WI - Cormorant Research Group The Group - Contacts published on 05 Marche 2001

(GDANSK 1993)

Drafted at the
3rd international meeting of the Cormorant Research Group
13-17 April 1993, Gdansk, Poland

Following on from meetings in Sweden (1985) and The Netherlands (1989), the third international meeting of the Cormorant Research Group was held in Poland and was attended by almost 100 participants from 20 countries: Austria, Byelorussia, Belgium, Bulgaria, Czech Republic, Denmark, Italy, France, Germany, Latvia, Lithuania, Norway, Poland, Portugal, Rumania, Sweden, Switzerland, The Netherlands, Ukraine and United Kingdom. A total of 70 papers was presented by leading experts on cormorants, particularly those studying the two sub-species in Europe, Phalacrocorax carbo sinensis and P. c. carbo.

The Group has always been award that the cormorant is an ecologically important species that is highly dependent on wetland habitats and is especially vulnerable when concentrated in breeding colonies. The Group believes that the countries which share cormorant populations should protect them, and the habitats that they use.

The Group notes that, at present, this is recognised in international legislation and agreements, such as the Ramsar Convention 1971, EC Birds Directive 79/409, Bonn and Berne Conventions 1983. Though both subspecies are afforded protection by these, P. c. sinensis id listed on Annex 1 of the EC Birds Directive 79/409 and thus qualities for special protection measures in the EC.

Many of the sites used by cormorants are also protected under such legislation and agreements, for example as Special Protection Areas or Ramsar sites, and some will obtain further protection under the Natura 2000" network of the EC Species and Habitats Directive.

The Group exists primarily to stimulate and coordinate research on all biological and ecological aspects of the species, to collect relevant data and to disseminate the results. The Group is conscious of the need to base management actions on sound scientific principles and findings.

The Group is aware of increasing conflict between fisheries and conservation organisations regarding cormorant damage, and notes that this was a principal reason for its formation in 1985.

Group members have chosen to study cormorants because they:

  1. are migratory birds that move between political boundaries and have long been vulnerable to different types and degrees of threat;
  2. are dependent on marine and freshwater wetlands, and are thus particularly exposed to habitat loss, changes in hunting pressure, pollution and other human activities affecting such habitats;
  3. represent top-predators in the ecological food-web and are therefore good indicators of the general health of the water environment;
  4. depend on fish and thus impinge on human interests, either commercial or social, giving the potential for real and perceived conflicts amongst fishermen, fishery managers and bird/nature conservationists.

The key findings of the Group to dale, as discussed at the Gdansk conference, can be summarised as follows, further details being available directly from the Group, or from its publications:


1. Cormorant populations have expanded greatly during the last 10-15 years from levels that were previously held low by man. There is still strong population growth in some areas, especially in the northern parts of the European range of P. c. sinensis, and the beginnings of (possible) sharp population increases are evident in central European areas also, such as Lithuania and Bulgaria.

2. In 1992, The European breeding populations were estimated at 105 000 pairs for P. c sinensis and 45 000 pairs for P. c. carbo. This is the first European wide estimate for P. c. sinensis, whose north-central European population alone rose from 40 000 pairs in 1988 to 77 000 pairs in 1992, a 93% increase. Census data for P. c. carbo from the same period are less complete, but the population increased by less than 20% during this time.

3. The most important breeding areas for both sub-species lie in north-western Europe. Denmark and The Netherlands together support more than 50% of breeding P. c. sinensis in Europe, whilst Norway and Great Britain arc the primary European breeding areas for P. c. carbo.

4. The number of cormorant breeding colonies varies greatly between countries.

In general, P. c. carbo uses a large number of colonies, which tend to be small in size. In contrast, P. c. sinensis uses fewer colonies, with some (usually 1-3) supporting a high proportion of a country's breeding population (often 50-66%). The adapt<ible P. c. sinensis has developed the habitat of ground-nesting in some areas (e.g. Denmark, Sweden, Poland).

5. There is recent evidence that the numbers of breeding pairs in some of the largest breeding colonies may be stabilising under natural (non-human) influences (e.g. Denmark, The Netherlands). However, there is strong evidence also to indicate that the populations of both subspecies arc still likely to increase. This is because new colonies are forming, and there is much apparently suitable habitat not yet occupied.

6. Under natural circumstances, young birds appear to be most important in the formation of new breeding colonies. There is evidence that movement between colonies by established breeders is relatively uncommon, and occurs mainly in response to human disturbance.

7. Winter numbers have increase in accordance with increases in the breeding populations, and 1992/93 estimates for the winter period indicate the presence of at least 150 000 P. c. sinensis and 120 000 P. c. carbo in Europe. However, these data are known to be incomplete and thus provide minimum estimates.

8. Currently, the most significant wintering areas in Europe for P. c. carbo are Norway, France and Great Britain. For P. c. sinensis - France, Italy and Spain, collectively supporting more than 50% of the population, are the primary wintering areas in western Europe.

9. Whilst new, potentially important, wintering areas are developing in central and eastern Europe, there is recent evidence that winter numbers in other parts of the range (e.g. Switzerland) may be stabilising.


10. Cormorant diet varies between locations and seasons. the most abundant of the prey types in the diet arc usually also amongst the most numerous species present. In some situations, cormorants may show a clear preference for one or more of the abundant prey type available to them, and thus may bc selective.

11. The total daily consumption of prey taken varies between locations and seasons, but is usually between 250-450 g. generally, the preferred size range of fish prey appears to be 10-20 cm.

12. The current composition of cormorant diet appears to have been strongly influenced by man, who has altered the natural balance of fish stocks in many situations (e.g. a reduction of predatory fish in the IJsselmeer, The Netherlands); increases in the biomass of roach in Switzerland; stocking with trout in Great Britain).

13. Cormorants appear adaptable with respect to their fishing strategies. For instance, social-fishing has developed in several countries.


14. Fishery interests in most European countries believe that cormorants cause damage to fish stocks and fisheries.

15. Impact by cormorants on fisheries may be of several, interrelated, types: economic (causing loss of income), ecological (effecting habitats, other species or ecotypes) or behavioural (affecting fish behaviour, and hence harvest rates, or the behaviour of fishermen themselves). This distinction has not always been made clear in reported cases of damage, and ecological and behavioural impacts have been little studied.

16. Relatively large losses of fish to cormorants at individual fisheries have

been demonstrated in a number of countries, mainly in extensive fish-farm areas and in the vicinity of fishing gear in lakes and coastal bays. However, the precise economic significance of such damage has rarely been quantified.

17. No significant impact by cormorants, leading to large reductions in entire fish populations, has been demonstrated under natural conditions (i.e. in natural habitats and at natural fish densities).

18. Cormorant impact is generally most significant in artificial situations, for example where fish are farmed at high density.

19. It is recognised that injury to individual fish may be important in some situations, perhaps reducing the survival and growth of fish, or reducing the economic value of the stock. However, such effects have yet to be demonstrated.


20. A comprehensive population model, incorporating 'bottle-necks' and mechanisms for population expansion, is currently not available for the cormorant. Thus, management actions are based on local knowledge only, and consequently the outcome of such measures is uncertain, especially in a European-wide context.

21. Shooting and other scaring techniques are already employed in many countries, though the success of these practices has rarely been documented. In many cases, this is believed to transfer the problem to other locations.

22. There are generally no precise guidelines or criteria applied to assess the scale of alleged damage to fish stocks and fisheries.

23. Whilst illegal persecution of cormorants occurs in many countries, the scale of this is usually unknown.

24. There is growing pressure in many European countries to control cormorants at the national level.

25.Only Denmark has an official, national. management plan for cormorants.

The Group wishes to make maximum use of existing valuable but dispersed information, and notes that the most effective and economic means of collating existing data and gathering critical new data is through the coordination of activities of both amateur and professional researchers throughout Europe.

The following were identified as the principal gaps in current knowledge relating to cormorants, and the Group hopes that these be recognised as priority research areas for the immediate future:

1. Fish population studies. Including research on fish population dynamics, particularly the role of cormorants compared to other factors.

2. Impact studies. Detailed studies at different fishery types, and in a range of situations.

3. Damage alleviation. Research into measures (including protective and management) that minimise impacts on fish stocks and fisheries where these occur.

4. Cormorant behaviour. Particularly research into how cormorants respond to regulation attempts, and the consequences of such actions with respect to numbers and distribution.

5. Habitat selection. Identification of the key factors influencing the selection of breeding, roosting and feeding sites.

6.Individual marking programmes. To allow further quantification of movements, mortality/survival, immigration and emigration. Especially needed in central and eastern parts of Europe (e.g. Poland, the Danube Delta).

7. Recruitment studies. Need to determine age of first breeding in many areas, and to study variations in recruitment rates.

8. Population regulation. Investigations of density-dependent regulation and carrying-capacity effects are needed.

9. Genetic analysis. To re-define the current range of the two sub-species in Europe, especially in areas where the birds are of unknown or mixed status (for example in some parts of Great Britain and France), and to study the genetic composition of 'isolated' groups, for example of cormorants in Sardinia.

The Group notes the need for a regular synthesis and up-dating of data on Cormorants at an international level.

The Group is keen to encourage continued participation from all countries currently involved in its activities, and would very much welcome more contact with people from the countries not represented to date. Also welcome would be more direct contact with fishery scientists and others who, so far, have had rather little involvement with the Group.

Key recommendations identified at the Gdansk meeting were as follow:

1. That governments and non-governmental organisations provide adequate resources to address the priority research needs identified above and, in particular, support relevant studies in areas where data are most lacking, for example, in central and eastern parts of Europe: Estonia, Latvia, Lithuania, Poland, Byelorussia, Ukraine, Czech and Slovak Republics, Hungary, Rumania, former Yugoslavia, Bulgaria and members of the Commonwealth States etc.

2. That consideration be given to the production of a European-wide management plan for cormorants. Given sufficient resources, the Group notes that its members could co-ordinate the production of such a strategy, and realises that full co-operation with fishery and bird conservation organisations will be essential. In the meantime, every effort must be made to ensure that certain general principles are common to all country-specific management plans.

3. That, to allow geographical and time-series monitoring, common standards of approach, methodology, data collection and handling be adopted by all those conducting research into cormorants.

4. That the type of damage (economic, ecological and behavioural) apparent at particular fisheries always be clearly distinguished and, where possible, scientifically quantified.

5. That actions against cormorants, both lethal and non-lethal, be appropriately designed and co-ordinated (regionally, nationally and internationally) with respect to the scale of the problem. The Group would welcome the opportunity to comment on proposed cormorant management before any actions are taken.

6. That this position statement be circulated to relevant governmental and non-governmental organisations.

The Group recognises that it will need to define clearly its principal aims and role over the next few years, and it may be desirable to enlist further expertise and expand its activities. The Group may soon affiliate with the Wetlands International (former International Waterfowl and Wetlands Research Bureau IWRB) thus providing a world-wide forum for those interested in cormorant species.

Drafted by J. S. Kirby
on behalf of the Cormorant Research Group.