Mortality to Marine Birds Through Commercial Fishing

Warren B. King

International Council for Bird Preservation
Smithsonian Institution, Washington, D.C.

R. G. B. Brown

Canadian Wildlife Service
Dartmouth, Nova Scotia, Canada

and

Gerald A. Sanger [52]

U.S. National Marine Fisheries Service
Seattle, Washington

Abstract

Commercial fishing has been responsible for incidental mortality of seabirds for centuries, but with the advent of offshore salmon gill-net fishing in the North Pacific in 1952 and in the North Atlantic in 1965, the magnitude of this kill has increased, and there is strong indication that populations of some seabirds are being adversely affected. Murres (Uria spp.) are most frequently killed, although several other species are caught in lesser numbers. The seabird resources of several nations are involved in this mortality. Longline fishing and inshore gill-net fishing for salmon and cod also are responsible for mortality of seabirds, although usually not in significant numbers.

That the activities of commercial fishermen have caused mortality of marine birds surprises no one nowadays. Traditions of exploitation of marine birds by fishermen date from previous centuries, and fishing has contributed to the extinction of some species. For example, great auks (Pinguinus impennis) and other birds were used as food by fishermen fishing for Atlantic cod (Gadus morhua) on the Grand Banks of Newfoundland since the beginning of that fishery in the early 16th century (Collins 1884; Lucas 1890). The last great auk died in 1844, but smaller species, such as storm-petrels (Hydrobatidae), greater shearwaters (Puffinus gravis), and black-legged kittiwakes (Rissa tridactyla), were used for food until rather recently (Templeman 1945). This practice has now lapsed, however.

Inshore Fisheries

Until the advent of the offshore salmon gill-net fisheries in the North Pacific in 1952 and the North Atlantic in 1965, most seabird mortality in these areas was the result of local fishing close to shore. Several records of such bird mortality have been published. For example, 8,000-10,000 seabirds—presumably mostly alcids—were reported caught annually off Hammerfest in northern Norway (Holgersen 1961). E. Brun (personal communication) reported that the longline fishery off the coast of Norway is having serious consequences on Norwegian populations of murres.

Numbers of alcids are caught in nets set for Atlantic salmon (Salmo salar) around the coasts of Ireland and Scotland (Biddy 1971). A similar situation exists along the west Greenland coast, although it is overshadowed there by the direct exploitation of huge numbers of alcids by hunting. Nonetheless, in 1967 for example, 15,000 alcids were recovered from fish nets in southwestern Greenland, where they were sold as food (Evans and Waterston 1976). The annual salmon catch of the west Greenland inshore fishery has fluctuated between 60 and 1,500 metric tons and has averaged about 1,000 tons. There are no data comparing the relative catch of birds and fish in this fishery.

Atlantic cod follow the spawning capelin (Mallotus villosus) inshore along the east coast of Newfoundland in late June and early July. They are traditionally fished with traps and handlines along this coast, but there has been a recent trend toward using drift nets set on the bottom. Since alcids feed extensively on capelin at this time, many are caught in the cod nets set in areas close to the large colonies off Witless Bay (D. N. Nettleship, personal communication). Additionally, gill nets are set at the surface for salmon in the same area. Common murres (Uria aalge) are most affected, but Atlantic puffins (Fratercula arctica) are also taken.

There are as yet no estimates of the total alcid mortality from this fishery, although the annual catch of birds is believed to be smaller during the present than during the last decade because the fishing effort is reduced, and fishermen in the area now avoid setting nets near alcid concentrations because of the annoyance of having to remove the birds from their nets. The Witless Bay colonies contain over 77,000 pairs of common murres, or 11% of the total eastern North American population, and over 235,000 pairs of Atlantic puffins, or 71% of the North American population outside of Greenland (Brown et al. 1975). The potential danger is obvious.

There are few data on mortality of seabirds from inshore commercial fisheries in the North Pacific. Some mortality of alcids has been shown to take place in Cook Inlet, Alaska, from beach-netting for Pacific salmon (Oncorhynchus spp.) adjacent to seabird rookeries and from drift-netting in the inlet (D. A. Snarski, personal communication), but this mortality has not been quantified.

Bilateral agreements between the United States and Japan, the U.S.S.R. and the Republic of Korea, concerning the use of inshore waters adjacent to some of the Aleutian Islands, Kodiak, Nunivak, St. Matthew, St. George, Kayak, and Forrester Islands permit trawling, longlining, and loading fish and fuel in some of these areas and at certain periods. Although these activities may affect the seabirds of these areas, the extent of the effects are not known (U.S. Department of the Interior, Alaska Planning Group 1974). Murie (1959) indicated, however, that the disappearance of the ancient murrelet (Synthliboramphus antiquus) from Sanak Island, Gulf of Alaska, was probably due as much to fisheries as to the blue fox industry. It has been suggested that the Japanese murrelet (Synthliboramphus wumizusumi) may have declined as the result of fishing activities near breeding sites off the coast of Japan (Bourne 1971).

Atlantic Offshore Gill-net Fishery

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.

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.

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