WI - Cormorant Research Group The Bulletin - No. 4, June 2000 Original papers

THE GREAT CORMORANT IN JAPAN

Michio Fukuda

Tokyo Sea Life Park, Rinkai­cho, Edogawa­ku, Tokyo 136­8587, Japan
mogufuku@beige.ocn.ne.jp

The Great Cormorant which inhabits Japan is classified Phalacrocorax carbo hanedae (Kuroda 1925). Formerly this subspecies was often considered a regional variation of P. c. sinensis which is widely distributed on the Eurasian continent, but most recent publications classify it as a subspecies (Johnsgard 1993, Orta 1992 etc.). This subspecies formerly inhabited the area from Sakhalin, Japan and Korea to Riu­Kiu Islands (Ornithological Society of Japan 1958). However, the condition of foreign distributions in unknown and cormorants do not inhabit Hokkaido and the Riu­Kiu Islands.

At present, the Japanese population is estimated to be about 40­50 thousand cormorants which are distributed in Honshu, Shikoku and Kyushu, and is gradually increasing. Although they still live sparsely, new regions are being used and the cormorant are steadily spreading due to dispersal caused by shooting for extermination and expelling in many places. Cormorants that moved to new regions were able to obtain fish which have been not utilized by other birds and have adapted to their new environment. On the other hand, food competition in established regions has been reduced and the breeding success was able to remain stable owing to a decrease in the population.

1. Changes in the distribution of the Great Cormorant in Japan

Great Cormorants have existed in many places of Japan for a long time. However, according to the detail distributional research, they were already living sparsely from about 112 years ago. McVean (1877), a surveyor who was invited by the Meiji Government, reported that the common cormorant ranks first amongst the birds of Yedo (Tokyo) as to numbers and permanent habitation".

Basically, cormorants feed on various kinds of fish that stay near the bottom of shallow salt water, brackish and fresh water areas. Cormorants decreased in many areas due to the expansion of human activities. The main reasons were; river and lake resources had begun to be efficiently utilized by people, and water pollution deteriorated with the use of chemical fertilizers, agricultural chemicals, effluent of factories, and domestic waste. With the decrease of fish, cormorant began to have a difficult time finding available food resources.

All inland colonies had disappeared by 1960. Because the population of these colonies was small (under 1,000 birds), cormorants were strongly influenced by these changes in their surroundings. Following this, the cormorants main foraging areas changed to include shallow coasts and river mouths located in big bays. These areas teemed with fish, and the cormorant began to mainly feed there. However, from 1960 to 1970 the lower reaches of the rivers were artificially repaired and the coasts were reclaimed for heavy industry, causing large size colonies to disappear or to be reduced.

Cormorants are a large sized bird and flock together in the same place, they excrete large quantities of white droppings on the soil and plants in their colonies and roosts. Long ago when fertilizers were not common, people scattered sand, or laid straw mats on the ground in cormorant colonies, and effectively gathered the excreta to utilize it as fertilizer. However, the disuse of excreta due to modernization, forest damage and foul smell caused the cormorants to be expelled from many regions.

Finally by 1971, less than 3,000 cormorants remained in 2 colonies. However, in the latter part of 1970, some colonies began to form in other regions, and now there are 30­40 various sized colonies. The main reasons for the increase in the Japanese population are; fish increase due to enforcement of environmental pollution regulations, improvement of water quality and the progress of water purification. Also, fish sources improved by the disappearance of large fish eating big birds such as cormorants for a long time. Furthermore, fish became abundant due to an increase in artificially stocked fish, large scaled fish farms, and an increase of fish that are able to live in unclean water.

2. Status of Cormorant

In many regions cormorants feed near river mouths and shallow coasts for half of the year (summer), and feed inland on lakes, ponds and at the middle and lower parts of rivers during the remaining half of the year (winter). In Japan cormorants begin to breed from autumn or winter, however breeding activities can be observed all year at some colonies. This very long breeding season was observed at the Shinobazu Pond colony that breed from the end of August to mid July of the following year. Therefore, the breeding activities of cormorants appears not to be influenced by the length of daylight (Fukuda 1997b). Other colonies have various breeding times and various breeding lengths.

There are 2 main habitats which are located around 2 big bays (Tokyo Bay and Ise­Mikawa Bay) that are separated by about 250 km. There were a few reports of movements between the 2 colonies for a long time. However, recent information on cormorants banded with color bands showed that some individuals moved between 2 habitats, and birds that moved over 100 km from their natal colony were increasing (Fukuda 1994). The main reasons for the increase of long distance movements are caused by the influence of exterminatory shooting and expelling due to various conflicts with people. The number of exterminated birds increased rapidly from the 1980s, and many regional exterminations are continued regularly every year. In 1998, over 5,000 cormorants (over 10% of Japanese population) were shot. The effects of this shooting has pressured the cormorants to move form their main habitats to form new wintering roosts in various regions.

3. Coexistence with cormorants in the future

Cormorants are gregarious and large quantities of fish are consumed near their habitats causing the botanical and biochemical soundings of their colonies and roosts to be gradually destroyed. Due to these reasons, in Japan where there are few areas untouched by man, many kinds of conflicts occur with the cormorant. Extermination of cormorants are carried out in many regions without scientific research on their destruction. After extermination of cormorants, stomach contents are seldom researched. The main reasons for extermination is the damages to stocked ayu (Plecoglossus altivelis) for sport fishing that the cormorant eat.

Most colonies will inhabit only unutilized islands or bird reserves. Although the present settled colonies situated in urban parks and reserves. However, management (exchange of soil, replanting of trees, etc.) of colonies is necessary for the cormorants to form a permanent residence. In some cases, control of breeding is necessary to alleviate fishing damages in the future. The Shinobazu Pond colony located in Ueno Park, Tokyo, is maintained by building artificial trees and exchanging the soil which covers the colony.

4. Research on the Cormorants in Japan

The status of cormorants in some areas was intermittently researched in the 1970s. Thereafter, ecological investigation began in some colonies. The breeding biology and behavior of cormorants was investigated by color­marked individuals. Breeding biology (first breeding age, relationship between age and breeding success, life­time success, mate relationship and natal colony tenacity, etc.) were investigated based on long term studies at the Shinobazu Pond colony (Fukuda 1992, 1997b etc.). The Japanese Cormorant Banding Group banded each colony with its own color band and the information from these color­banded birds that were observed, was collected from many places (Fukuda 1987). Juveniles tend to move a longer distance, and in some regions where colonies and roosts exist, many cormorants move within them.

The feeding habits of cormorants can only be researched by examining the stomach contents of exterminated birds and the regurgitated fish of chicks. Also, their feeding behavior was researched by the carbon isotope ratio of feathers (Mizutani et al 1990). Because there is little virgin forests in Japan, problems with forest damage always arise when cormorants utilized them. Affects on plants and soil in colonies due to excreta and breaking twigs for nest materials were researched (Ishida 1996a, 1996b, 1997a, 1997b).

Although the Cormorant distributed in Japan were classified as mentioned above P. c. hanedae, it is considered to be a close relative to the continental subspecies P. c. sinensis. The affinity of both was analyzed by DNA, and the differences between the western region (European habitats) and the eastern region (Chinese habitats) were compared. On the other hand, cormorants in the Kanto area are living in the most human crowed area of Japan where their breeding success has recently decreased. The progress of chemical contamination and accumulation of poisonous chemical materials in the cormorants' body are misgiven in this area. Indeed, higher accumulation levels of heavy metals (Saeki et al 2000), butyltin compounds (Guruge et al 1996a), organochlorines (Guruge et al 1996b), PCB (Guruge, Tanabe and Fukuda submit) and EDC were detected in cormorants. Cormorants can be used as an index of the degree of environmental pollution of our ecosystem.

I am very grateful to Ms. Susan Ishida who corrected my English manuscript.

References

Fukuda, M. 1987. Movements of Common Cormorants Phalacrocorax carbo marked with colored bands in Japan. Bull. JBBA 3:63­70 (In Japanese with English summary).

Fukuda M., 1992. Male­male pairing of the Great Cormorant (Phalacrocorax carbo hanedae). Colonial Waterbird Society Bulletin 16:62­63.

Fukuda, M. 1994. Long distance movements of color­banded Great Cormorants Phalacrocorax carbo from the natal colony. Bull. JBBA 9 :5­10 (In Japanese with English summary).

Fukuda, M. 1997a. Relationships between age and breeding success of Great Cormorant Phalacrocorax carbo hanedae at Shinobazu Pond colony, Tokyo, Japan. Suppl. Ric. Biol. Selvaggina 27:439­443.

Fukuda, M. 1997b. Relationships between an establish Great Cormorant colony and a small sub­colony. Bull. JBBA 12:31­38 (In Japanese with English summary).

Guruge K. S., S. Tanabe, M. Fukuda, S. Yamagishi and R. Tatsukawa, 1996a. Comparative tissue distribution of butyltin compounds in common cormorants (Phalacrocorax carbo) from Japan. Toxicological and Environmental Chemistry 58:197­208.

Guruge K. S., S. Tanabe, M. Fukuda, S. Yamagishi and R. Tatsukawa, 1996b. Accumulation pattern of persistent organochlorine residues in common cormorants (Phalacrocorax carbo) from Japan. Marine Pollution Bulletin 34:186­193.

Guruge K. S., S. Tanabe, and M. Fukuda, submit. Toxic assessment of PCBs by the 2,3,7,8­Tetrachlorodibenzo­p­dioxin equivalent in common cormorant (Phalacrocorax carbo) from Japan. Archives of Enviromental Contamination and Toxicology.

Johnsgard, P. A. 1993. Cormorants, Darters, and Pelicans of the world. Smithsonian Institution Press, Washington, D. C. and London.

Ishida, A. 1996a. Changes of soil properties in the colonies of the common cormorant, Phalacrocorax carbo. Journal of Forest Research 1: 31­35.

Ishida, A. 1996b. Effects of the common cormorant, Phalacrocorax carbo, on evergreen forests in two nest sites at Lake Biwa, Japan. Ecological Research 11: 193­200.

Ishida, A. 1997a. Effects of inhabitation of the common cormorant (Phalacrocorax carbo Kuroda) on forest ecosystem­a basic study for conservation and management of the habitat. Nagoya University Forest Science 16: 75­119 (In Japanese with English summary).

Ishida, A. 1997b. Seed germination and seedling survival in the colony of the common cormorant, Phalacrocorax carbo. Ecological Research 12: 249­256.

Kuroda, N. 1925. On a new Japanese Cormorant, with some notes and suggestions. Tori 4:336­350 (Japanese with English summary).

Mizutani, H. M. Fukuda, Y. Kabaya and E. Wada, 1990. Carbon isotope ratio of feathers reveals feeding behavior of cormorants. Auk 107:400­437.

Orta, J. 1992. Family PHALACROCORACIDAE (CORMORANTS). pp.326­353. in del Hoya, J., Elliott, A., and Sargatal, J. (eds.) Handbook of the birds of the world. Lynx Edicions, Barcelona.

Saeki, K., Y. Okabe, E.­Y. Kim, S. Tanabe, M. Fukuda and R. Tatsukawa, 2000. Mercury and cadmium in common cormorants (Phalacrocorax carbo). Environmental Pollution, 108:249­255.

Michio Fukuda, Tokyo Sea Life Park, Rinkai­cho, Edogawa­ku, Tokyo 136­8587, Japan
mogufuku@beige.ocn.ne.jp