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



583 



Q- 



Q 



100 



150 



200 



150 



RES 1 



RES 2 



RES 25 



RES 3 



RES 4 , 



GAK 1 



8 12 



Abundance (number/m 3 ) 



Figure 4 



Vertical distribution of walleye pollock larvae, Theragra chalcogramma, in Res- 

 urrection Bay, Alaska, 7-9 June 1989. 



the largest number of larvae was captured at RES 3 

 at 58 m. Abundance averaged across all stations de- 

 creased from 281 larvaem -2 in early May 1989 to 

 4.6 larvae-m -2 five weeks later. 



Larval size distribution 



Mean SL of larvae differed significantly with depth 

 at all stations in early May (Table 2). Both a t-test 

 and a Mann-Whitney test of differences between 

 means showed highly significant differences between 



the shallow and deep samples at RES 1, 2, 2.5, 3, 

 and RES 4 (P<0.01). An ANOVA for station GAK 1 

 suggested highly significant differences as well 

 (F=42.33; P<0.001). Results from a Tukey HSD test 

 showed significant differences in mean standard 

 length between the samples from 22 m and 65 m at 

 GAK 1 (P=0.01). Differences between any of the re- 

 maining pairs at GAK 1 were not significant. 



While significant differences in size with depth 

 existed at all stations, the sign of the differences 

 varied between stations. At the two innermost sta- 

 tions (RES 1 and RES 2) larval size decreased with 

 depth, whereas at all other stations the opposite 

 trend was found, i.e. larval size increased with depth, 

 excluding the sample from 100 m at GAK 1. This 

 sample showed a slight decrease in mean SL com- 

 pared to shallower samples, but the difference was 

 not significant. 



To compare larval size between stations, mean SL 

 was corrected for sample date by using observed 

 growth rates. Since we sampled over a four-day pe- 

 riod, the measured lengths differed because of growth 

 during this period. Thus, standard length was cor- 

 rected for date of sampling by using a growth rate of 

 0.18 mm/day, the overall growth rate of pollock lar- 

 vae in Resurrection Bay (this study). Table 2 shows 



