SUMMER FOOD OF THE PACIFIC COD, 



GADiS MACROCEPHALLS. 

 NEAR KODIAK ISLAND, ALASKA 



1,2.3 



The Pacific cod, Gadiis macrocephalus Tilesius, 

 was the target of the earliest United States com- 

 mercial fishery in the North Pacific (Buck'*). Its 

 fleet, organized in spring 1865 (Bean 1887), began 

 to fish along the Alaska Peninsula and the Aleu- 

 tian Islands and eventually expanded into the 

 Bering Sea (Cobb 1916). Dwindling stocks and 

 poor market prices ultimately resulted in the col- 

 lapse of this fishery shortly after World War II 

 (Ketchen 1961). 



Growing pressures in recent years on domestic 

 fishing stocks, in addition to increased worldwide 

 protein demand, improved technological skills 

 and readily available investment capital, have re- 

 sulted in renewed interest in Pacific cod in the 

 United States (Jones 1977). A bottomfish survey 

 off the coast of Kodiak Island and throughout 

 Shelikof Strait by the National Marine Fisheries 

 Service in 1973 showed the Pacific cod to be one of 

 the most abundant fishes inhabiting the area and 

 the standing stock was conservatively estimated 

 to be about 36,363 t (Hughes and Parks 1975). A 

 small experimental trawl fishery for the Pacific 

 cod and other bottom fishes has been proposed for 

 the Kodiak region by Jones (1977). 



Preliminary examination of G. macr^ocephalus 

 stomach contents by Alaska Department of Fish 

 and Game (ADF&G) biologist Guy C. Powell and 

 the author during ADF&G crab investigations off 

 Kodiak Island indicated a high frequency of oc- 

 currence of the commercially important snow 

 crab, Chionoecetes bairdi. In view of the probable 

 predation pressure on existing snow crab popula- 

 tions by G. macrocephalus and in view of the po- 

 tential commercial importance of the Pacific cod, 

 the summer food habits of this fish in the Kodiak 

 area were examined by me. Ancillary goals in- 

 cluded a comparison of food data from pot- and 

 trawl-captured cod. 



'Contribution No. 339, Institute of Marine Science, University 

 of Alaska, Fairbanks, AK 99701. 



^This study was partially supported under contract 03-5-022- 

 56 between the University of Alaska and NOAA, U.S. Depart- 

 ment of Commerce through the Outer Continental Shelf En- 

 vironmental Assessment Program to which funds were provided 

 by the Bureau of Land Management, U.S. Department of In- 

 terior. 



■'Based on a thesis submitted in partial fulfillment of the re- 

 quirements for the M.S. degree. University of Alaska 



■•Buck.E. H. 1973. Alaska and the law of the sea. National 

 patterns and trends of fishery development on the North Pa- 

 cific. Alaska Sea Grant Rep. No. 73-4, 65 p. 



700 



Methods 



Specimens were taken near Kodiak Island, 

 Alaska, (Figure 1) in conjunction with the crab- 

 assessment studies of ADF&G and the surveys of 

 the International Pacific Halibut Commission. 

 Fishing gear consisted of commercial king crab 

 pots, measuring 203 x 203 x 76 cm (inside) and 

 weighing 340 kg; baited with chopped, frozen her- 

 ring. Webbing was #72 tarred nylon thread with 

 mesh stretched to 7.6 cm. The gear used on the 

 halibut-survey vessels in July 1975 and July 1976 

 was a standard 400-mesh Eastern otter trawl 

 (Greenwood 1958). Sampling by pots was from 26 

 June to 3 August 1973, 28 June to 31 July 1974, 

 and 30 June to 27 July 1975. Stations usually 

 consisted of 4-12 pots in a straight line, equally 

 spaced every 0.46 km. Gear was pulled every 18-24 

 h except when weather conditions prolonged 

 fishing time. 



A haphazard sample of 3,933 of Pacific cod was 

 taken from 10,857 cod caught in pots (the number 

 sampled was contingent on the shipboard time 

 available for analysis of stomach contents). Food 

 items were identified to the lowest taxon practical 

 aboard ship, and unidentifiable contents were pre- 

 served for later laboratory examination. Analysis 

 of stomach contents was carried out using the fre- 

 quency of occurrence method in which the prey 

 organisms are expressed as the percent of 

 stomachs containing various food items from the 

 total number of stomachs analyzed. Cod were ar- 

 bitrarily divided into 33-52 cm, 53-72 cm, and 

 73-92 cm size (total length) groups for analysis. 

 The frequency of occurrence method was also 

 used for food data from trawl-caught Pacific cod. 

 The stomachs of 344 cod were examined from 24 

 trawl stations, which were located in the same 

 general area as the pot stations (Figure 1). 



Results and Discussion 



As determined from the pot data, the summer 

 diet of G. macrocephalus was fishes, crabs, 

 shrimps, and amphipods, in decreasing order of 

 occurrence (Table 1). The most frequently occur- 

 ring fish was walleye pollock, Theragra chalco- 

 gramma. Flatfishes (Pleuronectidae) and Pacific 

 sand \a.nce, A in modytes hcxapterus, were also fre- 

 quent. Suyehiro (1942:233-236), Moiseev (1953, 

 1960), and Mito (1974) also reported that Pacific 

 cod feed on these fishes. 



