2 



slope 



SEXES COMBINED 

 Outer shelf and slope 







25 





c 



® it; 



L. 





a! 10 



A Mean length=33.1 



5 



/ \ n=1643 







J V. 



10 23304O5OG0 7OB0901O0 



3D 



as 



c 



Otf 



Mean length=60.2 

 n=451 



^^^^W- 



0102030405060 70 9390100 



Overall 







25 





C 



S u 





0) ID 



Mean length=33.0 



Q. 

 S 



r\ n-2163 



J v_ 









0102030*5050 70 9050100 



Fork length (cm) 



Figure 75.— Size composition of Pacific halibut taken during the 

 1976 Bering Sea spring trawl survey (see Fig. 3). 



Because longhead dab was not observed to be abundant on the 

 outer shelf at any time during the 1976 spring survey, the popula- 

 tion apparently overwintered on the inner shelf. 



Size composition. — Longhead dab taken during the 1976 spring 

 survey ranged from 10 to 41 cm TL, with an overall mean total 

 length of 23.1 cm (based upon 3,409 field measurements; Fig. 

 77). The observed size-frequency distributions were similar among 

 all geographical regions, sharply unimodal and generally sym- 

 metrical. Largest individuals were observed in subarea 1 (size 

 range 14-41 cm), smallest in subarea 4S (range 10-34 cm). The 

 mean total length of male populations was approximately 78% 

 (range 76-85%) those of the female populations. 



Sex ratio. — The observed proportions of longhead dab females 

 were subarea 1, 0.64; subarea 2, 0.33; subarea 4N, 0.70; subarea 

 4S, 0.63; and overall, 0.64. 



Other species. 



Pacific herring. — Pacific herring, Clupea harengus pallasi, was 

 widely distributed throughout the study area, occurring at 180 

 (41 .4%) of the 435 grid stations at an overall mean abundance of 

 2.01 kg/km trawled (Fig. 78). Highest densities (on a weight basis) 

 were observed along pack ice northwest of St. Paul Island, and 

 northwest and west of Port Moller, but none was taken in deep 

 water on the continental slope. 



The total apparent population biomass within the study area 

 was 35,100 t (Table 63), although this value must have consider- 

 ably underestimated true abundance. Sources of bias may have 

 included 1) low vulnerability to bottom trawling, as a result of a 

 predominantly off-bottom (pelagic) distribution; 2) losses through 

 the trawl mesh; and 3) relatively rapid changes in geographical 

 distribution. 



The distribution of apparent biomass was 48.1% in subareas 3N 

 and 3S, 28.1% in subarea 1, 22.9% in subareas 4S and 4N (com- 

 bined), and only 1.0% in subarea 2. The overall size range taken 

 during the 1976 survey was 20-31 cm FL. 



Table 62. 



-Estimated biomass and population numbers of longhead dab by subarea and for all subareas combined, 1976 

 Bering Sea spring trawl survey. 











Proportion 





Proportion 









Percentage 

 frequency of 



Mean 

 CPUE 



Estimated 

 biomass 



of total 

 estimated 



Estimated 

 population 



of total 

 estimated 



Mean 



size 





Weight 



TL 



Subarea' 



occurrence 



(kg/km) 



(t) 



biomass 



(millions) 



population 



(kg) 



(cm) 



Inner shelf 



















4N 



40.9 



1.34 



2,481 



0.076 



17.5 



0.061 



0.142 



22.6 



4S 



58.9 



1.38 



5,945 



0.181 



58.1 



0.203 



0.102 



22.6 



1 



72.0 



4.93 



24,158 



0.737 



209.4 



0.731 



0.115 



23.3 



Outer shelf 



















and slope 

 3 

 3 Slope 























— 



— 



_ 



_ 











— 



2 



4.5 



0.05 



184 



0.006 



1.3 



0.005 



0.145 



21.1 



2 Slope 



- 



- 



- 



- 



- 



- 



- 



- 



All subareas 



















combined 



27.1 



1.62 



'32,767 





286.2 





0.114 



23.1 



'See Figure 3. 



! 95<Fo confidence limits: 21.793-43,714 t. 



106 



