A multispecies virtual population analysis of the eastern Bering Sea

The eastern Bering Sea shelf supports a large biomass of several groundfish populations, particularly walleye pollock (Theragra chalcogramma). The main trophic interactions between dominant groundfish populations in this region involve walleye pollock as prey. A multispecies virtual population analysis model (MSVPA) covering the period 1979–1995 has been parameterized for the eastern Bering Sea in order to move closer to providing multispecies management advice for this region. The MSVPA model is based on extensive diet data from 70 predator/prey/year/quarter combinations and currently includes the following species as predators: walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), Greenland turbot (Reinhardtius hippoglossoides), yellowfin sole (Pleuronectes asper), arrowtooth flounder (Atheresthes stomias), and northern fur seal (Callorhinus ursinus). Arrowtooth flounder and northern fur seals are entered as ‘‘other predators’’, which means that population and mortality estimates are not directly made for these species. Estimates of their consumption rates, diet, and population abundance are input, however, so that their predation on prey species in the model can be calculated. Prey species are walleye pollock, Pacific cod, Greenland turbot, yellowfin sole, rock sole (Lepidopsetta bilineatus), and Pacific herring (Clupea pallasi). Results show that large numbers of walleye pollock, particularly age-0 and age-1 fish, are consumed and cannibalism by adult pollock constitutes the largest source of predation mortality for age-0 fish. Predation plays an important role in explaining the recruitment dynamics of pollock. Further advances may be made when these estimates are linked to models that examine the effect of climate-related factors influencing larval survival.