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St. Matthew Island in June 1976 (Fig. 37) may have represented 

 such a migration in progress. 



Catch rates observed during the July and August 1976 sampling 

 of the NMFS Crab-Ground fish Survey indicated that almost all 

 yellowfin sole had migrated from waters west of the Pribilof 

 Islands and most of subarea 2 by midsummer (Fig. 37). 



Because of the sampling problems caused by rapid inshore mi- 

 gration, abundance estimates were imprecise and questionable. 

 Large concentrations of individuals were probably sampled more 

 than once during the April- June 1976 survey period, or even 

 within individual months. Particularly severe biasing due to multi- 

 ple sampling of high fish densities may have occurred during April 

 when sampling was concentrated along the pack ice edge. 



However, because the survey and migrating population ap- 

 peared to progress together, the pattern of sampling may have 

 provided fairly complete coverage of the entire population within 

 each month. As a result, population and biomass estimates were 

 computed overall (April- June), and for comparisons, also for in- 

 dividual months of survey coverage (Table 27). 



The overall apparent population biomass for yellowfin sole was 

 2.09 million t (95% confidence limits 1.17-3.02 million t); the 

 estimated population size was 15.4 billion individuals. Estimates 

 of population biomass obtained from the survey coverage during 

 individual months were April, 5.91 million t; May, 1.31 million t; 

 and June, 1.19 million t (Table 27). 



In relation to previous estimates (Wakabayashi 1975 7 ; Waka- 

 bayashi et al. see footnote 6), the overall and April estimates for 

 yellowfin sole population biomass appear unrealistically high. The 

 May and June estimates were approximately the same as the 

 overall estimate obtained from the 1975 Bering Sea survey (1.04 

 million t; 95% confidence limits 0.87-1.21 million t) and were 

 within the range of the 1975 survey's 95% confidence limits 

 (Pereyra et al. see footnote 2). 



The precision of 1976 survey biomass estimates was relatively 

 poor because of high variability in catch rates between stations 

 and months, and the smaller number of samples upon which each 

 estimate was based. As a measure of relative variance, the width 

 of the 95% confidence limits for each 1976 biomass estimate (ex- 

 pressed as a percentage of the estimated total biomass) was 

 overall, ±44%; April, ±163%; May, ±69%; and June, ±44%. 

 In comparison, the overall relative variance observed in the 1975 

 survey estimate for yellowfin sole was ± 16%. 



During April, May, and June, approximately 79% (range 

 75-86%) of the apparent population biomass was distributed in 

 survey subarea 1 . 



Size composition. — Yellowfin sole taken during the 1976 spring 

 trawl survey ranged from 5 to 44 cm TL, with an overall mean 

 total length of 22.5 cm (based upon 39,352 field measurements, 

 Fig. 38). 



In general, the size-frequency distributions were remarkably 

 symmetrical and similar among all geographical regions of the 

 survey area. Populations in inner shelf subareas 1, 4S, and 4N 

 showed the broadest size range, with higher proportions of small, 

 young individuals ( < 10 cm). Mean total length and the size range 

 in each area were subarea 4N, 19.1 cm (8-41 cm); subarea 4S, 21.3 



'Wakabayashi, K. 1975. Studies on resources of the yellowfin sole in the 

 eastern Bering Sea. II. Stock size estimated by the method of virtual population 

 analysis and its annual changes. Fishery Agency of Japan. Far Seas Fisheries 

 Research Laboratory, 1000 Orido, Shimizu 424, Japan, 22 p. 



53 



