154" 



-r 



ALASKA 



Figure 1. — Characteristics of the eastern Bering Sea: A) bathymetry (from Shanna 1979); B) water masses 

 and circulation (from Takenouti and Ohtani 1974); C) surface sediments (from Shanna 1979). 



Water masses in the eastern Bering Sea appear to result from 

 mixing of shelf and oceanic waters within apparently broad zones 

 of interaction along and over the eastern continental shelf. The 

 present concept of dominant long-term mean water circulation is 

 an extremely slow (—1 cm/s) drift to the northwest approximately 

 parallel to the bathymetry (Coachman 1979 3 ). 



Surface sediments of the eastern continental shelf are primarily 

 sand or silt, although gravel and clay components may be present 

 in some local areas (Shanna 1979). 



METHODS 



Survey Approach and Rationale 



For the baseline survey of 1975, the study area was divided into 

 four major statistical subareas, with two subareas (3N,S and 



'Coachman, L. K. 1979. Water circulation and mixing in the southeast 

 Bering Sea. In C. P. McRoy and J. J. Goering (editors), Progress report, 

 PROBES phase I, 1977-78, p. 1-46. Institute of Marine Science, University of 

 Alaska, Fairbanks, AK 99701. 



4N,S) further subdivided into southern and northern regions (Fig. 

 2; Pereyra et al. see footnote 2). Trawling stations were arranged 

 in a systematic grid pattern within each subarea. Subdivisions of 

 the survey area and the density of stations within each subarea 

 were based upon 1 ) the location of potential oil lease sites, 2) prior 

 knowledge of the distribution patterns of principal demersal fish 

 and shellfish species in the study area, and 3) hypotheses that 

 some species may have separate genetically variant southern and 

 northern spawning populations. Sampling density was greatest 

 (one station per 647 km 2 (250 mi 2 )) in subareas 1, 2, and 3N and S 

 where petroleum development activities may take place and where 

 major concentrations of walleye pollock, Theragra chalcogram- 

 ma; yellowfin sole, Limanda aspera; king crab, Paralithodes spp.; 

 Tanner crab, Chionoecetes spp.; and other species are located. 

 These subareas also contain spawning and nursery areas for many 

 of the commercially important species. In subarea 4N and S, 

 where the abundance of adult fish is lower than in subareas 1, 2, 

 and 3N and S, but which is a nursery area for a number of 

 species, sampling density was reduced to one station per 1,036 

 km 2 (400 mi 2 ). 



