cormorants increased and peaked in 1993 at 5,200 pairs. During 1994 - 2000, numbers of Cormorants have remained high at this site (1,160 - 3,200 pairs). In the Berdianskaya Spit Cormorants nested in large numbers (2,000 - 2,200 pairs) in 1992 – 1993, but after that their numbers decreased to 100 - 150 pairs. In the reservation on Molochny Bay Cormorants nested for the first time in 1988 (104 pairs); by 1990 the colony had reached 1,900 pairs. During the following years colony size ranged from 225 to 1,488 pairs. In general young birds take part in the formation of new colonies (75 - 90 % of population). We don't know why the proportion of older birds hasn’t increased, and it is not clear why so few of the birds that were ringed in previous years are present. The main factors causing Cormorant numbers to fluctuate in this region include: human persecution (destruction of colonies by fishermen, hunting, gathering of eggs and nestlings), poor food resources, unfavourable weather conditions (hurricanes, low temperatures), pressure from other species (Larus cachinans), and disease outbreaks.

WITHIN-COLONY VARIATION IN BREEDING SUCCESS IN A GREAT
CORMORANT COLONY IN DENMARK

(Oral Presentation # 06)

KRAG JENS SØREN M.*, BREGNBALLE THOMAS
Department of Zoology, Institute of Biology, Univ. of Aarhus, DK-8000 Aarhus C, Denmark, JSMKDK@hotmail.com, and National Environmental Research Institute, Dept. of Coastal Zone Ecology, Kalø, Grenåvej 12, DK-8410 Rønde, Denmark

The possibilities for correctly describing and interpreting year-to-year changes in colony breeding success rely on how representative the studied nests are for the colony as a whole. Thus, estimates of fledgling production will frequently be based on surveys covering only one or a few sections of a colony. The deviation of estimated total fledgling production from the real production of young can range from minor to major depending on the variation in breeding success within the colony. In the Danish Cormorant colony at Vorsø breeding success has been studied over a 20-year-period. Our data suggest that breeding success changed dramatically between 1991 and 2000. Between 90 and 350 nests have been surveyed each year, but they constitute only 2 – 30 % of all nests in the colony. It is therefore relevant to explore whether the observed changes in breeding success reflect changes in the colony as a whole or whether they are specific to the studied section of the colony. Our studies have therefore in recent years included other major sections of the colony and we present results of comparisons of breeding success among the studied colony sections. We test for variation in daily survival rate and use the Mayfield method and logistic regression to compare colony sections. We discuss likely causes for the observed within-colony variation, including effects of variation among colony sections in timing of breeding, age composition, and colony structure.

STUDY OF GREAT CORMORANT PHALACROCORAX CARBO POPULATIONS
BREEDING AND WINTERING IN GREECE

(Poster Board # 10)

LIORDOS VASILIOS*, GOUTNER VASSILIS
Department of Zoology, School of Biology, Aristotelian University of Thessaloniki,
GR-54006 Thessaloniki, Greece, acinonyx@otenet.gr, goutner@bio.auth.gr

In Europe, the Great Cormorant population has increased rapidly in recent years and its status has changed from threatened to thriving. The increase in numbers of this fish-eating species and its potential impact on the fisheries has drawn the attention of the public and scientific community alike. The purpose of this study is to provide needed information on the population size, growth, diet, and genetic identity of the Greek Great Cormorant populations. Research will be concentrated in the main breeding areas: the Axios and Evros Deltas, and Lakes Kerkini and Prespa, with the addition of the Messolonghi lagoon during the wintering season. Population data and information on eggs and clutch size are analysed and presented.

RECENT DEVELOPMENT OF POPULATION OF CORMORANT Phalacrocorax carbo IN FRANCE AND EFFECT OF SHOOTING ON ITS WINTERING DISTRIBUTION

(Oral Presentation # 03)

MARION LOÏC
Laboratoire d'Evolution des Systèmes Naturels & Modifiés, Université de Rennes 1,
35042 Rennes cedex, France, Loic.Marion@univ-rennes1.fr

France is an important wintering area for the North European Phalacrocorax carbo sinensis population. From the beginning of the 1980's increasing settlement occurred in new inland colonies, which represent now about 1,400 breeding pairs, while the coastal breeding population seems to have stabilised at about 1,900 pairs. However, the pioneering and main inland colony, Grand-Lieu, has also stabilised since 1997 after a decrease in 1996. In France, a management plan of shooting an increasing proportion of the wintering birds started in 1992 (from 5 % this year to 12 % in 1999) in an attempt to stabilise the wintering population. However, the total wintering population reached 83,000 birds in 1999, 10,000 more than in 1997 even if the annual rate of increase tended to decrease. Moreover, comparison between areas with and without shooting shows that shooting did not influence the distribution of birds. Such changes are probably due mainly to changes in resource use, with distributions extending into areas that were little used previously, while areas first used in the 1980-90's (large rivers) seem now to be saturated.

DIET COMPOSITION AND STOMACH ANALYSIS OF GREAT CORMORANTS (PHALACROCORAX CARBO SINENSIS) IN THE CZECH REPUBLIC

(Poster Board # 20)

Martincová Renáta* ¹, Musil Petr ^{1, 2

1}Department of Zoology, Faculty of Sciences, Charles University, Vinicný 7,
128 44 Praha, Czech Republic, mar_ren@hotmail.com,
²Institute of Applied Ecology, 281 63 Kostelec nad Cernými lesy, Czech Republic

Diet composition of the Great Cormorant (Phalacrocorax carbo sinensis) was investigated in the colony on the Ženich fishpond (Trebon Biosphere Reserve, South Bohemia) during the 1997 – 1999 breeding seasons. A total of 152 regurgitated fishes was collected. The most important fish appeared to be Carp (78.9 % of the food) and Tench (15.2 % of the food); Perch and Roach were found in minor percentages only. The length of fishes varied mostly between 12 - 20 cm. There was a significant difference between length of these two most frequently consumed species (ANOVA, F = 2.828, P < 0.01). Fish size increased during the breeding season (P < 0.001, r = 0.485). Since January 2000 stomach analyses of birds shot during the non-breeding period have also been carried out.

Diet composition of Cormorants (Phalacrocorax carbo sinensis) at
THE Katy Rybackie colony, northern Poland

(Poster Board # 21)

Martyniak Andrzej ¹, Wziatek Bogdan ¹, Szymanska Urszula ², Hliwa Piotr ², Terlecki Janusz ³
¹ Department of Fish Biology and Culture, University of Warmia – Mazury, Oczapowskiego 5,
10-957 Olsztyn, Poland, kbhr@uwm.edu.pl, ² Department of Environment Protection, University of Warmia – Mazury, Olsztyn, Poland, ³ Department of Evolutionary Genetics, University of Warmia – Mazury, Olsztyn, Poland, ⁴ Department of Zoology, University of Warmia – Mazury, Olsztyn, Poland

A study of the diet of Great Cormorants from the breeding colony at Katy Rybackie was carried out in 1996 - 1997. All materials were collected from March 1996 to September 1997. A total of 1,486 pellets (702 in 1996 and 784 in 1997) was found and analysed. Nineteen fish species were recorded in the pellets. Ruffe was the dominant species in the diet (70.5 % in 1996 and 75.5 % in 1997). Other important species included Roach (10.2 % and 5.3 %), Eelpout (4.0 % and 5.3 %) and Perch (3.5 % and 3.7 %). The percentage frequency of Eel was 0.4 % in 1996 and 1.2 % in 1997. In April 1996 the most important food item was Roach (53.2 %). Smelt was an important prey in March 1997 (17.1 %). Eelpout occurred in the diet from May to September and its proportion was highest in July (19.3 %). The mean length of each prey species consumed by Cormorants was: Ruffe – 8.1 cm; Smelt – 6.8 cm; Perch – 9.8 cm; Roach – 10.8 cm; Pikeperch – 18.5 cm; Eelpout – 19.2 cm; and Eel – 46.5 cm. In our opinion Cormorant predation is not having a significant impact on human interests in this area, because many of the fish species consumed by Cormorants have low market value in Poland. Additionally, Ruffe, which was the dominant fish species consumed by Cormorants, feeds on eggs of other important fish species and creates food competition in the Vistula Bay fish community.

THE LIMITATIONS OF PELLET ANALYSIS IN THE STUDY OF CORMORANT (Phalacrocorax spp.) DIET

(Oral Presentation # 08)

MCKAY HELEN V. ¹, ROBINSON KATHERINE A., CARSS DAVID N. ²,
PARROTT Dave* ¹
¹ Central Science Laboratory, Sand Hutton, York YO41 1LZ, UK, h.mckay@csl.gov.uk, d.parrott@csl.gov.uk, ² Institute of Terrestrial Ecology, Banchory, Kincardineshire,
AB31 4BY, UK, DNC@wpo.nerc.ac.uk

Analysis of bones in regurgitated pellets is a common method of inferring Cormorant diet. Twelve trial meals of Brown Trout (Salmo trutta fario) and Roach (Rutilus rutilus) of known sizes were fed to six captive Cormorants (Phalacrocorax carbo carbo) over a period of 36 days. A total of five pellets per day were produced by the six birds. Chewing pads, otoliths and pharyngeal jaws were extracted and used to estimate the weight, species and size of fish in the last meal. Results suggest that bone recovery is low and varies with fish size and species. Pellet analysis should therefore be used with caution, and supported by other techniques for assessing diet. The limitations of the method will be illustrated by describing its use in recent studies.

POPULATION TRENDS OF THE GREAT CORMORANT (PHALACROCORAX CARBO)
IN THE NORTH-EASTERN PART OF POLAND: 1993 – 1999

(Poster Board # 11)

Mellin Maria ¹, Mirowska-Ibron Iwona ^2

1 Wydzial Ochrony Srodowiska, Urzad Wojewódzki, ul. Pilsudskiego 7/9, 10-959 Olsztyn, Poland,
² Ul. Szczekin-Krotowa 11, 10-759 Olsztyn, Poland, norbi@sprint.com.pl

The first observation of Great Cormorants in the present Polish territory was made in the early 1940s. The first complete data for the breeding population was put together in 1973. In this year, there were 1,200 breeding pairs in 8 colonies in the country. The number of birds increased steadily through the 1980s, averaging between ca. 11 - 48 % annually. The following studies have been carried out in the north-eastern part of Poland. Breeding colonies: Regular monitoring has occurred at 21 breeding places in north-eastern Poland. After the destruction of three colonies in 1987, 17 had successful reproduction annually. Of these, five of the oldest are under legal protection. Inland, 2,231 nests were estimated at 16 colonies in 1999. In 1987, protests from fishermen prompted the first efforts to reduce the Cormorant population. Shooting was carried out in selected colonies and three colonies located near fish ponds were destroyed. After reduction in 1988, a decrease in the population was observed. Since the early 1990s, numerical changes have not been apparent, and in 1998 a maximum of 2,528 nests was estimated. In inland colonies, which have existed over 30 years, there are problems with spoiled tree stands. In five colonies 40 - 90 % of the trees have been destroyed. This forces Cormorants to build nests on bushes and on fallen trees. In these colonies, Rooks (Corvus frugilegus), Carrion Crows (Corvus corone) and White-tailed Eagles (Haliaeetus albicilla) cause reductions in numbers. Non-breeding colonies: Simultaneous with increases in the breeding population, increases in numbers of non-breeding birds were also observed. Non-breeders, which are not yet fully mature, don’t stay near breeding colonies; they occur in flocks and create non-breeding colonies. Since the early 1990s, non-breeding Cormorants have been roosting near lakes fairly distant from the breeding colonies. In 1997, 28 non-breeding colonies were recorded. In each colony, between 20 and 500 birds were observed. At a few of these colonies, attempts at building nests had begun. Reductions: At the present time, the Ministry of Environment and Province Nature Conservator control all legal Cormorant reductions. Since 1995, there has been an open hunting season for Cormorants in Poland in the fish farm areas after August 15. During the breeding season individual owners have been able to get permission to kill Cormorants.

Wintering GREAT Cormorants (PHALACROCORAX CARBO) in Prague

(Poster Board # 14)

Musil Petr^1,
2., Bergmann Pavel³, Martincová Renáta¹
¹ Department of Zoology, Faculty of Sciences, Charles University, Vinicná 7, Praha 2, CZ-128 44, Czech Republic, petr_musil@hotmail.com, ² Institute of Applied Ecology, Kostelec nad Cernými lesy, CZ-281 63, Czech Republic, ³ Uralská 6, Praha 6, CZ-16000, Czech Republic

The Vltava river in Prague (capital of the Czech Republic) has been an important waterfowl wintering site since the 1940s. Before 1990, numbers of wintering Cormorants did not reach 50 birds. Since then, numbers of wintering Cormorants have increased. In the second half of the 1990s, more than 1,200 birds were recorded. The highest numbers of wintering Cormorants were recorded in the days or weeks with the lowest temperatures, when other parts of the Vltava and Labe rivers were frozen in Central Bohemia outside of Prague. Cormorants are attracted by open water and good food supplies in Prague. In 1999 pellet analyses were begun to assess Cormorant diet at roosting sites in Prague. Recently, the Vltava river in Prague is one of the two most important Cormorant wintering sites on the territory of the Czech Republic.

Great Cormorants (Phalacrocorax carbo sinensis) in the Czech Republic: Numbers, distribution, current research and management plan

(Oral Presentation # 36)

MUSIL PETR*^1,
2, MARTINCOVÁ RENÁTA¹, CEPÁK JAROSLAV²
¹ Department of Zoology, Faculty of Sciences, Charles University, Vinicná 7, Praha 2, CZ-128 44, Czech Republic, petr_musil@hotmail.com, ² Institute of Applied Ecology,
Kostelec nad Cernými lesy, CZ-281 63, Czech Republic

Regular breeding of Great Cormorants has been documented in the territory of the Czech Republic since 1992. The breeding population increased until 1990. Since then, a remarkable decline and stabilisation, respectively, in numbers has been recorded. The decline in number of breeding pairs was caused by human regulation and diminished breeding opportunities. Recently, the population size reached about 180 - 200 breeding pairs in 3 - 4 colonies. However, thousands of birds migrate through the Czech Republic during both autumn and spring migrations. Breeding colonies are mostly located in the southern part of the country whereas larger concentrations of migrating birds are recorded in southern Bohemia, and in northern, central and southern Moravia. Therefore, an action plan for Great Cormorants in the territory of the Czech Republic was prepared in 1999. This action plan proposes full protection of the breeding population and allows flushing and/or shooting of Cormorants during the non-breeding season. Since 2000, Czech laws allow compensation for damages caused by Cormorants during the breeding season. Continued monitoring and more intensive investigations of Cormorant feeding ecology are recommended in the action plan.

ESTIMATING REPRODUCTIVE SUCCESS OF GREAT CORMORANTS PHALACROCORAX CARBO: THE RELIABILITY AND LIMITATIONS OF CURRENT METHODOLOGY

(Poster Board # 12)

NEWSON STUART E. ¹, BREGNBALLE THOMAS ²
¹ School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, United Kingdom, s.e.newson@bristol.ac.uk, ² National Environmental Research Institute, Department of Coastal Zone Ecology, Kalø, Grenåvej 12, DK-8410 Rønde, Denmark, tb@DMU.dk

Reliable estimates of reproductive success are fundamental to understanding the population dynamics of Great Cormorants. However, there is no consensus as to the most relevant parameters to monitor or information of the reliability or comparability of the estimates obtained. In most situations where a limited number of visits can be made to a colony, mean colony brood sizes are estimated from broods at different stages of development, often several weeks prior to fledging. Complete nestling failures can be missed and it is difficult to correct for partial or complete losses before or after observations are made. Although these are likely to inflate the apparent reproductive success, the level of inaccuracy is likely to vary between years and colonies, making correct interpretation difficult. In this paper we examine the reliability and limitations of current approaches to the collection, analysis and presentation of reproductive success data for Great Cormorants and discuss how standardisation could be improved without the need for increased monitoring effort.

YEAR-TO-YEAR SITE-FIDELITY OF WINTERING AND MIGRATING GREAT CORMORANT PHALACROCORAX CARBO IN THE BELGIAN MEUSE VALLEY

(Oral Presentation # 24)

PAQUET J.-Y.*, DERMIEN F., LACROIX P., LUCAS P., POURIGNAUX F.
Groupe de Travail Oiseaux Marqués, Centrale Ornithologique Aves, Rue Lucien Namèche 28,
B-5000 Namur, Belgium, jeanyves.paquet8@yucom.be

Every winter since 1991, about 2,000 Great Cormorants winter in the Belgian Meuse valley and gather at night in 9 different roosting places on riverine trees. Migrating Cormorant in stop-over ("short-stayers") are mixed with the wintering birds ("long-stayers"), mainly in October - November and February - March. During three consecutive winters, roosting places were checked for colour-ringed birds very regularly (at least on a weekly and sometimes on a daily basis). A total of 1,900 resightings of 93 different colour-ringed birds were obtained (30 birds originated from the Netherlands, 62 from Denmark and one from France). Year-to-year fidelity was examined at three levels: fidelity to the wintering or stop-over region (the Belgian Meuse valley), fidelity to the roosting place and fidelity to the position inside the roost. Long-stayer birds showed very strong site fidelity at the three levels: 92 % (n = 13) of long-stayer birds seen in 1997 - 1998 were present again in the Meuse valley the two next winters. Among these birds, 84 % stayed exactly in the same position inside the roosting place year after year. Although short-stayers had a lower fidelity rate, even taking into account their lower detectability, some of the non-wintering birds showed high fidelity to their roosting place from year to year, even for a short stop-over stays: 40 % of the short-stayers (n = 10) that were seen for more than two days in 1997 - 1998 were seen again during their stop-over the two next winters. Some observations of wintering Cormorants also indicated a high tendency for site fidelity to the fishing grounds.

CORMORANT-MONITORING IN LOWER AUSTRIA (1996/97 – 1999/2000) - Phenology, regional distribution and harassment actions

(Oral Presentation # 35)

PARZ-GOLLNER ROSEMARIE
Inst. für Wildbiologie und Jagdwirtschaft, Univ. f. Bodenkultur Wien, Peter Jordanstraße 76,
A-1190 Wien, Austria, parz@mail.boku.ac.at

Since the mid-eighties, the increasing number of migrating Cormorants, Phalacrocorax carbo sinensis, in Central Europe during the winter has resulted in severe conflicts between nature conservationists, ornithologists, fisheries interests and anglers in all Austrian provinces. Referring to article 9 of the determinations of the Council Directive 79/409/EEC on the Conservation of Wild Birds, the district government of Lower Austria issued time-limited regulations, which allowed the harassment and shooting of Cormorants along defined river sections, mainly focusing on the Trout and Grayling regions. An accompanying monitoring program was started including the following investigations and data collections: simultaneous roost counts to get basic information about the total number of migrating Cormorants, location of key roosting sites and main areas of regional distribution, survey and analysis of shooting reports, collection and investigation of shot Cormorants (including morphometric data, sample of birds), food analysis (stomach, intestinal contents) and the collection of pellets on two roosting places during the last winter period. To date, the effects of harassment actions during four winter seasons are described to document and evaluate the subsequent results of this action with respect to the abundance and actual distribution of the Cormorants.

POPULATION VARIATION IN THE FREQUENCY OF EXTRA-PAIR PATERNITY IN THE
GREAT CORMORANT Phalacrocorax carbo

(Oral Presentation # 23)

PIERTNEY STUART B., CARSS DAVID N.* & GOOSTREY A.
NERC Molecular Genetics in Ecology Initiative, Dept. of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, nhi570@abdn.ac.uk, and Centre for Ecology & Hydrology Banchory, Hill of Brathens, Banchory, Aberdeenshire, Scotland, AB31 4BW, d.carss@ceh.ac.uk

The frequency of extra-pair paternity (EPP) was examined in 8 populations of Great Cormorant (Phalacrocorax carbo) from NW Europe, by examining the allelic composition of broods at six unlinked hypervariable microsatellite loci. A number of broods (10/63; 16%) had allelic patterns inconsistent with the segregation of alleles from two parents. EPP was inferred in these cases. Considerable differences were observed between populations, with the frequency of EPP detected within broods ranging from 0 % to 40 %. Such variation was not attributable to underlying genetic diversity, nor colony density, factors that have been invoked for affecting EPP levels in other bird species. EPP is discussed in relation to the ‘reproductive status’ (i.e. increasing, stable or declining) of colonies.

GREAT CORMORANTS (Phalacrocorax carbo sinensis) WINTERING IN FRIULI - VENEZIA GIULIA: SPECIFIC AND QUANTITATIVE DIET COMPOSITION

(Poster Board # 22)

PRIVILEGGI NICOLETTA
Department of Biology, University of Trieste, Via Weiss 2, I-34100 Trieste, Italy, privileggi@miramare.it

To evaluate the Great Cormorants’ diet in Friuli - Venezia Giulia we chose two different roosts (Valle Cavanata and River Isonzo) with a large number of wintering birds. During a two year period, we analysed 1,036 pellets, collected monthly at the roosts. Remains of 9,808 prey comprising 39 fish species were identified. In Valle Cavanata the main diet components were Atherina boyeri, Platichthys flesus, Mugilidae, Gobidae and Cyprinidae. Economically important fish species, such as Dicentrarchus labrax and Sparus auratus, constituted only 11.5 % of the estimated biomass. Along the River Isonzo we found a high percentage of Leuciscus cephalus, Chondrostoma nasus, Salmonidae and Lepomis gibbosus. The daily food intake of Cormorants was estimated at 450 g in Valle Cavanata and in 350 g along the River Isonzo. We compare the diet in two distinct foraging areas and evaluate the relative abundance, the frequency of prey and the biomass of all ingested fishes.

ORIGIN AND MIGRATION PATTERN OF CORMORANTS (PHALACROCORAX CARBO) MIGRATING THROUGH OR WINTERING IN THE UPPER RHINE AREA
BY A COLOUR RING ANALYSIS

(Oral Presentation # 26)

RETTER MATTHIAS
Universität Freiburg, retterm@uni-freiburg.de
(home: A.-Strübe-Str. 4, D-79689 Maulburg, Germany)

The upper Rhine area from Schaffhausen (Switzerland) downstream via Basel (Switzerland) and Strasbourg (France) to Karlsruhe (Germany) is a very important area for wintering Cormorants (Phalacrocorax carbo) in Central Europe. Also, many Cormorants pass through the region on their route further south. An analysis of 391 resightings of mostly colour ring marked birds, comprising 143 individuals, was done for the region between 1983 and 2000. The majority of the birds was Danish. The rest were Dutch and Swedish, plus some other records of P. c. sinensis. A closer view at the recovery rate shows an insignificant difference between numbers of Dutch and Danish birds (Chi² = 0.205; p = 0.95). According to this, and comparing data from eastern and western longitudes, the same axial migration pattern as shown for Switzerland (Reymond & Zuchuat 1995) was shown for southern Germany and eastern France. However, in spite of approximately similar longitude, the ratio Dutch : Danish birds for two roosts was higher than that from Lake Geneva or Lake of Neuchâtel in Switzerland. This difference derives from examining Danish as well as Dutch ringing activities during the study period. Dutch birds are more important than previously assumed. Five Danish Cormorants were resighted in the Netherlands, migrating to the upper Rhine area. The importance of the river Rhine as natural migratory pathway was not confirmed by the data. Some of the birds which pass through the area winter in northern Italy or southern France. Finally, local migration and Perch fidelity is mentioned.

STATUS AND TRENDS IN GREAT CORMORANT POPULATIONS
IN NORWAY AND THE BARENTS SEA

(Oral Presentation # 05)

RØV NILS*, LORENTSEN SVEIN-HÅKON, PANEVA TATYANA
Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway. nils.rov@ninatrd.ninaniku.no, and Kandalaksha State Nature Reserve, Kandalaksha-2, 35, Lineynaya st., Murmansk Region, 184040, Russia

18,000 pairs of Great Cormorants Phalacrocorax carbo carbo breed on the coast of Central Norway. At the Barents Sea, including Norwegian, Kola and White Sea coasts, 8,000 pairs are currently breeding. Although there is considerable annual variation, an overall population increase has been recorded during the last 15 - 20 years. In Norway, positive annual changes of 4 % – 10 % have been found in most areas.

MULTI-DISCIPLINARY ANALYSIS OF CORMORANT CARCASES

(Oral Presentation # 22)

RUSSELL IAN C.*¹, BEARHOP STUART ², NEWSON STUART E. ³,
WINNEY BRUCE ⁴, ALLCHIN COLIN R. ⁵, KIRK RUTH S. ⁶
¹CEFAS, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK. i.c.russell@cefas.co.uk, ² Dept. of Biological Sciences, University of Durham, South Road, Durham DH1 3LE, UK, ³ School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK, ⁴ Genetics Dept., Queens Medical Centre, University of Nottingham, Nottingham, UK, ⁵ CEFAS, Burnham Laboratory, Remembrance Avenue, Burnham on Crouch, Essex CM0 8HA, UK, ⁶ Crucian UK, PO Box 1051, Kingston upon Thames, Surrey KT2 5WX, UK

In England and Wales, licences permitting the shooting of limited numbers of Cormorants (Phalacrocorax carbo L.) and other piscivorous birds, as an aid to scaring, require that bird carcases are retained for post-mortem examination. The main objective of these examinations is to provide information on the diet of birds at particular fisheries as a basis for future management advice. However, the carcases are also used in a range of other scientific investigations on Cormorant biology: Stable isotope analysis of wing feathers has been used to indicate the extent of freshwater feeding (over recent months) of Cormorants shot at inland fisheries. Morphometric measurements have been used to produce a discriminant function for distinguishing the two Cormorant sub-species (P. c. carbo and P. c. sinensis) and as a basis for estimating the relative proportions of the two sub-species among the birds shot under licence in England and Wales each year. Feathers and other tissues have been supplied for investigations of genetic variability in UK Cormorant populations. Cormorant livers have been analysed to assess the levels of polybrominated diphenyl ethers (PBDEs), in an effort to assess the extent to which these stable and persistent environmental contaminants are bioaccumulated by top predators such as the Cormorant. In addition, preliminary studies have been carried out to investigate the macrohelminth parasite communities in the intestinal tract of Cormorants. This paper aims to draw together and summarise the main findings of these various studies.

STOMACH CONTENTS ANALYSIS OF CORMORANTS AT DIFFERENT TYPES OF
FISHERIES IN ENGLAND AND WALES

(Poster Board # 23)

RUSSELL IAN C.*, COOK ALASTAIR, KINSMAN DANIEL A., IVES MARK J., LOWER NICOLA J.
CEFAS, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK, i.c.russell@cefas.co.uk

In England and Wales licences to shoot piscivorous birds can be issued where these birds are considered to be causing serious damage to a fishery. However, licences only allow limited numbers of birds to be killed in order to reinforce the effects of other scaring methods also being carried out at the site. A condition of all licences is that any shot birds should be frozen and retained to allow post mortem examination, in particular, to enable information to be collected on the prey species being consumed at particular sites. Detailed stomach analysis is subsequently carried out by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS). Overall results conform with the view that Cormorants are opportunistic predators consuming a wide range of available fish species and sizes. However, marked differences in diet are observed between different fishery sites, believed to be primarily related to prey availability and abundance. The paper reports on the prey composition of Cormorants feeding in different river catchments, and within an individual catchment. Comparisons are also made between the diet of birds feeding at stillwater put-and-take Trout fisheries with those feeding at stillwater coarse (predominantly Cyprinid) fisheries. The results are discussed in relation to economic considerations and the potential management implications.

THE USE OF CODED WIRE MICROTAGS TO ASSESS PREY SELECTIVITY AND
FORAGING BEHAVIOUR IN CORMORANTS

(Oral Presentation # 13)

RUSSELL IAN C.*¹, KINSMAN DANIEL A. ¹, IVES MARK J. ¹, FINNEY JASON ²,
MURRELL MARTIN ³
¹ CEFAS, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK. i.c.russell@cefas.co.uk, ² Central Science Laboratory, Sand Hutton, York YO4 1LZ, UK, ³ Environment Agency, Southern Region, Culverdene Court, Wessex Business Park, Wessex Way, Colden Common, Winchester, Hampshire SO21 1WP, UK

There are a number of inherent difficulties associated with quantifying the food consumption of Cormorants, especially where this relates to prey selectivity and assessing levels of predation upon commercially important fish stocks. One possible way of addressing this problem is the use of coded wire microtags. These miniature wire tags (~1.1 mm in length) are implanted internally into fish and can be applied to a wide range of species. The tags are quick and easy to apply, relatively cheap and are routinely used to tag large numbers of fish for population studies. The recovery and identification of tags from Cormorant pellets permits estimation of prey selectivity between different groups of tagged fish. Application of this technique requires that the likelihood of a tag being recovered from a pellet is not subject to inherent bias due to the species or sizes of fish that are tagged. Trials with captive Cormorants, fed with three species of fish, resulted in an overall tag recovery rate of 34.6 %. The tag recovery rates for Salmon parr (range 5.2 – 11.2 cm), Roach (range 5.6 – 21.7 cm) and Rainbow Trout (range 17.2 – 36.0 cm) varied between 30.4 % and 40.6 %, but were not significantly different at the 95 % level. Further, the tag recovery rates from the pellets for individual species were not related to fish length. A preliminary field trial on the River Test, southern England, following a Salmon stocking programme, resulted in the recovery of over 100 microtags from beneath Cormorant roosts. This technique thus appears to offer potential for investigating prey selectivity and Cormorant foraging behaviour in the field.

Recent development of the Cormorant Phalacrocorax carbo breeding population in Belarus

(Poster cancelled)

SAMUSENKO IRINA
Institute of Zoology NASB, Academichnaya Str. 27, 220072 Minsk, Belarus, ring@biobel.bas-net.by

Since the late of 1980s (first breeding registrations) numbers of Great Cormorant, Phalacrocorax carbo, have increased significantly in Belarus. A variety of problems with fisheries coincided with this increase. At present 10 breeding colonies are known, consisting of 1,120 – 1,250 breeding pairs/nests, but a few more small colonies probably exist. The Belarusian population was estimated to be about 1,300-1,500 breeding pairs in 2000. Breeding numbers continued to increase during recent years but the rate of increase has declined, especially for large (more than 100 nests) colonies. Most of the known Belarusian population (more than 70 %) is concentrated in 3 large colonies, the largest holding about 450 - 550 pairs in 2000. The number of Cormorants and colonies in selected years between 1988 and 2000 are discussed.

THE CONFLICTS BETWEEN GREAT CORMORANT AND FISH FARM PRODUCTION ON CARP PONDS - ATTEMPTED RESOLUTION AND STRATEGY IN SAXONY, GERMANY

(Oral Presentation # 32)

SEICHE KAREEN
Elbstrasse 8, D-01259 Dresden, Germany, Kareen.Seiche@t-online.de

In Saxony Cormorants appear during autumn migration and more than 90 % are in Carp pond areas. These Carp pond areas belong to the most important cultural landscapes in Saxony. Research studies in selected Carp ponds suggests that Cormorants could be responsible for serious economic damage. To prevent greater damage, shooting licenses are given out and several defence methods are used (e.g. fire arm, Razzo-Triplex, laser gun). Another method to reduce damage is to offer free feeding sites. For fishermen there are various possibilities for financial assistance. One is for especially high Cormorant damage, if economical livelihood is threatened. Damage is calculated by using pond economic data and with the help of field observation and a monitoring program.

RESOLVING THE CONFLICT BETWEEN GREAT CORMORANTS AND FISHERY IN ISRAEL

(Oral Presentation # 31)

SHY EYAL¹, GEVA AMITAI²
¹ Science Division, Nature and National Parks Protection Authority, 3 Am Ve’Olamo St.,
Jerusalem 95463, Israel, eyal.shy@nature-parks.org.il,
² Department of Fishery, Ministry of Agriculture, Tel Aviv, Israel

During the 1990’s, wintering Great Cormorant Phalacrocorax carbo sinensis numbers have increased to 20,000 individuals and damage to aquaculture has increased accordingly. The purposes of this project, conducted jointly by the NNPPA and the fishermen, were to study the movements and feeding behaviour of the Cormorants, to evaluate and improve means to deter Cormorants from fishponds, and to study alternative feeding grounds for Cormorants. Four major roosting Cormorant colonies fed in four fishpond areas and in Lake Kinneret. There was no correlation between fishpond area and the number of feeding Cormorants due to differences in the efficiency of deterrence between areas. A network of teams of local fishermen using noise explosives and other deterrence methods, guided in real time by an area patrol which monitored Cormorant movements between localities, proved to be highly efficient in eliminating damage to fishponds. Of two major alternative feeding grounds, Cormorants fed mainly in Lake Kinneret, and there was almost no feeding in the Mediterranean Sea. Cormorants feeding in the lake increased their body weight throughout the season, and there was a significant correlation between stomach fish weight and Cormorant body size. Their food consisted mainly of the small non-commercial fish Mirogrex t. terraesanctae. (This fish is removed annually to improve the water quality of the lake.). We conclude that the conflict between Cormorants and aquaculture may be resolved by deterring Cormorants efficiently from fishponds and driving them to feed mainly in Lake Kinneret, which can support them. We suggest that these Cormorants may indirectly improve water quality at the lake, which is the main water source of Israel.

INTERRELATIONSHIPS BETWEEN RUFFE (Gymnocephalus cernuus) AND CORMORANT (Phalacrocorax carbo sinensis) IN THE VISTULA LAGOON, N POLAND

(Oral Presentation # 12)

STEMPNIEWICZ LECH^*
1, MARTYNIAK ANDRZEJ ², BOROWSKI WLADYSLAW ^3

1Department of Vertebrate Ecology & Zoology, University of Gdansk, Legionów 9, 80-441 Gdansk, Poland, biols@univ.gda.pl, ² Olsztyn University of Agriculture and Technology, Oczapowskiego 5,
10-957 Olsztyn, Poland, ³ Sea Fishery Institute, Kollataja 1, 81-322 Gdynia, Poland

Ruffe (Gymnocephalus cernuus) is the most common fish species (22 - 29 % in sample catches) and constitutes the main component of Cormorant diet in the Vistula Lagoon (58 - 75 %). During one season fishermen caught ca. 272 - 548 t of Ruffe (bycatch) and Cormorants took ca 524 - 586 t. The most intensive predation took place in June when the number of birds and their total energy requirements were the highest. During three years of study (1995, 1996 and 1997) Ruffe proportions in sample catches (22.3, 29.0 and 28.0 %, respectively), in Cormorant diet (58.0, 70.5 and 75.5 %, respectively), as well as Ruffe biomass consumed yearly by Cormorants (524, 580 and 586 t, respectively), tended to increase. Very intense pressure exerted by Cormorants and fishermen on the Ruffe population in the Vistula Lagoon (in total ca. 800 - 1100 t/year) appears to have caused this population to approach its reproductive potential. Although proportions of Ruffe in the lagoon fish community were not observed to be decreasing, the age structure of the Ruffe population was influenced considerably. In the successive years of the study period younger and younger age classes dominated in the Ruffe control catches. Cormorants selected smaller Ruffe than were available in the lagoon (mean length: 11.0 cm in catches, 7.3 - 8.1 cm in pellets, 7.2 - 8.3 cm in fish regurgitated at colony). Most probably, environmental and anthropogenic factors are responsible for the continuing high proportion of Ruffe in the Vistula Lagoon fish community.

UNDERWATER VISUAL ACUITY IN THE GREAT CORMORANT

(Oral Presentation # 27)

Strod T.* ¹, Izhaki I.², Katzir G.², Arad, Z.^1

1Department of Biology, Technion-Israeli Institute of Technology, Haifa 32000, Israel, zarad@techunix.technion.ac.il, ²Department of Biology, University of Haifa at Oranim, Qiryat Tivon 36006, Israel

Great Cormorants (Phalacrocorax carbo sinensis) forage underwater for fish by pursuit diving and are considered as a major pest to fisheries. We have shown previously that Cormorants rely on vision for prey detection (unpublished). Yet, their visual capacities have not been investigated so far. This study aims to determine the visual acuity of Cormorants, diving in clear water. Five Cormorants were hand-reared in an aviary with a water tank, and fed on dead and live Carps (Cyprinus carpio) and St. Peter's fish (Tylapia spp.). The birds could dive in an underwater experimental set-up, including an Y-shaped mesh tunnel, with a prey box at either end. The maximal distance for prey detection was determined by presenting a fish in the prey boxes behind transparent doors. In clear water (0.2 - 0.3 ntu), 4 of the tested Cormorants were able to detect 3 cm long fish (Tylapia) from 3.6 m and more, suggesting a minimal angle of resolution (MAR) of 29 minutes of arc or less. The Cormorant’s visual acuity was further tested, using two stimuli of black-white gratings of equal cycle but of perpendicular orientations. The birds were rewarded only after choosing the vertical grating side. In clear water, the Cormorant’s MAR is 16` - 18.2` (3.1` - 3.75` cycles/degree). The MAR of horizontal grating (16` - 18.2`) was 2.2` - 6.5` less than that of vertical grating (20.4` - 22.5`), indicating a higher sensitivity to horizontal elements. Underwater visual acuity in the Great Cormorant is thus slightly better than known in most diving mammals and poorer than known in most fishes (* Supported by the Israeli Ministry of Science).

TURBID OR NOT TURBID – THE CORMORANT’S POINT OF VIEW

(Oral Presentation # 28)

Strod T.* ¹, Izhaki I.², Katzir G.², Arad Z.¹
¹Department of Biology, Technion-Israeli Institute of Technology, Haifa 32000, Israel, zarad@techunix.technion.ac.il,
²Department of Biology, University of Haifa at Oranim, Qiryat Tivon 36006, Israel

Great Cormorants (Phalacrocorax carbo sinensis) forage underwater for fish by pursuit diving and are considered as a major pest to fisheries. Of the 20,000 over-wintering Great Cormorants in Israel, 9,000 roost in the Hula Reservation (northern Israel). Of them, ~90 % forage at the Sea of Galilee (25 - 40 km away) while only a few hundred forage in the murky fishponds nearby. We hypothesized that water turbidity must affect this foraging site choice and therefore assessed the effect of water turbidity on prey detection capacities of Great Cormorants. Five Cormorants were hand-reared in an aviary with a water tank, and fed on dead and live Carps (Cyprinus carpio) and St. Peter's fish (Tylapia spp.). The birds were trained to dive in an Y-shaped mesh tunnel, with a fish (9 cm long) presented in a box with a transparent door at either end. A significant prey side choice indicated the ability to detect the prey. The maximal turbidity that enables significant detection was determined at various prey distances. The Cormorants were able to detect the fish from at least 3.6 m in clear water (~0.2 ntu). An increase in turbidity to 1.0 ntu, reduced the maximal distance of detection to 2.5 m. When turbidity exceeded 3.5 ntu, the Cormorants were not able to detect the fish even from a distance of 1 m. The turbidity in the Sea of Galilee is 1.7 - 4.5 ntu and in the fishponds it is 15 - 300 ntu. These results suggest that turbidity is critically affecting the Cormorant’s prey detection capacity and that water turbidity is of a major importance in their foraging site choice (* Supported by the Israeli Ministry of Science).

CORMORANTS AND FISHERIES – STRONG BELIEFS AND WEAK FACTS IN A
CONFLICT OVER AQUATIC RESOURCES

(Oral Presentation # 14)

SUTER WERNER
Wildlife Ecology, Swiss Federal Institute of Forest, Snow and Landscape Research, Postfach,
CH-8903 Birmensdorf, Switzerland, Werner.suter@wsl.ch

Following the recovery of Great Cormorant (Phalacrocorax carbo) populations in Europe and Double-crested Cormorant (Ph. auritus) populations in North America, conflicts between fish-eating birds and freshwater fisheries have intensified. If both fish and bird populations are to be managed properly, scientifically rigorous studies quantifying the impact of birds on fish population dynamics as well as on fisheries are needed. Insight into bird-fish interactions is also of eminent scientific interest for understanding predator-prey relationships in general. This paper explores minimum standards for the kind of data needed in reliable impact assessments, measures existing papers against these standards, and reviews the current knowledge of the nature and strength of impacts. Possible impacts by birds depend on the type of fishery. In aquaculture, assessing fish removal by birds and calculating financial losses can be relatively straightforward, although in practice, the situation may be more complicated than generally thought. Fish farms have potential for conducting experiments to solve questions about foraging decisions in predators, but this potential has so far been neglected. Interference of piscivorous birds with aquaculture is, however, a problem restricted to certain areas, and the conflict as a whole is fuelled more by perceived problems of bird predation on free-living fish populations in more or less natural habitats. Here, empirical studies are usually the only way out, but modelling and simulations could greatly assist. Because basic data are often unavailable, using surrogate data sets (such as catch statistics) and indirect hypothesis testing may be necessary but should be cautiously applied. In reality, there are surprisingly few studies available worldwide that include enough data for assessing the impact of bird predation, and modelling attempts are almost nonexistent. In Central Europe, e.g., there is a large number of papers in semi-scientific journals apparently demonstrating deleterious bird impacts on fisheries, but none of these papers meets minimum standards of scientific rigour, and many even lack the most basic data. Nevertheless, these publications create the body of ‚evidence’ on which management decisions are based upon.

STOMACH CONTENTS ANALYSES OF GREAT CORMORANTS COMING FROM DIFFERENT AREAS OF AUSTRIA AND LICHTENSTEIN

(Poster Board # 24)

TRAUTTMANSDORFF JOSEF
Otto Koenig Institut, A-2000 Stockerau, Austria, okido@aon.at

The 133 stomachs examined came from three provinces in Austria (Niederösterreich, Steiermark, Vorarlberg) and from Lichtenstein where Cormorants have been shot on smaller rivers and ponds north and south of the Alps and on lake Bodensee. These stomach contents samples were accompanied by information about foraging grounds, time of shooting, hunting strategies of the birds, age, sex etc. There were big differences between stomach contents depending whether the birds were shot on lakes, ponds or rivers. This concerns both the general fitness of the birds and the kind of food taken. The stomachs of birds shot on smaller rivers contained Salmonidae and Thymallidae, those from shot ponds contained Cyprinidae, and those from lake Bodensee most frequently contained Percidae, Cyprinidae and Gasterosteidae. Nearly all Cormorants had taken food from the sites where they were shot enabling conclusions about the fish fauna of the rivers, ponds and lakes to be drawn.

How Zebra Mussels Dreissena polymorpha and Smelt Osmerus eperlanus
may affect Cormorants: water system studies at Lake IJsselmeeer,
the Netherlands

(Oral Presentation # 20)

VAN EERDEN MENNOBART R., VAN RIJN STEF, NOORDHUIS RUURD
Institute of Inland Water Management and Waste Water Treatment RIZA, P.O. Box 17,
8200 AA Lelystad, The Netherlands, m.veerden@riza.rws.minvenw.nl

Cormorants are part of the water system. Avian predation should be considered in relation to fish production and fish availability on one hand and the trophic state and food web structure on the other. The IJsselmeer/Markermeer system is a eutrophic down stream part of the river Rhine and part of the originally open system has been cut off from the river by a dam. Cormorants breed around the lake system, in recent years with four colonies (10,325 p. in 2000). Two organisms play a keystone role in this system, the bivalve Zebra Mussel (macrofauna) and the Salmonid Smelt (fish). These two abundant players in the foodweb control the biological functioning (food provision for waterbirds and fish) and are in turn influenced by water quality (nutrients). Recent changes in water quality of the river Rhine, compartmentalisation of the lakes and intensive fisheries have had a distinct effect on the state of the system. Zebra Mussels have a strong filtering capacity which influences underwater light climate; they also provide food for Roach Rutilus rutilus in turn an important prey for Cormorants. Planktivorous Smelt are eaten by Cormorants but its main effect is on zooplankton abundance in the lake, again responsible for bio-turbidity. A poor stock of mussels and a rich stock of smelt will thus deteriorate underwater hunting conditions. We argue the presence of cascade effects in the lake caused by shifts in trophic state. The effects of this process are illustrated by recent developments in the Cormorant population of the lake. It is concluded that single factor analysis of system ecology is not able to explain/forecast the expected direction of carrying capacity related problems. The challenge (and direction of our studies) is to continue gathering of relevant data and meanwhile to develop models to explain the described patterns.

Body condition of young Cormorants Phalacrocorax carbo sinensis in relation to cohort dependent survival

(Oral Presentation # 07)

VAN RIJN STEF, ZIJLSTRA MENNO, VAN EERDEN MENNOBART R.
Institute of Inland Water Management and Waste Water Treatment RIZA, P.O. Box 17,
8200 AA Lelystad, The Netherlands, s.vrijn@riza.rws.minvenw.nl

Body condition of nestling Cormorants in the old colony of Oostvaardersplassen (Lake IJsselmeer, the Netherlands) is compared with that of Vlieland, a recent settlement (Wadden Sea). Vlieland birds were heavier, irrespective of year and corrected for age, pointing at differences in food provisioning between the two colonies. Long term registration of body condition of young at the time of ringing in Oostvaardersplassen shows strong fluctuations. Relative body condition is related to minimum life span as estimated by the resighting of colour ringed birds. The contribution of body condition to the estimated number of fledglings as measured colony wide is discussed. It is concluded that biometric studies are necessary if one is to model colony development in detail.

The influence of Great Cormorant Phalacrocorax carbo sinensis predation on the fish stocks of lake Beulakerwiede, The Netherlands

(Oral Presentation # 09)

VeldkampRonnie*¹, Klinge Marcel^2

1 Bureau Veldkamp, De Rikking 46, NL-8332 CG Steenwijk, The Netherlands, veldkamp16@zonnet.nl, ² Witteveen + Bos, Van Twickelostraat 2, PO Box 233, NL-7400 AE Deventer, The Netherlands

The Cormorant colony of Wanneperveen, the oldest of The Netherlands, grew from 375 breeding pairs in 1983 up to 1,050 pairs in 1993. While the number of birds grew, Lake Beulakerwiede, a shallow eutrophic lake situated in the vicinity of the colony, became an important feeding area, where often mass feeding of more than 1,000 ex. occurs. Data on the diet of the Cormorants in 1992 point out that the birds consume relatively large quantities of 15 - 25 cm fish. Cormorant predation on Lake Beulakerwiede has had, and probably still has, a strong influence on the length composition of the fish stock. Coinciding with the increased Cormorant predation, a strong decline of the biomass of 15 - 25 cm fish and a strong increase of the biomass of fish <15 cm was observed. This shift in length distribution was probably caused by overexploitation of the 15 - 25 cm fish. It created favourable conditions for small piscivorous birds like Great Crested Grebe, Common Tern, and Black Tern. Because the total withdrawal by Cormorants probably did not exceed the total production capacity of the fish stock, the total fish biomass did not decrease.

CORMORANTS: A NEW INTERNET SITE TO PROMOTE RESEARCH AND
KNOWLEDGE ON THE PHALACROCORACIDAE

(Poster Board # 01)

VOLPONI STEFANO
Department of Biology, University of Ferrara, Via Borsari 46, I-441000 Ferrara, Italy, svolponi@racine.ra.it

In the last few years, the Internet has undergone dramatic development. Thanks to its world-wide accessibility, improved quality, speed of downloading, and easier and cheaper connection, the Internet creates new opportunities for communication and knowledge sharing. Therefore, the Internet provides an ideal way to quickly inform and keep in touch with the diverse and cosmopolitan community of people interested in Cormorants and related topics. With this in mind, I have begun work on a site dedicated to Cormorants with the following goals: (1) to establish a place for the Wetland International Cormorant Research Study Group to enlarge its audience and promote its activities, and to encourage collaboration and quick interactions among members; (2) to make available a virtually unlimited and easy to update database for all kinds of resources related to Cormorants (documents, data, literature, pictures, meeting announcements, etc.); (3) to be a point of reference for professional ornithologists as well as for birdwatchers, students and teachers, fish-managers and any others interested in aspects of Cormorant biology and ecology. The Cormorant site is open to contributions from individuals who want to share their experience, scientific records and ideas, and as such is the "Cormorant community’s" site. At the moment the site’s contents are limited, but the site is intended to be "permanently under construction", so much additional information will be incorporated, depending on further needs, requests, suggestions and feedback. The Cormorant site address is: http://web.tiscalinet.it/sv2001.

Double-crested Cormorant Research, Conservation, and Management

(Oral Presentation # 30)

Werner Scott J. ¹, Hanisch Shauna L. ^2

1United States Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, Mississippi Research Station, P.O. Drawer 6099, Mississippi State University, Mississippi 39762, USA, swerner@netdoor.com,
²United States Department of Interior, United States Fish and Wildlife Service, Division of Migratory Bird Management, Arlington, Virginia 22201, USA, shauna.hanisch@fws.gov

The Double-crested Cormorant (Phalacrocorax auritus), the most abundant of North America’s four Cormorant species, has rebounded to high numbers after near extirpation in the 1960s and early 1970s. Enhanced environmental regulations and increased food availability facilitated the resurgence of Double-crested Cormorant populations by the mid-1970s and numbers have continued to increase steadily in most geographic regions through the 1980s and up to the present. The North American population of DCCOs has been estimated at 1-2 million birds. Concerns about impacts of DCCOs on aquacultural stock, sport fish populations, other birds, vegetation, private property, and local economies have been raised. Economic impacts to commercial Catfish aquaculture are the best documented of these impacts. Due to the species’ dramatic population increase and the biological and socio-political importance of these various concerns, the U.S. Fish and Wildlife Service, in cooperation with USDA/APHIS/Wildlife Services, is currently preparing an Environmental Impact Statement and national management plan to consider the environmental impacts and effectiveness of various management alternatives for reducing human-Cormorant conflicts.

POTENTIAL IMPACT OF DOUBLE-CRESTED CORMORANTS (Phalacrocorax auritus) ON OTHER COLONIAL WATERBIRDS

(Poster Board # 31)

WESELOH CHIP D.V., HAVELKA TANIA
Canadian Wildlife Service, 4905 Dufferin St., Downsview, Ontario Canada M3H 5T4, chip.weseloh@ec.gc.ca

In 2000, we initiated a study of possible impacts of Double-crested Cormorants, Phalacrocorax. auritus, on Black-crowned Night-Herons, N. nycticorax, on the Canadian Great Lakes. We examined 25 sites which had been censused for Cormorants and Night-Herons in 1991 and 1999/2000. At eight sites (32 %), Night-Heron numbers declined; Cormorant numbers had increased at 7 of these 8 sites (88 %). At 17 sites (68 %), Night-Heron numbers increased. However, 76 % (13) of these sites were new nesting areas for Night-Herons. Of Night-Heron sites visited in 2000, 29 % had been abandoned in light of increasing Cormorant numbers or were in imminent danger of being overrun by Cormorants. In light of Cormorant numbers, Night-Herons may be leaving historical nesting areas and establishing new colonies.

TRANSCONTINENTAL CONNECTIONS: CORMORANT-FISHERIES CONFLICTS, PERCEPTIONS AND REALITIES ON BOTH SIDES OF THE ATLANTIC

(Poster Board # 33)

WIRES LINDA R.¹, CARSS DAVID N. ², CUTHBERTFRANCESCA J. ¹
¹ University of Minnesota, Department of Fisheries & Wildlife, 200 Hodson Hall, 1980 Folwell Avenue, St Paul, MN 55108-6124, USA, wires001@maroon.tc.umn.edu,
² Centre for Ecology & Hydrology Banchory, Hill of Brathens, Banchory, Aberdeenshire, Scotland, AB31 4BW, d.carss@ceh.ac.uk

We report on a recent Workshop for scientific discourse on Double-crested Cormorants and fisheries conflicts held in Plymouth, Massachusetts in November 2000. There has been much public and scientific debate in North America about Double-crested Cormorant (DCCO)-fishery conflicts and attempts to resolve them. This workshop provided an opportunity for wildlife managers, ornithologists and fisheries biologists from across the N. American continent to discuss important differences in perspectives and approaches to this complex problem in a productive and dispassionate manner. Very similar conflicts exist between fisheries interests and a rapidly expanding population of Great Cormorants in Europe and there are strong parallels in terms of both scientific and political attempts at conflict resolution. Thus a European representative of The Wetlands International Cormorant Research Group also contributed to the workshop offering a first-hand opportunity to exchange ideas and information on Cormorant-fishery interactions across N. America and Europe.

Historic and Current Distribution of the Double-crested Cormorant (Phalacrocorax auritus) in Eastern and Central North America: Perceptions of Population Recovery

(Poster Board # 34)

Wires Linda R. ¹, Cuthbert Francesca J. ¹, Trexel Dale R. ¹
Department of Fisheries and Wildlife Conservation, University of Minnesota, St. Paul, MN 55108, USA, wires001@maroon.tc.umn.edu

In North America, the Double-crested Cormorant (Phalacrocorax auritus) is widely distributed across five broad geographic regions: Canadian and U.S. interior, Northeast Atlantic Coast, Southern U.S., Alaska, and Pacific Coast. We review historic and current breeding and wintering records to determine historic distribution (pre-1900), current distribution (1970-1999), and the extent of range expansion in eastern and central North America. Current distribution data came from university, state and provincial biologists, and our own field surveys. Historic data were obtained from early naturalist and ornithological accounts. Records suggest that Double-crested Cormorants may have been present in large numbers throughout much of their current range, but their numbers sharply declined through the late 1800s, causing the species to disappear from some areas. The population gradually increased through at least the mid-1900s, and then numbers again sharply declined in the 1960s-1970s. In the late 1970s, the population once again began to recover. In some areas where Double-crested Cormorants are believed to have recently (post 1900s) established themselves as breeders, historic records indicate that the species is re-colonizing rather than pioneering. The historic range of this species is important for how the recent species recovery/expansion is being perceived by the public and resource managers. For instance, in some areas where the Cormorant is resuming its historic status as a breeder or year round resident, the species is being viewed as an invader rather than as an integral part of the ecosystem, which may have significant implications for how the species is managed.

Diet composition of GREAT Cormorants (Phalacrocorax carbo Sinensis)
in the Drawien National Park

(Poster Board # 25)

Wziatek Bogdan ¹, Martyniak Andrzej ¹, Szymanska Urszula ², Kozlowski Jacek ¹, Dostatni Dariusz ¹
¹ Department of Fish Biology and Culture, University of Warmia - Mazury, Oczapowskiego 5,
10-957 Olsztyn, Poland, kbhr@uwm.edu.pl, ² Department of Environment Protection,
University of Warmia - Mazury, Olsztyn, Poland

Protection of Great Cormorants may be in conflict with protection of populations of fish species, some of which are in danger, especially if subject to high predation rates. The Drawien National Park is a place where many threatened species exist, including fishes such as: Trout (Salmo trutta m. lacustris), Vendace (Coregonus albula), Vimba (Vimba vimba) and other species. To determine whether Cormorants consume these species, we examined Cormorant diet composition in the Drawien National Park, situated in northwest Poland, and comprised by 16 lakes and 2 rivers. The breeding colony (60 pairs) is situated on Lech Island on Ostrowieckie Lake. Pellets were collected from the colony from March to September 1997. Results of the study were based on 705 prey items, and included 14 fish species and one species of crayfish (Orconectes limosus Raf.). Roach (45.1 %) and Perch (37.6 %) dominated the diet. Percentage frequency of other species was less than 7 %. The presence of Vendace was noted in September (2.1 %) and Vimba in July (0.4 %). The body length of fish consumed was about 15 cm for Roach and Perch; 30 cm for Pike; and 50 cm for Eel. Presently Cormorants do not appear to have significant impacts on threatened fish species. However, with growing Cormorant numbers, the situation may change. Therefore interactions between Cormorants and threatened fish species in this area require continued monitoring and study.

TAMING THE DELTA OF THE SENEGAL RIVER, WEST AFRICA: EFFECTS ON CORMORANT AND DARTER POPULATIONS

(Poster Board # 35)

YÉSOU PIERRE*, TRIPLET PATRICK
Direction des Études et de la Recherche, Office National de la Chasse et de la Faune Sauvage, 53 rue Russeil, 44000 Nantes, France, p.yesou@onc.gouv.fr, and Patrick Triplet, Réserve naturelle de la baie de Somme, Station Biologique de Blanquetaque, 1 place de l'Amiral Courbet, 80100 Abbeville, France

The delta of the Senegal river (c. 320,000 ha) has been gradually dammed, mostly over the 1970-80s, and its habitats have been dramatically modified. The loss of natural deltaic conditions and the artificial flooding of wetlands led to major changes in water quality, aquatic vegetation, and fish stocks. Meanwhile, numbers of both Long-tailed Cormorant Phalacrocorax africanus and Darter Anhinga melanogaster rufa have decreased markedly (respectively, 1,200 pairs in 1981 and 600+ pairs in the 1960s, but < 1,000 individuals and 80-250 individuals by the end of the breeding season in the 1990s). Conversely, the Great Cormorant P. carbo lucidus population increased from under 200 pairs in the 1960s to at least 1,250 pairs in the mid-1990s. Reasons for such changes will be discussed.