368 



Fishery Bulletin 93(2). 1995 



n = 31339 



» 600 



c 



e 



E 

 u 

 O 



a 400 



B 



n = 3410 





n:91 



I 



1 



501 601 701 



Fork length (mm) 



Figure 8 



Length-frequency distribution of sablefish, Anoplopoma fimbria. 

 (A) All areas (see Fig. 1); (B) all stations fished where depreda- 

 tion occurred; (C) calculated length (head length and maxillary 

 length) of partially consumed fish. 



the 10-year period) were typically lower when killer 

 whales were reported as present. 



Depredation rates based on average catch rates 

 (REY and RE A values) were higher than those cal- 

 culated from direct counts of damaged fish (RNT and 

 RNS values). Calculated values of RNT and RNS did 

 not consider empty hooks. It is possible that parts of 

 the fish that were preyed upon were pulled off or 

 dropped off the line as it was being retrieved. Thus 

 the rate of predation based on a direct-count method 

 may underestimate the overall rate of depredation. 

 However, RNT and RNS values were used as direct 

 evidence of depredation by killer whales. RNS val- 

 ues indicated that killer whales actively depredate 

 at least 22% of the sablefish, 45% of Greenland tur- 

 bot, and 13% of the arrowtooth flounder. Large num- 

 bers of arrowtooth flounder are found in shallower 



depths where killer whales do not actively prey on 

 fish, but sablefish and Greenland turbot are found 

 in deeper depths where active depredation has been 

 observed (Yano 4 ). However, a greater number of dam- 

 aged arrowtooth flounder prevailed in the catch 

 (higher RNS values). Depredation rates by killer 

 whales on the U.S. domestic Bering Sea fishery could 

 easily be higher because some vessels (due to overall 

 size and limited range) are forced to fish repeatedly 

 in the same area. If a particular area is in a region of 

 high killer whale density, the vessel may experience 

 continual problems. Reports of killer whales follow- 

 ing vessels over short distances from one fishing area 

 to another have been documented (Onodera 19 ). 



19 Onodera, S. Fishing master ofTomi Maru No. 88, 6-3-25 Irifune, 

 Kushiro, Hokkaido 085 Japan. Personal commun., October 1988. 



