Hinckley: Egg size variation of Theragra chalcogramma 



475 



A significant difference in mean egg diameters was 

 also observed over the course of tiie spawning season 

 (March-May) in Sheiikof Strait (Table 4) in 1981 (F = 

 23.389, p<6.0005), 1982 (F= 16.3387, 0.01<jt)<0.025), 

 and 1984 (F= 54.105, /><0.0005*). In 1981 and 1984 

 egg sizes decreased over the course of the spawning 

 season by about 7% per month (Table 4, 0.02 <p< 0.05). 

 In 1982, mean egg diameter apparently increased from 

 April to May by 1.4%. 



Unpreserved walleye pollock eggs collected from the 

 plankton in the Gulf of Alaska (in April 1987) were 

 larger in diameter (x 1.36 mm, range 1.30-1.41) and 

 dry weight (x 0.120 mg, range 0.097-0.139) than 

 fresh eggs from Puget Sound (diameter i 1.19 mm, 

 1.03-1.27; dry weight x 0.077, 0.052-0.092), which 

 were spawned naturally in laboratory tanks in April 

 1987. Mean egg diameters from various parts of the 

 spawning range within the Gulf of Alaska were also 

 compared from collections in April 1982 (Table 5). Egg 

 sizes differed among all of the areas examined {F = 

 18.854, p<0.0005). Egg sizes showed a decrease of 

 7.2% from Sheiikof Strait westward to Unimak Pass. 



Table 6 



Correlation coefficients (r) between walleye pollock egg 

 diameter and egg dry weight, and female length, age. body 

 weight, and liver weight. 



Length Age 



Body Liver 



weight weight 



Egg diameter 

 Egg dry weight 



0.210 

 0.294 



0.245 

 0.297 



0.080 0.171 



0.125 0.070 



< 0.001) than variation within fish. Correlation coeffi- 

 cients between egg diameter or egg dry weight and 

 female length, age, body weight, and liver weight are 

 presented in Table 6. 



The multiple regressions of egg diameter and dry 

 weight against fish length, age, body weight, and liver 

 weight were nonsignificant (R'~ = 0.361, 0.10<;j<0.25, 

 and /?- = 0.321, jo>0.25, respectively). A stepwise 

 regression eliminated all variables as nonsignificant 

 (;.)>0.05). No interactions or nonlinear relationships 

 among variables were found. Fourteen females (29.5- 

 47.0 cm PL) were held in the laboratory to investigate 

 the female length-egg size relationship. As in previous 

 regression analyses, no relationship was seen between 

 female length and egg diameter for these fish (Fig. 2, 

 r = 0.006). 



Relationship between 



egg size and female characteristics 



The mean diameter of hydrated eggs taken from Sheii- 

 kof Strait females in 1986 was 1.41 mm (range 1.29- 

 1.57). The mean dry weight of these eggs was 0.119 

 mg (range 0.095-0.148). Variation in egg diameter and 

 egg dry weight among fish was more significant (/j 



*Satterthwaite approximation not used in this test as the criteria 

 were not met. A simple approximation test (Sokal and Rohlf 1981) 

 was used in this case. 



Spawning characteristics and the 

 relationship of egg size to larval size 



The number of egg batches spawned per female in the 

 laboratory in 1987 ranged from 2 to 21 over 3-26 days 

 (Table 7). Excluding the two females which died pre- 

 maturely, the average number of batches was 14.4 

 (range 9-21), and the average duration of spawning 

 was 21.4 days (range 18-26). The average interval be- 

 tween batches for all fish was 2.1 days (range 1-5). The 

 relationship between egg diameter and egg dry weight 

 was linear (7.><0.0005, R'~ = 0.630). 



