FISHERY BULLETIN: VOL. 85, NO. 3 



growth rates are usually positively correlated 

 with temperature over the normal temperature 

 range. Growth rate for larval walleye pollock in 

 the Gulf of Alaska (0.21 mm d"^) is considerably 

 lower than that determined for larvae of the same 

 size range (4-25 mm SL) collected in the south- 

 eastern Bering Sea in June-July 1979 (0.35 mm 

 d"\ Walline 1985). Water temperatures were 

 similar in both studies (about 6°-8°C). Maximum 

 growth determined for larvae collected in the 

 Bering Sea in March-June 1980 while water tem- 

 perature was much cooler (2°-6''C), was 0.22 mm 

 d~^ (Clarke 1984). Thus differences in growth 

 rates of larval walleye pollock in the Bering Sea 

 could be due to differences in water temperature, 

 food availability, or a variety of other factors 

 which may affect growth in larvae (Bailey and 

 Stehr 1986). Future research on growth variabil- 

 ity in the field should take into account prey 

 availability, temperature, and size-specific mor- 

 tality rates. 



SUMMARY 



1. Walleye pollock in the Gulf of Alaska form an 

 intense spawning aggregation in Shelikof 

 Strait in late winter that produces a dense 

 patch of planktonic eggs in early April. Larvae 

 from this spawning can be followed as they 

 develop and are carried by currents to the 

 southwest during spring. 



2. In late May 1981, the density of larvae in this 

 patch OlO m"'^) suggested that density- 

 dependent effects on growth and survival 

 might be expected. A field study of larvae in 

 late May 1983 found maximum densities of 

 only 1 larva m '^, and investigated growth and 

 vertical distribution, and feeding in the patch. 



3. The larvae were concentrated vertically be- 

 tween about 15 and 50 m, and tended to be in 

 the upper part of this range during night and 

 early morning, whereas they were deeper dur- 

 ing the afternoon and evening. 



4. Larvae <10 mm fed primarily on copepod 

 nauplii, with copepodids becoming more im- 

 portant in larvae up to 20 mm. Copepodids of 

 Pseudocalanus spp. made up a large fraction of 

 the diet of larvae >10 mm. Most feeding oc- 

 curred during daylight. 



5. The copepods Pseudocalanus spp., Neocalanus 

 spp., Calanus spp., Oithona spp., and Acartia 

 spp. dominated the net zooplankton samples 

 (253 |jLm mesh net). 



6. Growth, based on otolith increments counted 



on 109 larvae (6.0-14.6 mm) was linear (0.21 

 mm/day, intercept = 4.29 mm, r^ = 0.75). 

 Growth rates in the area of high abundance 

 were generally not significantly different from 

 those elsewhere. 

 7. While at the larval densities observed in 1981, 

 density-dependent effects are possible, at the 

 lower densities we observed in 1983 no such 

 effects were expected or indicated in growth 

 rates or diet. Future studies should include 

 direct measurement of copepod naupliar pro- 

 duction rates in the areas inhabited by the 

 larvae. 



ACKNOWLEDGMENTS 



We wish to thank the officers, crew, and scien- 

 tific staff aboard the NO A A ship Chapman for 

 making the field work associated with this study 

 both pleasant and productive. We thank Beverly 

 Vinter, Jay Clark, and Darlene Blythe of 

 NWAFC for their help in various stages of this 

 study: converting animals in vials to data in the 

 computer and our scribblings into typescript. 

 Suam Kim, University of Washington, kindly 

 helped analyze the hydrographic data. J. J. Gov- 

 oni, NMFS Beaufort, NC; R. T. Cooney, Univer- 

 sity of Alaska, Fairbanks; and A. J. Paul, Univer- 

 sity of Alaska, Seward, provided excellent, 

 thought-provoking reviews of an earlier draft of 

 this paper. 



LITERATURE CITED 



Bailey, K M , and C L Stehr 



1986. Laboratory studies on the early life history of the 

 walleye pollock, Theragra chalcogramma (Pallas). J. 

 Exp. Mar. Biol. Ecol. 99:233-246. 



BOEHLERT, G. W., AND M M. YOKLAVICH 



1983. Effects of temperature, ration, and fish size on 

 growth of juvenile black rockfish. Sebastes 

 melanops. Environ. Biol. Fishes 8:17-28. 



Clarke. M E 



1978. Some aspects of the feeding ecology of larval walleye 

 pollock, Theragra chalcogramma in the southeastern 

 Bering Sea. M.S. Thesis, Univ. Alaska, Fairbanks, 44 



P- 



1984. Feeding behavior of larval walleye pollock, 

 Theragra chalcogramma (Pallas) and food availability to 

 larval pollock in the southeastern Bering Sea. Ph.D. 

 Thesis, Univ. California, San Diego, 208 p. 



COONEY, R T., AND K. O COYLE. 



1982. Trophic implications of cross-shelf copepod 

 distributions in the southeastern Bering Sea. Mar. Biol. 

 70:187-196. 



CooNEY, R T., T S. English, and T. Nishiyama 



1978. Upper trophic level ecology with emphasis on 

 juvenile pollock in the southest Bering Sea. In 

 PROBES: Processes and resources of the Bering Sea 

 shelf, p. 241-405. Prog. Rep. 1978. 



CUSHING, D H 



1983. Are fish larvae too dilute to affect the density of 



520 



