In 1965, Denmark began an offshore gill-net fishery for Atlantic salmon in the Davis Strait off the coast of west Greenland. The offshore fishery catch increased from 36 metric tons in 1965 to more than 1,200 metric tons in 1969, and then gradually decreased.
The fact that large numbers of seabirds—almost entirely thick-billed murres (Uria lomvia)—were being drowned in the salmon gill nets was brought to the attention of the International Council for Bird Preservation at its 15th World Conference in 1970. The Council's recommendation was submitted to the Danish government and stated: "... having noted that during the 1969 fishing season about 250,000 individuals of Brunnich's guillemot or thick-billed murre (Uria lomvia), a pelagic diving bird, were caught in these drift nets and drowned, which number represents no less than 25 percent of the Greenland population and exceeds its annual reproductive capacity; urges the Danish Government, and the national governments of all other countries involved in this fishing, to take all possible measures to eliminate this very serious problem."
The figures in the recommendation were not supported by research; they appeared instead to have been derived from the observed mortality on an offshore fishery vessel in 1965, which was then related to the salmon catch on that vessel and applied to the total catch of the inshore fishery in 1964 (Anonymous 1969). Studies in 1969 and 1970 by the Fisheries Research Board of Canada finally gave a firm basis for the earlier, though poorly substantiated concern. On the basis of the assumption that the ratio of salmon to murres caught in experimental fishing applied to the commercial fishery, an estimate of an annual mortality of 0.5 million murres (±50%) was made on the basis of a salmon catch of 1,200 metric tons (Tull et al. 1972).
The birds being killed were from colonies in west Greenland, the eastern Canadian Arctic, and possibly east Greenland and Spitzbergen. Coupled with other known causes of mortality (particularly hunting on the Greenland and Newfoundland coasts, an unknown but definitely substantial kill from oil pollution, a calculated mortality of pre-fledging young, and an unknown natural post-fledging mortality) there is no doubt that the estimated annual production of 1.5 million chicks from west Greenland and the Canadian Arctic was less than the estimated total annual mortality (Tull et al. 1972). Thus, it comes as no surprise that recent surveys of murre populations of west Greenland and the Canadian Arctic have revealed massive declines in numbers (Evans and Waterston 1976; D. N. Nettleship, personal communication). It is therefore encouraging news that, as a result of an agreement between the United States and Denmark, the offshore salmon gill-net fishery was terminated at the end of the 1975 season. The inshore fishery remained in operation, however, but was restricted to a total annual salmon catch of 1,100 metric tons.
Pacific Offshore Salmon Gill-net Fishery
In the north Pacific Ocean, the Japanese gill-net fisheries for salmon (Oncorhynchus spp.), which have operated since 1952, might be expected to have an even more destructive effect on seabirds, since the annual salmon catch by the three Japanese salmon drift-net fisheries was about one hundred times that in west Greenland in recent years. The first, the mothership fishery, comprising about 369 catcher-boats[53] serviced by 11 mother-ships, operates west of 175°W and generally north of 46°N during the summer. The second, the land-based fishery of about 325 ocean-going vessels, operates west of 175°W and south of 46°N; and the third, the coastal fishery, made up of about 1,380 short-haul vessels, operates off Hokkaido. The relative salmon catches of these three fisheries is on the order of 1:1.34:0.65.
Data collected on U.S. National Marine Fisheries Service research vessels in 1974 (obtained through the cooperation of Francis M. Fukuhara and Richard Bakkala, Northwest Fisheries Center, Seattle, Washington) give, for the first time, an estimate of the magnitude of the incidental seabird kill of the Japanese salmon gill-net fishery. The kill data are available only from the mothership area and from an area east of it to 165°W. The Japanese salmon fishery is restricted to waters west of 175°W by agreement with the United States. Bird kills from the other two areas may be estimated by the relative salmon catch figures for the areas, assuming that seabird densities, species composition, and catch effort are similar.
An estimate of the total kill of seabirds in the mothership area may be made by calculating the bird mortality per length of gill-net set by research vessels, multiplied by the total length of gill nets set by the 369 catcher-boats of the Japanese mothership fishery. About 4,666 km of nets are set and retrieved daily during the approximately 65-day fishing season. The estimated annual mortality in the mothership area is about 75,000 to 250,000 birds. The lower number is based on data from 10 cruises (450 km of nets set) west of 175°W, within the area of the mothership fishery. The higher number is based on data from 20 cruises, including those in the first figure, west of 165°W, and covering the period 18 April to 3 September 1974 (956 km of nets set), whereas the mothership fishery usually operates between mid-May and late July. Assuming similar seabird densities and catch per unit of effort in the areas of the land-based and coastal fisheries, the estimated annual mortality is between 214,500 and 715,000 birds. Since 1952, as many as 4.7 million birds may have been killed by the Japanese salmon gill-net fishery. It must be stressed that seabird densities and catch per unit of effort are not known to be similar for the areas in question; consequently the projection of bird kill figures from one area to all three is speculative.
In the mothership area and adjacent seas to the east, in addition to murres (48% of birds killed), significant numbers of shearwaters, Puffinus spp. (27%); puffins (9%); and fulmars, Fulmarus glacialis (5%) are killed, as are lesser numbers of small alcids, albatrosses (Diomedea spp.), and storm-petrels. The murres and puffins taken in the mothership area are of U.S. and U.S.S.R. origin, and the shearwaters come from New Zealand, Australia, and Chile. In the coastal fishery area, Japanese and U.S.S.R. alcids are taken. Available knowledge of the populations of the species making up the bulk of the kill, which has been taking place for 20 years, is insufficient to suggest whether their annual reproduction can tolerate such losses. Prohibition of fishing within 160 km of North Pacific seabird breeding islands would help to decrease losses of alcids of U.S. origin, but would not help the shearwaters from the southern hemisphere.