Hinckley Egg size variation of Theragra chalcogramma 



477 



Figure 4A 



Relationship between mean diameter of a batch of walleye 

 pollock eggs spawned in the laboratory, and the mean stan- 

 dard length of larvae hatched from that batch. 



Figure 4B 



Relationship between mean dry weight of a batch of 

 walleye pollock eggs spawned in the laboratory, and the 

 mean standard length of larvae hatched from that batch. 



Mean egg diameter per batch of eggs spawned de- 

 clined over the spawning cycle of an individual for all 

 females (Fig. 3). The average decline in egg diameter 

 over the batch spawning cycle (for females that com- 

 pleted spawning) was 0.14 mm, or 11,5% of the initial 

 egg diameter. 



Thirty-three batches of eggs were incubated and 

 hatched. Larval standard length at hatch was positively 

 correlated with egg diameter (Fig. 4A) and egg dry 

 weight (Fig, 4B). The regressions of larval length at 

 hatch on egg diameter and dry weight were both sig- 

 nificant (0.001<io<0.0025, i?"- = 0,385, and O.OOK;) 

 <0.0025, i?2 = 0.351, respectively). 



Eighteen batches of larvae were raised to yolk-sac 

 absorption and measured. The relationship between 

 egg size and larval size at yolksac absorption was more 

 variable than at hatch. Both egg diameter and dry 

 weight were significantly correlated with larval length 

 at yolksac absorption (0.025<p<0,05 and 0,005</)< 

 0.01, respectively; Fig. 5 A, B). 



Egg diameter varied positively with larval dry weight 

 at yolksac absorption (Fig, 6A, 0.0025<p<0.005, R- 

 = 0.462), as did egg dry weight and larval dry weight 

 at yolksac absorption (Fig. 6B, p< 0,0005, R- = 0.852), 



Discussion 



Characteristics of spawning 



The laboratory work from this study supports Sakurai's 

 (1982) evidence that the batch spawning process in 

 walleye pollock (which are partially synchronous 

 spawners; Hinckley 1987) extends over a period of 

 about a month, at least in the laboratory. Sakurai's 

 walleye pollock, however, spawned approximately 

 every 3 days, whereas walleye pollock in this study 

 spawned about every 2 days. This probably reflects the 

 effect of higher water temperatures in this study (i 

 10. rC, versus 3.5-7,6°C in Sakurai's study). Higher 

 temperatures have been shown to decrease the inter- 



