. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . ieo° 17S' Figure 33-2. The apparent density distribution of walleye pollock during August-October 1975, determined by a research vessel survey (Pereyra et al. 1976). Figure 33-3. The apparent density distribution of walleye pollock during April-June 1976, determined by a research vessel survey (Bakkala and Smith 1978). highest densities along the shelf edge (Figs. 33-2 and 33-3). The overall distribution pattern varies season- ally and between years, dominated by movements between deep a
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . ieo° 17S' Figure 33-2. The apparent density distribution of walleye pollock during August-October 1975, determined by a research vessel survey (Pereyra et al. 1976). Figure 33-3. The apparent density distribution of walleye pollock during April-June 1976, determined by a research vessel survey (Bakkala and Smith 1978). highest densities along the shelf edge (Figs. 33-2 and 33-3). The overall distribution pattern varies season- ally and between years, dominated by movements between deep and shallow water. Over the contin- ental shelf pollock show a semidemersal behavior, tending to form schools near the bottom during daytime, then dispersing up into the water column at night. Along the outer continental shelf and slope, dense shoals are formed that may exceed 20-50 km in length and have mean densities of up to 9 mt per hectare. Figs. 33-4 and 33-5 show two examples of the apparent depth distribution of pollock on the eastern Bering Sea continental shelf, determined from re- search vessel surveys. During August-October 1975, pollock were relatively symmetrically distributed around a median depth of approximately 200 m. During April-June 1976, the vertical pattern was less symmetrical but similar, although apparent densities were lower among all depth intervals except 400-450 m. The domain within which pollock occur demersally Apparent Density (kg/ha) 50 100 150 200 100 -g 200 a Q 300 400 1 ' ' 1 ' III sflii MEAN POLLOCK ABUNDANCE August-October 1975 500 Figure 33-4. Apparent vertical distribution of pollock densities on the continental shelf during August-October 1975 (based upon the data shown in Fig. 33-2). Apparent Density (kg/ha) 50 100 150 100 E 200 Q. V Q 300 400 500 200 —I MEAN POLLOCK ABUNDANCE Aprif-June 1976 Figure 33-5. Apparent vertical distribution of pollock densities on the continental shelf during April-June 1976 (based on the data shown in Fi
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