Abstract. —Approximately 12,396 

 Pacific cod, Gadus maerocephalus, 

 were tagged and released from fish- 

 ery research vessels in the eastern 

 Bering Sea and adjacent waters 

 between 1982 and 1990. Recapture 

 data from 373 tags recovered 

 through the first quarter of 1992 re- 

 vealed a strong seasonal component 

 in fish movement between summer 

 and winter areas. Prespawning fish 

 were tagged throughout their sum- 

 mer distribution, primarily over the 

 inner and middle shelf (<30-100 m 

 depths), and recaptured on the outer 

 shelf ( > 100-200 m ) and upper conti- 

 nental slope (>200 m) in subsequent 

 quarters. Recoveries from the win- 

 ter quarter (January-March) 

 showed the most directed movement, 

 when Pacific cod aggregated in ma- 

 jor spawning areas between Unalas- 

 ka and Unimak islands in the east- 

 ern Aleutian Islands, seaward of the 

 Pribilof Islands along the shelf edge 

 in the eastern Bering Sea, and near 

 the Shumagin Islands in the west- 

 ern Gulf of Alaska. By early summer, 

 a hypothesized postspawning dis- 

 persal was observed from these over- 

 wintering areas, when tagged Pacific 

 cod moved from deep off-shelf waters 

 to shallower depths on the eastern 

 Bering Sea shelf. The importance of 

 seasonal migration was examined 

 statistically by contingency table 

 analysis, which indicated that sea- 

 son of recovery affected area of re- 

 covery more than either the season 

 or area of tagging. Seasonal move- 

 ments were further quantified by 

 modeling the population dynamics of 

 tagged individuals, which allowed 

 estimation of the seasonal distribu- 

 tion in the eastern Bering Sea popu- 

 lation. These estimated seasonal dis- 

 tributions compare well with the sea- 

 sonal distribution of catches from the 

 commercial fisheries. This analysis 

 of tag-recapture data suggests a 

 single winter spawning population 

 in the eastern Bering Sea, nearby 

 waters of the Aleutian Islands, and 

 western Gulf of Alaska waters be- 

 tween longitude 157°W and 170°.W 



Seasonal movements of Pacific cod, 

 Gadus maerocephalus, in the 

 eastern Bering Sea and adjacent 

 waters based on tag-recapture data 



Allen M. Shimada 



Alaska Fisheries Science Center 



National Marine Fisheries Service. NOAA 



7600 Sand Point Way NE. Seattle, Washington 98 1 I 5-0070 



Present address. Office of Research and Environmental Information 



National Marine Fisheries Service, NOAA 



1335 East-West Highway. Silver Spring, Maryland 20910 



Daniel K. Kimura 



Alaska Fisheries Science Center 



National Marine Fisheries Service, NOAA 



7600 Sand Point Way NE, Seattle, Washington 98 1 1 5-0070 



Manuscript accepted 6 April 1994. 

 Fishery Bulletin 92:800-816. 



800 



Pacific cod, Gadus maerocephalus, 

 are widely distributed throughout 

 the North Pacific Ocean. Off North 

 America, Pacific cod range from 

 California north through British 

 Columbia and southeast Alaska, 

 into the Bering Sea, and west along 

 the Aleutian Islands (Bakkalaetal., 

 1984). Pacific cod are found epiben- 

 thically over the Bering Sea shelf 

 and slope. The Bering Sea repre- 

 sents the center of greatest regional 

 abundance, although Pacific cod are 

 also abundant in the neighboring 

 Aleutian Islands and Gulf of Alaska 

 waters (OCSEAP, 1987). Pacific cod 

 catches rank third among the east- 

 ern Bering Sea groundfish resources 

 following walleye pollock, Theragra 

 chalcogramma, and yellowfin sole, 

 Pleuronectes asper (Low, 1991 ). 



Beginning in the early 1980's, 

 Pacific cod catches increased sub- 

 stantially above the 10,000 to 

 50,000 metric tons (t) landed annu- 

 ally between 1958 and 1979. East- 

 ern Bering Sea and Aleutian Islands 

 catches over the last decade have 

 averaged 132,500 t; a historic high 



of 198,000 t was taken in 1988 

 (Thompson, 1994). Much of this 

 growth was due to the recruitment 

 of exceptionally strong 1977-78 

 year classes, in combination with 

 greater fishing effort from joint- 

 venture (i.e. U.S. fishing vessels de- 

 livering catches to foreign proces- 

 sors at sea) and new domestic 

 groundfish fisheries (Bakkala, 1984; 

 Shimada, 1985). More recently, the 

 eastern Bering Sea and Aleutian Is- 

 lands Pacific cod fishery generated 

 a catch of 177,300 t, valued at $90 

 million in 1991 (NMFS, 1992). 

 These developments in resource 

 availability and in expanding fish- 

 ery exploitation patterns provided 

 the impetus for new studies into the 

 biology of Pacific cod in Alaskan 

 waters. 



In September 1982, a pilot tag- 

 ging experiment for Pacific cod and 

 walleye pollock in the eastern 

 Bering Sea was conducted by Na- 

 tional Marine Fisheries Service 

 (NMFS) scientists from the Alaska 

 Fisheries Science Center (AFSC). 

 The initial objective of this experi- 



