quent intervals (Sanger 1976; Fredin et al.^). A 

 similar fishery in the North Atlantic between 1965 

 and 1976 was responsible for the deaths of large 

 numbers of the thick-billed murre, Uria lomvia, 

 and significant reductions in its breeding popula- 

 tions (Tull et al. 1972). Recent work in the North 

 Pacific and Bering Sea by Sano ( 1978) and King et 

 al. (1979) indicated that large numbers of seabirds 

 are killed annually in the Japanese salmon 

 fishery also. 



Previous estimates of seabird mortality result- 

 ing from the Japanese high-seas and land-based 

 gill net fisheries were based on data gathered from 

 research nets only (e.g., Sano 1978; King et al. 

 1979). These nets include both smaller and larger 

 mesh sizes than nets used in the commercial 



^Fredin, R. A., R. L. Major, R. G. Bakkala, and G. K. 

 Tanonaka. 1977. Pacific salmon and the high seas salmon 

 fisheries of Japan. Processed Rep., 324 p. Northwest 

 and Alaska Fisheries Center, NMFS, NOAA, 2725 Montlake 

 Boulevard E., Seattle, WA 98112. 



fishery We wished to investigate if mesh size influ- 

 enced bird mortality rates, and if so. to reassess 

 the impact of gill net fisheries on seabird mortal- 

 ity. Since previous estimates of the total bird catch 

 were based on data averaged over broad regions, 

 we also investigated the geographic variation in 

 catch rates to determine whether in .some areas 

 they could potentially be having an important im- 

 pact on local bird populations. 



Method .s 



We participated in cruises aboard Japanese re- 

 search vessels during 1978 and 1979 as shown in 

 Figure 1. The Oshoro Maru and Hokusei Maru 

 deployed research nets and the Hoyo Maru No. 67 

 deployed a small series of research nets between 

 two extensive spans of commercial nets. Research 

 and commercial nets differ significantly only in 

 the variety of mesh sizes used. In this study the 

 mesh sizes in the research nets ranged 37 to 233 



O HOYO MARU NO. 67, 1st Cruise, June 



O " " " ,2nd Cruise, July. 



▲ OSHORO MARU, June-July. 



 NOJIMA MARU Catcher Boat, July. 



1978 

 ▲ OSHORO MARU, June-July. 



D HOKUSEI MARU, August. 



FIGURE 1.— Cruise tracks i linesi and net setting stations (symbols) where observations were made in 1978 and 1979. 



801 



