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



357 



Between 1980 and 1989, stations where killer 

 whales were present were recorded. During vessel 

 surveys in 1988, depredation rates by killer whales 

 were quantified. During the 1988 surveys, as the 

 groundline was retrieved, fish that had been dam- 

 aged or partially consumed by killer whales were iden- 

 tified by remains left on the hook (e.g. heads, lips, or 

 gills ). In addition, head length ( HL ) or maxillary length 

 (ML) measurements were collected for each damaged 

 fish. Head length (mm) was measured from the most 

 anterior point of the snout of the upper jaw to the most 

 distant point of the posterior margin of the operculum. 

 Maxillary length (mm) was measured along the long- 

 est margin on the premaxillary side. Fork length (FL) 

 for sablefish and arrowtooth flounder, Atheresthes 

 stomias, and total length (TL) for Greenland turbot 

 were also measured. Fork length and TL were mea- 

 sured from the tip of the snout to the central point of 

 the caudal fin. The relationships between HL and FL 

 or TL and between ML and FL or TL were calculated 

 by the least-square method following the equation: 



Y = a + bX, 



where Y is FL or TL (mm), X is HL or ML (mm), and 

 a and b are constants. Average lengths of damaged 

 and undamaged fish were compared by using £-tests 

 with a significance level of 0.05. 



To obtain killer whale depredation rates for each 

 station, direct counts were made of the remaining 

 heads, lips, or gills that were brought aboard the 

 research vessel. Empty hooks did not provide evi- 

 dence of killer whale depredation and were not in- 

 cluded in the analysis. 



Killer whale depredation rates were calculated by 

 two methods. RNT is the depredation rate calculated 

 from the number of fish preyed upon as a percent- 

 age of the total number of fish landed per fishing 

 trip. RNS is the depredation rate calculated from the 

 number of fish preyed upon as a percentage of the 

 number offish landed from the time the whales were 

 first observed to depredate them. 



The two depredation rates were calculated for each 

 station as 



RNT (%) = NP/(NT+NP) x 100 



and 



4 1 continued) Fisheries Resources (GSKi, Tohoku National Fish- 

 eries Research Institute. Hachinohe Branch, 25-259 Shim- 

 omekurakubo, Samemachi. Hchinohe, Aomori 031, Japan, No. 

 22, p. 145-173. [In Japanese.] 



5 Yano, K. 1990. Report on sablefish and Pacific cod resource de- 

 velopmental survey, 1988. Japan Marine Fishery Resources 

 Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 Japan, 

 JAMARC Rep. S63/No.ll, 195 p. [In Japanese.] 



RNS (%) = NP/(NS+NP) x 100, 



where NP is the number of depredated fish, counted 

 by the remaining heads, lips, or gills; NT is the total 

 number offish landed with no evidence of killer whale 

 depredation; and NS is the number of fish landed 

 without any physical evidence of depredation counted 

 from the time the whales were first observed to dep- 

 redate fish (determined by observing heads, lips, or 

 gills on the groundline). 



Other depredation rates (REA and REY) were ob- 

 tained by averaging the catch rates (number offish 

 per hachi) obtained during the 1980 and 1988 sur- 

 veys. REA is the depredation rate calculated from 

 the average catch rates for all years at each station. 

 REY is the depredation rate calculated from the av- 

 erage catch rates for all stations for each year. The 

 average catch rates (REA and REY) were obtained 

 through the following formula: 



REA or REY(%) = 100 - (AJB x 100), 



where A is the average catch rate during whale dep- 

 redation for all years at each station (for REA ) or all 

 stations for each year (for REY), and B is the aver- 

 age catch rate with no killer whale depredation for 

 all years at each station (for REA) or all stations for 

 each year (for REY). We tested for differences in the 

 average catch rates for REA and REY by using the 

 one-way analysis of variance (ANOVA). The annual 

 survey reports of the Japan Marine Fishery Re- 

 sources Research Center (JAMARC) by Inada and 

 Sasaki, 6 Onoda and Sasaki, 7 Mizogoshi and Sasaki, 8 

 Funato and Sasaki, 9 Iwami and Sasaki, 10 Fukui and 

 Sasaki, 11 Takeda and Sasaki, 12 Takeda, 13 and Yano 5 

 provided fish catch data for the study. 



6 Inada, T., and T. Sasaki. 1981. Report on sablefish and Pacific 

 cod resource developmental survey, 1980. Japan Marine Fish- 

 ery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, To- 

 kyo 102 Japan, JAMARC Rep. S55/No. 18, 156 p. [In Japanese.] 



7 Onoda, M., and T. Sasaki. 1982. Report on sablefish and Pa- 

 cific cod resource developmental survey, 1981. Japan Marine 

 Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, 

 Tokyo 1 02 Japan, JAMARC Rep. S56/No.l5, 140 p. [In Japanese.] 



8 Mizogoshi, H., and T Sasaki. 1984. Report on sablefish and 

 Pacific cod resource developmental survey, 1983. Japan Marine 

 Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, 

 Tokyo 102 Japan, JAMARC Rep. S58/No.l3, 219 p. [In Japanese.] 



9 Funato, K, and T Sasaki. 1985. Report on sablefish and Pa- 

 cific cod resource developmental survey, 1982. Japan Marine 

 Fishery Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, 

 Tokyo 102 Japan, JAMARC Rep. S57/No.l3, 191 p. [In Japanese.] 



10 Iwami, T, and T Sasaki. 1985. Report on sablefish and Pacific 

 cod resource developmental survey, 1984. Japan Marine Fishery 

 Resources Research Center, 3-27 Kioi-cho, Chiyoda-ku, Tokyo 102 

 Japan, JAMARC Rep. S59/No.l2, 223 p. [In Japanese.] 



11 Fukui, J., and T Sasaki. 1988. Report on sablefish and Pacific 

 cod resource developmental survey, 1985. Japan Marine 



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