Abstract. Eggs of walleye 



pollock, Theragra chalcogramma, 

 from Shelikof Strait, Alaska, were 

 reared at three temperatures: 3.8°, 

 5.7°, and 7.7°C. Development was 

 divided into 21 stages. A piece- 

 wise regression model with mid- 

 points of each stage describes the 

 relation between time to each 

 stage of development and tempera- 

 ture. Preserved eggs of each stage 

 are described, illustrated, and pho- 

 tographed. Midpoint of hatch was 

 393 hours at 3.8°C, 303 hours at 

 5.7°C, and 234 hours at 7.7°C. 

 Mean length of larvae at hatch in- 

 creased linearly with temperature. 

 We compared rate of develop- 

 ment, time to 50% hatch, and mor- 

 phological development with other 

 studies of walleye pollock eggs. 

 Rate of development and time to 

 50% hatch were similar among 

 populations of eastern North Pa- 

 cific walleye pollock. Western 

 North Pacific walleye pollock re- 

 quired longer incubation times 

 than eastern North Pacific walleye 

 pollock. Morphological develop- 

 ment of Shelikof Strait eggs differs 

 from development of western 

 North Pacific walleye pollock eggs: 

 optic vesicles, myomeres, eye 

 lenses, heart, and otic capsules 

 appear earlier than in Shelikof 

 Strait eggs, and eye pigment ap- 

 pears later. The differences in de- 

 velopment may be exacerbated by 

 the condition of the eggs in which 

 they were examined (e.g. pre- 

 served vs. live). Developmental 

 differences between stocks are dis- 

 cussed with the conclusion that 

 model components for egg mortal- 

 ity and spawning biomass must be 

 based on specimens collected in 

 the area of interest. 



Embryonic development of 



walleye pollock, 



Theragra chalcogramma, 



from Shelikof Strait, Gulf of Alaska* 



Deborah M. Blood 

 Ann C. Matarese 

 Mary M. Yoklavich** 



Alaska Fisheries Science Center, National Marine Fisheries Service. NOAA 

 7600 Sand Point Way N.E., Seattle, WA 981 15-0070 



Walleye pollock, Theragra chalco- 

 gramma, is the most abundant 

 member of the family Gadidae in 

 the subarctic Pacific Ocean and 

 Bering Sea, supporting the largest 

 single-species commercial fishery 

 in the world (Megrey, 1991). In 

 the Gulf of Alaska, Shelikof Strait 

 is the principal spawning area 

 (Kendall and Picquelle, 1990) and 

 has been the site of intensive re- 

 search to understand processes 

 leading to recruitment variability 

 of walleye pollock (Schumacher and 

 Kendall, 1991). 



Age determination of fertilized 

 eggs is a basis for investigating 

 biotic and abiotic impacts on the 

 earliest life-history stage and thus 

 for understanding interannual 

 variability in walleye pollock re- 

 cruitment. Age of walleye pollock 

 eggs has been crucial to several 

 studies. Egg mortality and spawn- 

 ing biomass are estimated by mod- 

 eling age-specific egg abundance 

 over time (Picquelle and Megrey, 

 1993; Bates 1 ). Patterns in horizon- 

 tal or vertical distribution and 

 abundance of walleye pollock eggs 

 in the western Gulf of Alaska have 

 been described by grouping devel- 



opmental stages into broad age 

 groups (Kendall and Kim, 1989; 

 Kendall and Picquelle, 1990). 



Egg age is an independent vari- 

 able in the models used to estimate 

 egg production and mortality. 

 Therefore, increasing the accuracy 

 in measuring egg ages should im- 

 prove estimates of these values. In 

 past studies, walleye pollock eggs 

 have been incubated in the labora- 

 tory to develop temperature-spe- 

 cific equations that estimate dura- 

 tion of development or age of the 

 eggs, to describe morphological de- 

 velopment, to observe effects of 

 light on egg buoyancy and hatching 

 rate, and to obtain larvae for ex- 

 periments (Table 1). Although 

 these incubation studies provide 

 pertinent data on ontogeny of wall- 

 eye pollock, none can be used with 

 accuracy to determine age of eggs 



Bates, R. D. 1987. Estimation of egg pro- 

 duction, spawner biomass, and egg mor- 

 tality for walleye pollock, Theragra 

 chalcogramma, in Shelikof Strait from 

 ichthyoplankton surveys during 1981. 

 U.S. Dep. Commer., NOAA, Nat. Mar. 

 Fish. Serv., Northwest Alaska Fish. Cent., 

 7600 Sand Point Way N.E., Bin C15700, 

 Bldg. 4, Seattle, WA 98115-0070. Proc. 

 Rep. 87-20, 192 p. 



Manuscript accepted 3 November 1993 

 Fishery Bulletin 92: 207-222 (1994) 



* Contribution 0148 of the Fisheries Oceanography Coordinated Investigations, NOAA, 



Seattle. 

 ** Present address: Southwest Fisheries Science Center, Pacific Fisheries Environmen- 

 tal group. National Marine Fisheries Service, NOAA, P.O. Box 831, Monterey, CA 93942 



207 



