STOMACH CONTENTS AND FOOD CONSUMPTION ESTIMATES OF 

 PACIFIC HAKE, MERLUCCIUS PRODUCTUS 1 



Eric A. Rexstad 2 and Ellen K. Pikitch 3 



ABSTRACT 



Analysis of 466 stomachs of Pacific hake, Merluccius productus, collected during August 1983 off the 

 coasts of Washington and Oregon indicates euphausiids comprise the most important food resource in 

 terms of percent by weight, numbers, and frequency of occurrence for the species at that time of year. 

 The importance of fish in the Pacific hake diet increases with the size of the hake, constituting 87% of 

 the diet by weight in the largest individuals. Weak evidence of a nocturnal feeding pattern was observed. 

 This indistinct nocturnal feeding pattern could have been caused by poor food availability due to El Nino. 

 Estimates of food consumption by Pacific hake indicate that this species may have a substantial impact 

 on some commercially valuable species such as pink shrimp, Pandalus jordani, even though pink shrimp 

 is a fairly minor component of the diet. A statistically significant negative relationship between Pacific 

 hake catch-per-unit-effort (CPUE) and pink shrimp CPUE off the west coast of the United States, using 

 a lag of 2 years, was found. 



Pacific hake, Merluccius productus, constitute an 

 important component of the California Current 

 ecosystem off the west coast of North America. 

 It is estimated that a standing stock of approx- 

 imately 1.5 million metric tons (t) exists off the 

 Pacific coast between central California and Van- 

 couver Island (Bailey et al. 1982). This biomass 

 represents a substantial prey base for a variety of 

 fish in the ecosystem: great white sharks, Car- 

 charodon carcharias; soupfin sharks, Galeorhinus 

 zyopterus; Pacific electric ray, Torpedo californica; 

 bonito, Sarda chiliensis; albacore, Thunnus 

 alalunga; bluefin tuna, Thunnus thynnus; rock- 

 fishes, Sebastes spp.; sablefish, Anoplopoma fimbria; 

 lingcod, Ophiodon elongatus; dogfish, Squalus acan- 

 thias; and arrowtooth flounder, Atheresthes stomias 

 (Bailey et al. 1982). Pacific hake also constitute a 

 major prey item for a number of marine mammals, 

 including the California sea lion, Zalophus califor- 

 nianus; northern sea lion, Eumetopias jubatus; 

 northern fur seal, Callorhinus ur sinus; saddleback 

 dolphin, Delphinus delphis; Pacific whiteside 

 dolphin, Lagenorhynchus obliquidens; and northern 

 right whale dolphin, Lissodelphis borealis (Fiscus 

 1979). 



'Technical paper No. 7718, Oregon Agricultural Experimental 

 Station. 



department of Fisheries and Wildlife, Hatfield Marine Science 

 Center, Oregon State University, Newport, OR 97365; present 

 address: Colorado Cooperative Fish and Wildlife Research Unit, 

 Department of Fishery and Wildlife Biology, Colorado State 

 University, Ft. Collins, CO 80523. 



department of Fisheries and Wildlife, Hatfield Marine Science 

 Center, Oregon State University, Newport, OR 97365. 



Pacific hake also have an important impact on 

 species below them in the food chain. Best (1963) 

 described Pacific hake as opportunistic feeders. 

 Their diet includes numerous species of Crustacea, 

 particularly euphausiids, several genera of shrimp, 

 crab megalopae, and a variety of fish including 

 Pacific herring, Clupea harengus pallasi; rockfish; 

 sablefish; and flatfish (Livingston 1983). Pacific hake 

 may compete for food resources with a host of other 

 species that feed on the abundant euphausiid 

 resource (Tyler and Pearcy 1975; Karpov and 

 Cailliet 1978; Brodeur and Pearcy 1984), including 

 commercially prized salmonids (Peterson et al. 

 1982). 



At the top of the trophic structure is the commer- 

 cial fishing fleet, comprised mainly of foreign joint- 

 venture fishing boats that have harvested, on 

 average, 127,000 t of Pacific hake per year since 

 1966 (R. C. Francis 4 ). 



Pacific hake migrate seasonally along the west 

 coast of North America (Swartzman et al. 1983) and 

 spawn in winter in the warm waters off southern 

 California and the Baja peninsula. During the spring 

 and summer, the adults migrate as far north as Van- 

 couver Island to feed. The Pacific hake tend to 

 stratify along the coast by size, with the largest in- 

 dividuals traveling farthest from the spawning areas 

 and smaller juveniles remaining off the coast of 

 California. In autumn, the adults return to the south- 

 ern spawning areas (Bailey et al. 1982). 



4 R. C. Francis, Fisheries Research Institute, University of Wash- 

 ington, Seattle, WA 98195, pers. commun. May 1985. 



Manuscript accepted July 1986. 



FISHERY BULLETIN: VOL. 84, NO. 4, 1986. 



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