Table 63. — Estimates of the biomass of other fish populations, 1976 Bering Sea spring trawl survey. 





Inner 



sheif subareas' 



Outer shelf and slope subareas 1 



All sub 





Species 



I 



4S 



4N 



2 



2 Slope 



3 



3 Slope 



areas combined 2 





















Pacific herring 



9,872 



3,975 



4,064 



338 





16,882 







35,131 



(12,058-58,204) 



Starry flounder 



5,891 



529 



95 



2,698 



— 



55 



— 



9,268 



(4,607-13,933) 



Pacific ocean perch 



— 



— 



— 



33 



784 



48 



549 



1,414 



(185- 2,643) 



Saffron cod 



10 



5 



— 



949 



— 



6 



— 



970 



(0- 2,389) 



Bering flounder 



— 



25 



356 



— 



— 



547 



— 



928 



(157- 1,701) 



Sablefish 



- 



— 



— 



215 



338 



- 



28 



581 



(14- 1,148) 



'See Figure 3. 



Parentheses enclose 95% confidence limits for the overall estimates. 



Starry flounder. — Starry flounder, Platichthys stellatus, was 

 taken at 97 (22.3%) of the 435 grid stations at an overall mean 

 abundance of 1.20 kg/km trawled. Although occurring at scat- 

 tered locations over most of the continental shelf, highest densities 

 were observed along the Alaska Peninsula. The total apparent 

 population biomass within the study area was 9,300 t (Table 63), 

 with 15.3 million individuals. The observed distribution of ap- 

 parent biomass was 63.6% in subarea 1, 29.1% in subarea 2, and 

 7.3% in subareas 3N, 3S, 4S, and 4N (combined). Starry flounder 

 was not taken in deep water along the continental slope. 



Pacific ocean perch. — Pacific ocean perch, Sebastes alutus, 

 was taken at 30 (6.9%) of the 435 grid stations, at an overall mean 

 abundance of 0.07 kg/km trawled. Pacific ocean perch occurred 

 only in deep water along the outer edge of the continental shelf 

 and slope. The total apparent population biomass within the 

 study area was 1,400 1 (Table 63), with 1.5 million individuals. The 

 distribution of apparent biomass was 55.4% in subarea 2 Slope, 

 38.8% in subarea 3 Slope, and 5.7% in subareas 2 and 3 (combined). 



Saffron cod. — Saffron cod, Eleginus gracilis, was recorded at 

 only 9 (2. 1 %) of the 435 grid stations, at an overall mean abun- 

 dance of 0.05 kg/km trawled. Occurrences were scattered over 

 central and inner regions of the continental shelf. The total ap- 

 parent population biomass within the study area was 970 t (Table 

 63), a value of only 5.1% of the 1975 survey estimate of 19,100 t 

 (Pereyra et al. see footnote 2). Although this large difference may 

 have been caused by a change in vulnerability to bottom trawling, 

 it was more likely a result of misidentifications and confusion of 

 specimens with Pacific cod. 



Bering flounder. —Bering flounder, Hippoglossoides robustus, 

 was recorded along the outer continental shelf in the extreme 

 northern region of the study area, occurring at 26 (6.0%) of the 

 435 grid stations, at an overall mean abundance of 0.04 kg/km 

 trawled. The total apparent population biomass within the study 

 area was 930 t (Table 63), with 2.9 million individuals. 



The distribution of apparent biomass was 58.9% in subareas 

 3N and 3S, 38.4% in subarea 4N, and 2.7% in subarea 4S. 

 Specimens identified as Bering flounder ranged from 14 to 41 cm 

 TL. The observed ranges in age were males, 5-15 yr, and females, 

 5-24 yr. 



Sablefish. — Sablefish, Anoplopoma fimbria, was taken at 30 

 (6.9%) of the 435 grid stations, at an overall mean abundance of 

 0.03 kg/km trawled. Occurrences were observed only in deep 

 water along the outer continental shelf and slope. The total appar- 



ent population biomass within the study area was 580 1 (Table 63), 

 with 0.4 million individuals. The distribution of apparent biomass 

 was 58.2% in subarea 2 Slope, 37.0% in subarea 2, and 4.8% in 

 subarea 3 Slope. Sablefish ranged from 38 to 62 cm FL. 



DISCUSSION 

 Review of Survey Approach and Findings 



The August-October 1975 and April- June 1976 demersal trawl 

 surveys provided new opportunities for comprehensive assessment 

 of the eastern Bering Sea ichthyofauna. Both surveys were ex- 

 tremely broad in geographical coverage, and consistent sampling 

 methods enabled direct comparability. And importantly, the tem- 

 poral coverage of the two surveys enabled analyses of natural 

 variability at seasonal and year-to-year time scales. 



Although 235 fish species have been reported to occur in the 

 eastern Bering Sea (Shmidt 1950), only 76 and 78 fish taxa were 

 recorded during the 1975 and 1976 surveys. Of these, the most 

 abundant 20 taxa accounted for approximately 98% of the overall 

 total weight (or also, total apparent biomass) of demersal fishes 

 recorded during the two surveys. Of these 20 most abundant 

 demersal taxa, 10 species account for 99% of present commercial 

 fish landings. 



On the expansive eastern Bering Sea soft-bottom continental 

 shelf, the demersal fish community appears to be dominated (on 

 the basis of weight density) by a few species, and these species 

 tend to be distributed somewhat predictably in both space and 

 time. This predictability might be described in the context of a 

 simple migratory circuits model (Fig. 79). Adult populations 

 generally migrate to, and concentrate at, relatively well-defined 

 spawning locations within a relatively specific seasonal time 

 period. Egg and larval drift, and later swimming behavior, take 

 juveniles to nursery areas — usually isolated from the adult 

 population, inshore or in shallower water. As juveniles mature, 

 recruitment to the adult stock occurs as a result of growth, off- 

 shore migration, and changes in behavior. During the seasonal cy- 

 cle, adult stocks migrate between overwintering regions, spawning 

 locations, and feeding areas of presumably high food abundance. 



Freezing avoidance mechanisms are an important adaptation of 

 eastern Bering Sea fishes to their environment. All marine teleosts 

 are hypotonic to seawater, and the blood freezing points of most 

 species are approximately -0.5° to -0.8°C (Somero and 

 Hochachka 1976). Under winter ice cover, bottom water 

 temperatures over most of the eastern Bering Sea continental shelf 

 are near the freezing point of seawater ( - 1 .6 ° to -1.7 °C). Even 



110 



