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



367 



120 160 



Head length (mm) 



a 



c 

 ± 600 



40 60 80 100 120 



Maxillary length (mm) 



Figure 7 



Size of partially consumed arrowtooth flounder, Atheresthes 

 stomias. (A) The relationship between head length (HL) and fork 

 length (FL); (B) the relationship between maxillary length (ML) 

 and fork length (FL). 



killer whale pods are known to exist within the area 

 but only two pods have been involved in fishery in- 

 teractions. Although killer whales may frequently 

 travel between Prince William Sound and offshore 

 waters of the Gulf of Alaska, fishery interactions have 

 not been reported in the waters adjacent to Prince 

 William Sound. One encounter with killer whales was 

 reported off Kodiak Island during this study but no 

 depredation occurred. Whales probably learned to 

 depredate longline-caught fish by long-term exposure 

 to fishing activities. Accounts of killer whales feed- 

 ing off the discard of fish-processing vessels for a 

 period of over 30 days has been noted in the Bering 

 Sea (Dahlheim, unpubl. data). Active depredation 

 may begin once the whales learn to associate fishing 

 operations with a feeding opportunity. 



An examination of the yearly catch data suggested 

 that killer whales depredate 39-69% of the Green- 

 land turbot, 14-60% of the sablefish, and 6^2% of 

 the arrowtooth flounder. Whales took the largest fish 



for each species consumed. Although available, fish 

 species not eaten by killer whales included Pacific 

 cod, grenadier, rockfish, walleye pollock, and short- 

 spine thornyhead. Little is known of the food habits 

 of Bering Sea killer whales. The fish species con- 

 sumed by the whales during this study have not been 

 previously reported in the diet of North Pacific killer 

 whales (Rice, 1968), perhaps because few stomachs 

 were examined. 



Within- and between-year comparisons of catch 

 rates of sablefish, Greenland turbot, and arrowtooth 

 flounder showed that fewer fish were landed when 

 killer whales were present. Although annual changes 

 in fish biomass and composition by region have been 

 reported (Yano 4 - 5 ; Sasaki and Yano 18 ), catch rates (for 



18 Sasaki, T., and K. Yano. 1990. Report on Japan-U.S. joint 

 longline survey by Tomi Maru No. 88 in the eastern Bering 

 Sea, Aleutian Region, and Gulf of Alaska, 1988. National Re- 

 search Institute of Far Seas Fisheries, 5-7-1 Orido, Shimizu, 

 Shizuoka 424 Japan, 163 p. 



