オオミズナギドリの繁殖島と繁殖個体数規模,および海域,表層水温との関係

抄録

The global distribution and status of colonies of the Streaked Shearwater (Calonectris leucomelas) were elucidated on the basis of a comprehensive survey of all published literature, of unpublished literature, and a specimen survey and interviews. Information on colony population size was also obtained. The species occurs or occurred on a total of 98 islands in East and South-east Asia; consisting of 86 islands where breeding occurs (breeding islands), 11 islands with a high likelihood of breeding occurring, and one island with a low likelihood of breeding occurring. The 86 breeding islands, including three on which breeding has definitely or possibly ceased, are located in the following seas from 24-42°N, 121-142°E; 30 islands (35%) in the Pacific, 20 (23%) in the Sea of Japan, 16 (19%) in the East China Sea, 9 (10%) in the Yellow Sea, 7 (8%) in Tsushima Strait, and 4 (5%) around Taiwan. Japan hosts 72 (84%) of the 86 islands, South Korea hosts 6, China hosts 4, North Korea hosts 2, and Russia and Taiwan host one each. Thus most of the breeding islands are located on the continental shelf in the seas surrounding the Japanese Archipelago, an area of high marine productivity. Information on present colony status was unavailable for 21 (24%) of the 86 breeding islands, most of which were in Japan. Streaked Shearwaters still breed on the remaining 62 (72%) islands (52 of which are in Japan) but probably no longer breed on the three other islands. Most (80%) of the 86 breeding islands are situated in temperate areas within the 5-20°C zone of average Spring (March) surface water temperatures; 42% of the islands within the 15-20°C zone, 20% within the 10-15°C zone and 19% within the 5-10°C zone. The remaining 20% are within the 20-25°C (10%) and 1-5°C (9%) zones. Streaked Shearwater populations have recently tended to increase rapidly in the higher latitudes for this species (38-40°N) within the 5-10°C zone in the subarctic boundary between the warmer and colder currents in the northwest Pacific, where about 100, 000 birds breed on the uninhabited islands.
Breeding activities largely take place on those islands with a large Streaked Shearwaters population, which corresponds to about 30% of the breeding islands, while only 1-2% of the breeding population breed on the remaining 70% of islands hosting small or medium-size populations. The number of breeding birds on 36 islands (excluding Mikura Island, which has by far the largest population), was recently estimated as 816, 000 birds. As the Mikura Island total was roughly estimated to be 1, 750, 000-3, 500, 000 birds, the total number of Streaked Shearwaters breeding on the 37 islands amounted to 2, 566, 000-4, 316, 000 birds. Further population surveys of the Mikura Island population are needed, as this single estimate greatly influences the size of the estimated world population for this species. Up-to-date information on the status and distribution of Chinese and Korean populations of the Streaked Shearwater is also desired, as both countries have many offshore islands near the breeding zone for the species.