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Many multispecies models have assumed that prey density determines the per-capita predator consumption rates, following a functional response relationship. However, empirical evidence suggests that a predator’s diet can also be influenced by a variety of environmental factors, including interactions with other predators. Researchers in this study used diet and abundance data from the National Marine Fisheries Service (NMFS) bottom trawl surveys for three groundfish predators Pacific cod, Pacific halibut, and sablefish in the Gulf of Alaska to determine whether temperature or other species influence the consumption of walleye pollock.
Using an information-theoretic approach, researchers tested for relationships between walleye Pollock observed in predator stomachs and predator length, bottom temperature, prey availability (walleye Pollock catch per unit effort (CPUE) scaled by observed prey lengths), and CPUE of the three predators and arrowtooth flounder. Predator length was positively related to walleye Pollock presence and proportion of total diet mass in all predators. Increased temperatures negatively affected consumption of walleye Pollock by Pacific halibut, but not the other predators. Researchers found evidence for a number of inter-predator effects of co-occurring predators, both positive (facultative) and negative (competitive). Surprisingly, observed prey density was not statistically significant with respect to consumption for these predators, suggesting that trawls sample the environment far differently than walleye Pollock predators or species interactions are more complex than those used in previous multispecies models. These factors should be considered for future models contributing to ecosystem-based management.
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