. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . :â¢- -^-: ."-c?*- -S'leo^-*^' 170- Sâs 22-45 cm Auguit 160' _j Figure 37-8. Sources and sinks of maturing pollock (22-45 cm long) in February and in August in the eastern Bering Sea (in lOOkg/km^). cm, and maturing pollock, 22 to 45 cm). Source refers to the area where biomass growth in a given time interval (month) exceeds its losses by predation, fishery, and other causes of mortality; sink refers to the opposite condition, , losses exceed growth. The sources and sinks of olde
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . :â¢- -^-: ."-c?*- -S'leo^-*^' 170- Sâs 22-45 cm Auguit 160' _j Figure 37-8. Sources and sinks of maturing pollock (22-45 cm long) in February and in August in the eastern Bering Sea (in lOOkg/km^). cm, and maturing pollock, 22 to 45 cm). Source refers to the area where biomass growth in a given time interval (month) exceeds its losses by predation, fishery, and other causes of mortality; sink refers to the opposite condition, , losses exceed growth. The sources and sinks of older pollock (>45 cm) are not shown because this size group has only sinks (large senescence and spawning mortality, fishery, and small growth rate) which are roughly proportion- al to biomass present. The sources and sinks of all species change because of spatial and temporal changes of the processes which cause them. There is usually a sink at the periphery of the distribution of the biomass. This sink is usually compensated for by outmigration from the center of main distribution (spreading). There is a nearly continuous source of pollock off the conti- nental slope over the deep water; during winter this source area is displaced southwest where the tempera- ture of the water is higher, allowing higher growth rates. The distribution of the three different age groups of pollock in August is shown in Figs. 37-9, 37-10, and 37-11. A partial separation of juvenile and old pollock is brought about by cannibalistic predation of older pollock on its own juveniles. The highest concentration of biomass of older pollock is found off the continental slope, whereas the juveniles are found mainly on the continental shelf. The effects of seasonal depth-migrations of yellow- fin sole on its distribution changes are shown in Figs. 37-12, 37-13, and 37-14. The seasonal depth migra- tions of flatfish were investigated by Alverson (1960) and on the basis of his work it was assumed that yell
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