Comparison of statistics of the salmon fisheries and associated bird kills from the North Atlantic and the North Pacific shows that the North Atlantic salmon fishery is concentrated in a relatively small area which is also along a major migration pathway of murres. Virtually all seabird mortality is confined to one species. Enough information is at hand to indicate that this cause of mortality, in conjunction with others known to be significant, is causing a drastic decline in the thick-billed murre population.
In the North Pacific, on the other hand, the fishery is more widely dispersed and the ratio of seabirds to salmon caught is much lower. Furthermore, several species are subject to mortality. No information is available to indicate whether alcid populations (which make up two-thirds of the kill) are stable or decreasing. The shearwaters, primarily sooty (Puffinus griseus) and slender-billed (P. tenuirostris), appear to be able to sustain not only these losses but also a sizable harvest of birds of the year (the so-called muttonbirds) on their New Zealand and Australian breeding grounds. Thus, although the latest estimates of the total standing stock of seabirds in the North Pacific in summer may be as high as 100 million (Sanger and King, this volume), and thus only about 1 of every 200 birds in the North Pacific region may be caught, the fact that a few species, particularly murres, are selectively caught raises questions about the impact of this fishery on populations of these species.
The U.S.-Japan Migratory Bird Convention of 1973 specifically protects all of the species thought to be subject to gill-net mortality in the Pacific. Thus, the Japanese salmon fleet apparently operates in constant violation of this convention.
Mortality of Albatrosses
A recent analysis of recoveries of Laysan albatrosses (Diomedea immutabilis) and black-footed albatrosses (D. nigripes) banded on the northwest Hawaiian chain from 1937 to 1969 showed that of a sample of 532 recovered birds, 57.4% of the Laysan species and 49.5% of the black-footed species were caught on fishhooks or in nets, and the means of recovery of many additional birds was thought to have been the same (Robbins and Rice 1974). It is likely that the large majority are taken on Japanese and U.S.S.R. longline tuna fishing gear. Although this cause of mortality is insignificant in terms of the total population of either species (only 0.2% of banded Laysan and 0.8% of banded black-footed albatrosses have been recovered by any means away from their breeding grounds), these species are protected by the U.S.-Japan Migratory Bird Convention. Furthermore, the possibility exists that individuals of the endangered short-tailed albatross (Diomedea albatrus) might be killed in this manner.
Long-term Effects of Developing Capelin Fishery in Northwest Atlantic
Capelin are important food fish for many seabirds in the northwest Atlantic, and the development and expansion of this fishery off eastern Canada must be carefully monitored. In theory, the capelin fishery ought not to seriously affect the birds because it is designed to exploit a surplus of capelin artificially created by the overfishing of Atlantic cod, the capelin's most important predator. It is hoped that there is no prospect of the overfishing that may have contributed to the recent drastic decline of the Peruvian anchovy (Engraulis ringens) and the seabird species dependent on it (Paulik 1971). However, the relative influence of overfishing and "El Niño" oceanographic conditions on the decline remains unclear. North Atlantic seabirds are, in any case, more versatile in their feeding habits (Belopol'skii 1961). But, the threat may be a subtle one. The important point to the seabirds may well be not merely the survival of a reasonably large capelin stock, but the presence of capelin schools in high densities in certain areas or at certain seasons. Lower densities might, for example, reduce the foraging efficiency of breeding birds, and hence their nesting success. The very large common murre colony on Funk Island, Newfoundland (500,000 pairs: Tuck 1960), might be particularly vulnerable. It lies close to an area where capelin are especially abundant and one which is already being exploited by the developing fishery.
References
Anonymous. 1969. Seabird slaughter. Sports Fish. Inst. Bull. 203:5.