Factors Affecting the Diets of Groundfish in the Gulf of Alaska

Modeling ecosystem dynamics and implementation of ecosystem management has become a research priority in marine fisheries. A wide variety of approaches have been taken to model fisheries in a multispecies framework.  However, most previous efforts in modeling inter-species interactions have been somewhat restricted in the functional form of predators’ foraging responses. Most commonly, a predator’s functional response is assumed to depend on prey density alone (e.g., the Holling functional responses). However, ecological evidence suggests that predators may also respond to other factors, such as habitat and temperature. These abiotic factors have been shown to alter behavior and activity of predators and prey. Furthermore, non-additive predation effects, in which one predator facilitates another by altering prey behavior has been illustrated in a variety of aquatic systems. The Gulf of Alaska (GOA) ecosystem is highly diverse and sustains multiple large marine fisheries. I used a time series of data on the diets of three groundfish predators, Pacific cod, Pacific Halibut and sablefish in this system as a case study. Several abiotic and biotic environmental factors were investigated that could affect diet and predatory dynamics. Diet metrics are related to temperature, habitat type, location, and the density of competitors and other predators by using multivariate and linear regression statistical approaches. Results suggest that in some regions of the gulf, the overall make up of diets of these predators changes in regards to these environmental factors. More specifically, the amount and length distribution of walleye pollock consumed varies as a function of these factors in some subsets of these data. Results are dependent on the level of spatial aggregation used in the analysis with results differing across predators when stomachs were described at the regional level versus that of the entire GOA.