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Fishery Bulletin 100(2) 



gi'eatest number of stations were sampled in the 100-200 

 m bottom-depth category and in the 0-20 nmi distance- 

 from-land category. 



The results were standardized by taking the proportion 

 of stations within each category that had a positive oc- 

 currence of pollock ( Fig. 5 ). These graphs showed that for 

 each bottom depth category, the proportion of positive oc- 

 currences had increased over the years. The proportion 

 of stations where pollock were present was consistently 

 high in the 0-20 nmi category (Fig. 5). Farther from land, 

 the proportion of positive stations increased between 1984 

 and 1996. In all three geogi'aphic regions, there was an 

 increase in the proportion of stations where pollock were 

 present. 



Table 4 lists the number of hauls with pollock occur- 

 rence and summarizes the CPUE values for the nonzero 

 data. Results from the single-factor ANOVAs calculated 

 for the nonzero density data are summarized in Table 5. 

 Significant differences were observed among most years. 



except for the Chirikof region and the distances from land 

 ofO-20 and 40-60 nmi. 



Adult pollock 



The initial three-dimensional contingency tables of mutual 

 independence between adult pollock occurrence and the 

 three physical characteristics proved significant. Subse- 

 quent contingency analyses revealed significant results for 

 all partial independence tests except for the two-dimen- 

 sional test for independence between occurrence of adult 

 pollock and geographic region (P=0.58). 



Examination of all the positive data showed that the 

 mean of the log-transformed CPUE decreased and the 

 variance increased over time for bottom depths 100-200 

 m in each geogi-aphic area (Table 6). The mean CPUE also 

 decreased over time for stations <40 nmi from land but 

 there was no trend in the changes in variance (Table 6). 

 The ANOVA confirmed that changes in the distribution of 

 pollock from 1984 to 1996 were significant (a=0. 05) among 

 years at all depth intei-vals, all geographic areas , and at a 

 distance from land <60 nmi (Table 7). Thus, although the 

 number of stations where pollock could be encountered in- 

 creased (e.g. the low-density distribution data), the mean 

 adult pollock density decreased and became more variable 

 between 1984 and 1996 (Fig. 5, Table 6). 



Changes in the distribution of adult pollock were fur- 

 ther examined by sorting the data into seven CPUE bins 

 and by making histogi'ams of the frequency of stations 

 within each bin (Fig. 6). The histogram revealed that 

 over the years, the occurrence of stations with zero adult 

 pollock CPUE decreased, whereas stations with low-den- 

 sity (CPUE <1000 fish/km-) concentrations of pollock in- 

 creased. Higher density stations did not exhibit any par- 

 ticular trend. 



To better understand observed changes in the distribu- 

 tion of low-density concentrations of adult pollock, all the 

 stations were characterized by bottom depth, geographic 

 location, and distance from land (Fig. 7). The number of 

 stations that had low-density concentrations of adult pol- 

 lock increased in all habitat categories over the years. The 

 proportion of stations within each bottom depth bin with 

 low-density concentrations of adult pollock more than dou- 

 bled from 1990 to 1996. Comparable dramatic increases 

 were obsei-ved with regard to distance from land and geo- 

 graphic region. 



Juvenile pollock 



Contingency table analysis for juvenile pollock occurrence 

 resulted in significant (P<0.001) results across all ages for 

 tests of mutual independence among all the physical char- 

 acteristics. Two-dimensional contingency analyses also 

 resulted in significant results. It was difficult to discern 

 any chronological trends in the mean and variance of all 

 the positive data for juvenile pollock. Minor fluctuations in 

 juvenile pollock density may have been related to interan- 

 nual differences in year-class strength (Table 1). 



Histograms similar to those for adult pollock were made 

 for all three juvenile age groups of pollock, where juvenile 



