Hinckley Egg size variation of Theragra chalcogramma 



473 



Table 2 



Stratification of walleye pollock egg samples measured for 

 differences in egg size by year, area, and month, and to ex- 

 amine the effect of female size, age, and condition on egg size. 

 Samples were collected on ichthyoplankton cruises in the 

 western Gulf of Alaska. 



Semidi Is. to West of 

 Shelikof Strait Shumagin Is. Shumagin Is. 



Year March April May 



April 



April 



1981 

 1982 

 1984 

 1985 

 1986 



M Y,M M 



M Y,A,M M 



M Y,M M 

 Y 



Samples used to study the effect of year (Y), area (A), month 

 (M), and female (F) age, size, and condition. 



washed with distilled water, placed individually in pre- 

 weighed aluminum boats, dried for 24 hours at 60°C, 

 and weighed on a Cahn 29 electrobalance to the nearest 

 0.001 mg. 



An analysis of variance procedure was used to exam- 

 ine egg size within and among fish. A multiple regres- 

 sion model was used to examine the effect of female 

 length, age, and condition on egg diameter and egg 

 weight. The factors in the regression were fork length, 

 age, body weight (minus ovary weight and liver 

 weight), and liver weight. The model used was 



Y = Bo + 5iA'i + B0X2 + 5,3X3 + B4.Y4 



where Y = egg diameter (mm) or egg dry weight 



(mg), 

 Xi = fork length (cm), 

 Xo = age (yr), 

 Xg = body weight (minus ovary and liver 



weight, g), 

 X4 = liver weight (g). 



Interaction terms were not included in the model 

 until after a test of the overall significance. 



Reference to trade names does not imply endorsement by the Na- 

 tional Marine Fisheries Service, NOAA. 



-60 DON 



166 OOW 164 00 



IS"! 00 



Figure 1 



Western Gulf of Alaska, including Shelikof Strait, a major spawning area for walleye pollock. Shaded areas indicate regions from which samples 

 were taken. 



