Hinckley Egg size variation of Theragra chalcogramma 



479 



Figure 6A 



Relationship between mean diameter of a batch of walleye 

 pollock eggs spawned in the laboratory, and the mean dry 

 weight of larvae at yolksac absorption. 



Figure 6B 



Relationship between mean dry weight of a batch of 

 walleye pollock eggs spawned in the laboratory, and the 

 mean dry weight of larvae at yolksac absorption. 



relationships in their studies. On the other hand, there 

 are numerous studies in which egg size-female size rela- 

 tionships have been seen, such as Blaxter and Hempel 

 (1963, Clupea harengus), Hislop et al. (1978, Melano- 

 grammus aeglefinus), Grauman (1964, Gadus morhua), 

 Kjesbu (1988, G. morhua), and many on salmonids. 

 Some studies on the same species contradict one 

 another with regards to this relationship. For those 

 species showing a seasonal decline in egg size, an egg 

 size-female size relationship may have been obscured 

 in studies where this was not taken into account. 



Within- and among-population 

 variation in egg size 



The population of walleye pollock spawning in Shelikof 

 Strait shows significant seasonal and annual differ- 

 ences in egg size. The seasonal decline in egg size prob- 



ably covaries with the decline over the spawning cycle. 

 Annual differences in egg size during the peak spawn- 

 ing month (April) in Shelikof Strait appear to be sig- 

 nificant. These yearly differences are apparently not 

 attributable to changes in the size or age composition 

 of the spawning stock, as no relationship between these 

 factors and egg size is apparent. 



It is possible that differences in the date of peak 

 spawning in different years could change the mean egg 

 size in the first week of April (when eggs measured for 

 this study were collected). There is evidence that the 

 mean date of peak spawning was later in 1986 and 1987 

 than in some earlier years (Yoklavich and Bailey 1990). 

 The apparent difference in mean April egg size seen 

 in this study could therefore be a reflection of the 

 variability in time between peak spawning and egg col- 

 lection and the decline in egg size over the spawning 

 season, rather than a true interannual difference. 



