Yano and Dahlheim: Depredation of bottomfish on longline catches by Orcinus orca 



359 



Table 1 



Areas and stations where killer whales, Orcinus orca, were encountered (X) during Japan-U.S. cooperative longline surveys 

 (1980 to 1989). B-II and B-III areas were not surveyed (— ) in 1980 and 1981. Asterisks (*) indicate the stations where killer 

 whales were encountered but no depredation occurred. 



Area' 



EA 



EA 



EA 



EA 



EA 



B-l 



B-l 



B-l 



B-l 



B-l 



B-II 



B-II 



B-II 



B-II 



B-II 



B-II 



B-II 



B-II 



B-II 



B-III 



B-III 



B-III 



B-III 



SH 



KO 



Total per 



St. no. 



35 

 36 

 37 

 38 

 59 

 30 

 31 

 32 

 33 

 34 

 17 

 18 

 19 

 20 

 22 

 25 

 26 

 27 

 28 

 7 



10 

 12 

 13 

 65 

 83 



year 



Year 



1980 



1981 



1982 



1983 



1984 



1985 



1986 



1987 



X 

 X 

 X 



X 

 X 



X 

 X 



1 



X 

 X 

 X 



X 

 X 



X 

 X 



X 



X 

 X 

 X 

 X 



X 

 X 

 X 



8 



X 

 X 

 X 



X 

 X 

 X 

 X 



1988 2 1989 



X 

 X 



X 



X 



X* 



X 



X 



X 



X 



X 



X* 



X 



X* 



15 



X 

 X 



X 

 X 



Total 

 per 



station 



1 

 1 

 3 

 1 

 1 

 2 

 6 

 4 

 7 

 2 

 2 

 1 

 1 

 3 

 3 

 6 

 5 

 3 

 1 

 1 

 1 

 2 

 1 

 1 

 1 



60 



EA = Eastern Aleutian Islands; B = Bering Sea; SH = Shumagin Islands; KO = Kodiak Island, see Figure 1 for areas. 

 Detailed observations of killer whale predation were documented. 



catch rates for years with and without killer whale pre- 

 dation ranged from 9.2 to 92.4% for sablefish, from 2.2 

 to 90.4% for Greenland turbot, and from 1.4 to 80.3% 

 for arrowtooth flounder (Table 4). 



Between-year comparisons (REY) for catches of all 

 species at the same station (except for 1982 of sable- 

 fish) indicate catches were lower in years with killer 

 whale depredation (Table 5). The average catch rates 

 of sablefish and Greenland turbot for stations with 

 killer whale depredation were significantly lower 

 than in stations without depredation (ANOVA, 

 P<0.05). However, the average catch rate of 

 arrowtooth flounder (for stations with killer whale 

 depredation) was not significantly lower than that 

 for stations without killer whale depredation 

 (ANOVA, P>0.05). Depredation rates (REY) calcu- 

 lated from the average catch rates for stations with 

 and without killer whale predation ranged from 33.4 

 to 84.1% for sablefish, from 53.3 to 82.6% for 



Greenland turbot, and from 17.0 to 70.8% for 

 arrowtooth flounder (Table 5). REY values calculated 

 from average catch rates for years with and without 

 killer whale depredation were slightly lower than 

 REA values (Table 6). 



Predation rates based on the average catch landed 

 (REA and REY values) were higher than those rates 

 ( RNT and RNS values) calculated directly from count- 

 ing heads, lips, and gills of fish remains on the deck 

 during the 1988 survey (Table 6). Depredation rate, 

 based on the four different methods of calculations (i.e. 

 RNT, RNS, REY, and REA), suggested that whales took 

 14-60% of the sablefish, 39-69% of the Greenland tur- 

 bot, and 6-42% of the arrowtooth flounder. 



Size of fish consumed by killer whales 



The size of the fish taken by whales was determined 

 by measurements of HL or ML. The relationships 



