REXSTAD and PIKITCH: FOOD CONSUMPTION OF PACIFIC HAKE 



summer of 1967. From 204 stomachs collected dur- 

 ing the 1980 NMFS West Coast Groundfish Survey 

 off the coasts from Oregon to Vancouver Island, 

 Livingston (1983) found pink shrimp constituted 

 0.7% by weight of the Pacific hake diet. Pink shrimp 

 occurred in 1.7% of the Pacific hake stomachs col- 

 lected in the study described in this paper. Thus, 

 with the exception of Gotshall's work, studies of the 

 food habits of Pacific hake have shown pink shrimp 

 generally comprise well under 10% of the Pacific 

 hake diet, and thus do not appear to be an impor- 

 tant food source for hake. However, due to the large 

 biomass of Pacific hake in the North Pacific, it is 

 possible that Pacific hake may represent a signifi- 

 cant source of mortality even for those species, in- 

 cluding pink shrimp, that are not significant com- 

 ponents of the Pacific hake diet (Francis 1983). 



The estimated consumption of 659.3 t/season of 

 pink shrimp compares with a commercial catch of 

 2,197 1 of pink shrimp landed in Oregon during 1984 

 by 59 vessels (Saelens and Zirges 1985). It is con- 

 ceivable that the magnitude of Pacific hake preda- 

 tion on pink shrimp may increase in the near future. 

 Small Pacific hake, preying mainly on euphausiids, 

 constituted the bulk of the consumers in this study. 

 The strong 1980 year class of Pacific hake, seen as 

 the 35-39 cm size class in these 1983 data, will have 

 substantially greater impact on commercially valu- 

 able species upon reaching larger sizes when these 

 valuable species comprise a larger fraction of the 

 diet. 



Francis (1983) inferred, from catch statistics of 

 Pacific hake and pink shrimp, that increased catches 

 of Pacific hake since the inception of the foreign and 

 subsequent joint- venture fisheries may have con- 

 tributed to the dramatic increase in the landings of 

 pink shrimp during the late 1970s. The causal 

 mechanism inferred is the release of predation 

 pressure on the pink shrimp population as a result 

 of decreased Pacific hake abundance due to fishing. 

 This "surplus" in the pink shrimp population was 

 harvested by the increasingly vigorous shrimp 

 fishery. 



This contention is disputed by Livingston and 

 Bailey (1985). Their analysis focuses on pink shrimp 

 CPUE during two time periods: 1952-65 during 

 which Pacific hake were unexploited and 1966-77 

 during which a substantial joint-venture fishery 

 occurred. They found no appreciable change in aver- 

 age pink shrimp CPUE between the two periods. 

 Extending their analysis to include the most recent 

 catch statistics, we also fail to find the existence of 

 a significant difference between the periods 1957-65 

 and 1966-84 (t = 1.05, 26 df, P = 0.303). 



However, if pink shrimp have constituted a fair- 

 ly constant proportion of the Pacific hake diet over 

 time, as suggested by this and previous Pacific hake 

 food habit studies, then there may indeed be a rela- 

 tionship between the release of predator pressure 

 by the Pacific hake and increased catches of pink 

 shrimp. The regression-correlation analysis pre- 

 sented above has an advantage over the average 

 pink shrimp CPUE analysis because it incorporates 

 information about both hake and shrimp abun- 

 dances. The regression-correlation results provide 

 weak statistical support to Francis' contention that 

 there is a relationship between Pacific hake and pink 

 shrimp population dynamics. However, further ob- 

 servations are needed to obtain greater confidence 

 in this relationship. In particular, it will be interest- 

 ing to note that the impact of the strong 1980 year 

 class Pacific hake on pink shrimp catches in the near 

 future. 



CONCLUSION 



Pacific hake occupy a unique trophic position, 

 serving not only as predators but also as prey for 

 a variety of species carrying valuations other than 

 those of an economic nature (endangered species 

 and species managed under the Marine Mammal 

 Protection Act). Euphausiids constitute the primary 

 source of food for Pacific hake in the North Pacific. 

 However, as Pacific hake mature, euphausiids 

 decrease in importance and fish take on greater im- 

 portance. Owing to the vast quantity of hake bio- 

 mass living in the North Pacific, it has been shown 

 that Pacific hake may consume large quantities of 

 several commercially valuable species, even though 

 these species comprise a fairly small percentage of 

 the diet. It has also been demonstrated that a 

 statistically significant relationship exists between 

 CPUE of Pacific hake and pink shrimp. Additional 

 years of data are required to have a clearer under- 

 standing of this relationship. 



ACKNOWLEDGMENTS 



Bill Barss and Mark Saelens of the Oregon 

 Department of Fish and Wildlife (ODFW) assisted 

 in the collection of the Pacific hake stomachs at sea 

 and with the identification of decapods. Leslie Lutz 

 of ODFW helped with the laboratory analysis and 

 Rick Brodeur, Chris Wilson, and Bruce Mundy of 

 Oregon State University aided in the identification 

 of fish remains. Rick Brodeur also gave suggestions 

 on statistical analysis. Helpful comments were pro- 

 vided by Mac Zirges, Mark Saelens, Robert Fran- 



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