MORTALITY TO MARINE BIRDS THROUGH COMMERCIAL FISHING 



197 



The figures in the recommendation were not 

 supported by research; they appeared instead 

 to have been derived from the observed mor- 

 tality 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 defi- 

 nitely substantial kill from oil pollution, a cal- 

 culated mortality of prefledging young, and 

 an unknown natural postfledging 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, per- 

 sonal communication). It is therefore encour- 

 aging news that, as a result of an agreement 

 between the United States and Denmark, the 

 offshore salmon gill-net fishery was termi- 

 nated at the end of the 1975 season. The in- 

 shore 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 2 serviced by 11 motherships, 

 operates west of 175W and generally north 

 of 46 N during the summer. The second, the 

 land-based fishery of about 325 ocean-going 

 vessels, operates west of 175W 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 (ob- 

 tained through the cooperation of Francis M. 

 Fukuhara and Richard Bakkala, Northwest 

 Fisheries Center, Seattle, Washington) give, 

 for the first time, an estimate of the magni- 

 tude of the incidental seabird kill of the Japa- 

 nese salmon gill-net fishery. The kill data are 

 available only from the mothership area and 

 from an area east of it to 165W. The Japa- 

 nese salmon fishery is restricted to waters 

 west of 175W 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 sea- 

 bird densities, species composition, and catch 

 effort are similar. 



An estimate of the total kill of seabirds in 

 the mothership area may be made by calculat- 

 ing 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 sea- 

 son. The estimated annual mortality in the 

 mothership area is about 75,000 to 250,000 

 birds. The lowemumber 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 



2 This figure is based on data through 1971. Since 

 then, the number of catcher-boats has decreased 

 to 332 in 1974 (F. M. Fukuhara, personal com- 

 munication). 



