Abstract.— Egg size has been 

 shown to relate to survival and growth 

 in the early life stages of fish. Com- 

 bined field and laboratory studies ex- 

 amined variation in the egg size of 

 walleye pollock Tlwragi-a chalcogram- 

 ma. a commercially important North 

 Pacific gadoid; and a preliminary as- 

 sessment of the effect of egg size on 

 larval size was made. Differences in 

 egg size were found over parts of the 

 geographical range, among years, 

 and over the spawning season in 

 Shelikof Strait. Egg size did not ap- 

 pear to correlate with female length, 

 age, or condition. Individual female's 

 egg size decreased significantly over 

 the course of the spawning cycle. 

 Preliminary studies in the laboratot^ 

 showed that egg size is correlated 

 with larval size and may therefore 

 affect mortality in the early larval 

 stages. 



Variation of Egg Size of Waileye 

 Pollocl< Theragra chalcogramma 

 \N\th a Preliminary Examination of 

 the Effect of Egg Size on Larval Size 



Sarah Hinckley 



Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA 

 7600 Sand Point Way NE, Seattle, Washington 981 15 



Variability in egg size may be an im- 

 portant factor in the survival of early 

 life stages of fish. It has been proposed 

 by numerous authors (Blaxter and 

 Hempel 1963, Bagenal 1969, Ware 

 1975, Hunter 1981, Knutsen and Til- 

 seth 1985) that egg size (dry weight 

 or diameter) influences larval survi- 

 val through its effects on larval size, 

 growth rates, and activity. Larger 

 eggs provide more energy for growth 

 and development (Hempel and Blax- 

 ter 1967, Hempel 1979) and general- 

 ly produce larger larvae which are 

 able to avoid predators more effec- 

 tively (Miller et al. 1988), survive 

 longer without feeding (Hunter 1981), 

 search a greater volume of water for 

 prey (Blaxter 1986, Webb and Weihs 

 1986), and eat prey of a greater vari- 

 ety of sizes (Hunter 1981). 



Differences in egg size are thought 

 to reflect adaptations by the spawn- 

 ing stock to varying conditions met 

 by early larvae. Bagenal (1971) pro- 

 posed that there is a relationship 

 among egg size, time of spawning, 

 and availability of food. Gushing (1967) 

 stated that egg size in Atlantic her- 

 ring Clupea harengus harengus is re- 

 lated to the type of production cycle 

 and its variability. 



Hunter (1976) indicated that egg 

 size may be important in studies of 

 starvation and predation as cause of 

 larval fish mortality, because of its ef- 

 fects on time to the onset of irrever- 

 sible starvation, on feeding success. 



Manuscript accepted 26 April 1990. 

 Fishery Bulletin, U.S. 88:471-483. 



•Contribution FOCl-0078 to Fisheries-Ocean- 

 ography Coordinated Investigations, NOAA. 



and on the ability of larvae to avoid 

 predators. Larval size and its relation 

 to egg size has been proposed as a 

 unifying factor integrating the dynam- 

 ics of larval survival and the mechan- 

 isms of recruitment. Miller et al. 

 (1988), in their review of this subject, 

 state that "... even small size differ- 

 ences of larvae at hatching can have 

 significant ecological implications, 

 and that even within a species (e.g., 

 herring), size at hatching might be an 

 adaptive response to local geographic 

 conditions." 



Walleye pollock Theragra chalco- 

 gramma is a semidemersal species 

 ranging from Japan around the North 

 Pacific rim to central California. This 

 species supports important commer- 

 cial fisheries in the Bering Sea and 

 the Gulf of Alaska. Walleye pollock 

 spawn pelagic eggs which have an in- 

 cubation time of approximately 15 

 days in 5°C water. Egg diameters 

 have been reported to range from 1.0 

 to 1.9 mm (Table 1). Larvae are 3-4 

 mm standard length (SL) at hatching 

 (Dunn and Matarese 1987). Egg size 

 in walleye pollock varies across its 

 geographic range (Table 1). It also 

 varies within populations (Gorbunova 

 1954, Yusa 1954, Nishiyama and Ha- 

 ryu 1981, Sakurai 1982), and over the 

 course of the spawning season (Sero- 

 baba 1968). The causes and signifi- 

 cance of egg size variation in walleye 

 pollock are not well known. 



This field and laboratory study as- 

 sesses sources of variation in walleye 

 pollock egg size and presents results 

 of a preliminary study of the relation- 



471 



