Muter and Norcross: Distribution, abundance, and growth of Theragra chalcogramma 



585 



20 



Increment count 



Figure 5 



Linear regression of standard length on increment 

 count for otoliths from larval walleye pollock, 

 Theragra chalcogramma, at stations RES 2 and RES 

 4 in Resurrection Bay, Alaska. 



A comparison of elevations (y-intercept) of the two 

 regression lines (Zar, 1984) also resulted in no sig- 

 nificant difference (r=l. 797; 0.05<P<0. 10). Since the 

 two subsamples used for ageing came from different 

 preservatives, no common regression equation was 

 computed. The regression equations relating length 

 and age for larvae preserved in isopropyl alcohol was 



SL = 4.60 mm + 0.18 mm/day x age(days). 



Thus the following equation was used to convert 

 length in isopropyl alcohol to ages: 



Age = (SL-4.60)/0.18. 



Hatch dates 



Estimated hatch dates for all larvae collected 1-4 

 May 1989 ranged from March 29 to May 9 with a 

 median on 22 April (Fig. 7). Without mortality cor- 

 rection the median hatch date was 25 April. 



Figure 7 



Estimated hatch date distributions of larval wall- 

 eye pollock, Theragra chalcogramma, collected in 

 Resurrection Bay, Alaska, 1-4 May 1989. Solid line 

 shows hatch date distribution without mortality cor- 

 rection. "M" indicates median hatch date for mor- 

 tality-corrected distribution. 



