DISTRIBUTION, FEEDING, AND GROWTH OF LARVAL WALLEYE 

 POLLOCK, THERAGRA CHALCOGRAMMA , FROM SHELIKOF STRAIT, 



GULF OF ALASKA 



A. W. Kendall, Jr .^ M. E. Clarke,^ M. M. Yoklavich,^ 



AND G. W. BOEHLERT"* 



ABSTRACT 



Walleye pollock in the Gulf of Alaska have recently been found to form an intense spawning 

 aggregation in late winter in Shelikof Strait. This produces a dense patch of planktonic eggs in early 

 April, and later in spring a patch of larvae that can be followed as it drifts to the southwest. The 

 density of larvae observed in 1981 indicated that density-dependent effects on feeding may be 

 important for larval survival. In May 1983 we conducted a field study to investigate spatial and 

 vertical distribution, feeding, and growth of larvae from this spawning. During this study we found, 

 in an area of maximum concentration (-1 larva m"3) located by an initial survey, larvae averaged 

 11.1 mm SL, and were similar in size to those found elsewhere. The larvae in 1983 were larger, and 

 less abundant than at the same time in 1981. Larval growth was estimated from the number of otolith 

 daily growth increments at size of larva and was similar in the area of maximum concentration and 

 in other areas. Larvae were concentrated vertically between about 15 and 50 m and showed a 

 crepuscular pattern of increased density at 14-28 m during twilight. Neither the vertical nor 

 horizontal patterns of larval occurrences seemed closely associated with particular values of 

 temperature or salinity. Most larvae were found in a temperature range of 7.0°-5.5°C and a salinity 

 range of 31. 5-32. 29??. Guts of larvae collected during darkness contained less food than those from 

 daytime. Copepod nauplii were largely replaced by Pseudocalanus spp. copepodids in the diet of larvae 

 larger than 14 mm. At the densities of walleye pollock larvae observed in this study, it appears that 

 zooplankton production in the area did not impact larval growth, even in the area of maximum 

 density. 



A large spawning concentration of walleye pol- 

 lock, Theragra chalcogramma, was discovered in 

 1980 in Shelikof Strait, and subsequently a 

 220,000 metric ton/year fishery developed. Shel- 

 ikof Strait, a 50 by 200 km body of water in the 

 northern Gulf of Alaska, between the Kodiak 

 Archipelago and the Alaska Peninsula, is appar- 

 ently the major spawning center for Gulf of 

 Alaska walleye pollock. Ichthyoplankton surveys 

 in 1981 and 1982 showed that spawning occurs 

 primarily in a restricted area within Shelikof 

 Strait and over a short period of time, producing 

 a dense patch of eggs. Thereafter, larvae drift 

 southwest with prevailing currents (Fig. 1). The 



iNorthwest and Alaska Fisheries Center, National Marine 

 Fisheries Service, NOAA, 7600 Sand Pomt Way, N.E., Building 

 4, BIN C15700, Seattle, WA 98115. 



2Rosenstiel School of Marine and Atmospheric Sciences, 

 University of Miami, Miami, FL 33149. 



^Cooperative Institute for Marine Resources Studies, Oregon 

 State University, Marine Science Center, College of 

 Oceanography, Newport, OR 97365. 



■^Southwest Fisheries Center Honolulu Laboratory, National 

 Marine Fisheries Service, NOAA, 2570 Dole Street, Honolulu, 

 HI 96822-2396. 



densities of walleye pollock eggs and early larvae 

 found in Shelikof Strait in 1981 exceeded 50 m"*^ 

 (Dunn et al. 1984^), far greater than their densi- 

 ties in the Bering Sea (Kim and Kendall 1983^) or 

 Funka Bay, Japan (Hayashi et al. 1968); more- 

 over, these densities significantly exceed those 

 reported for larvae of any other fish (Hempel 

 1979). 



Energetic requirements of larvae in high densi- 

 ties may exceed production of food and possibly 

 lead to density-dependent effects on larval growth 

 and survival (Jones 1973). At larval densities fre- 

 quently found (ca. 1 m""^), density-dependent ef- 

 fects are not considered important (McGowen and 

 Miller 1980; Gushing 1983). Laboratory studies, 

 however, have demonstrated effects of stocking 



5Dunn, J. R., A. W. Kendall, Jr., and R. D. Bates. 1984. 

 Distribution and abundance patterns of eggs and larvae of 

 walleye pollock (Theragra chalcogramma) in the western Gulf 

 of Alaska. NWAFC Proc. Rep. 84-10, 66 p. 



6Kim, S., and A. W. Kendall, Jr. 1983. The numbers and 

 distribution of walleye pollock eggs and larvae in the 

 southeastern Bering Sea. U.S. Dep. Commer., Natl. Mar. Fish. 

 Serv., NOAA, NWAFC Proc. Rep. 83-22, 35 p. 



Manuscript accepted March 1987. 

 FISHERY BULLETIN: VOL 85, NO 3, 



1987. 



499 



