. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering I60« _J. Figure 37-18. Percent of monthly mean zooplankton standing stock consumed in February and in August in the eastern Ber- ing Sea. birds are apex predators, their effect on the ecosys- tem being similar to the effect of fishing by man. In addition to the fact that the occurrence of mammals is seasonal and their distribution uneven, their mobility has various temporal and spatial dynamic effects on the rest of the ecosystem. Esti- mates of numbers of marine
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering I60« _J. Figure 37-18. Percent of monthly mean zooplankton standing stock consumed in February and in August in the eastern Ber- ing Sea. birds are apex predators, their effect on the ecosys- tem being similar to the effect of fishing by man. In addition to the fact that the occurrence of mammals is seasonal and their distribution uneven, their mobility has various temporal and spatial dynamic effects on the rest of the ecosystem. Esti- mates of numbers of marine mammals present vary considerably from one source to another. It is apparent that some of the estimates have little to do with reality. There are three types of seasonal occurrence of mammals—the winter visitors (, "ice" seal and bowhead whale), summer visitors (, fur seal, sea lion, and sperm whale), and year-round residents (, beluga whale). The estimates of daily food requirements of marine mammals are also variable in the literature. The more conservative estimates are between 4 and 8 percent body weight daily, depending on the species, and these estimates were used in the model. Seasonal changes of some marine mammals and birds are shown in Fig. 37-19; these estimates are believed to be the best and most realistic estimates, found in various more reliable sources in the litera- ture. The consumption of fish by marine mammals and birds in the area is about 3 million mt a year, which is about twice the total area catch by the fishery of aU nations. The effect on the ecosystem of consumption by marine mammals is similar to the effect of the fishery—continual removal of biomass without pro- viding much return in the form of food for other biota in the ecosystem. Considering the magnitude of consumption by mammals in relation to harvest by. Please note that these images are extracted from scanned page images that may have been digitally enhanced for
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