An easy meal: Predicting the effects of prey patch characteristics on humpback whale foraging efficiency on wild and anthropogenic prey sources.
The humpback whale population in Southeast Alaska is growing 6-7% per year. An increasing ecosystem role for these generalist predators is already causing conflicts with fisheries. Within the last few years, salmon hatcheries have reported humpback whales feeding on juvenile salmon at release sites. In Alaska, hatcheries are private non-profit organizations that support sustainable fisheries by supplementing wild fish with fish reared to early life stages in captivity. To mitigate humpback whale predation, hatcheries have been experimenting with different release strategies (timing, fish size, rate of release) that alter the characteristics such as quantity, density, persistence, and individual fish size of the prey field. How these changes alter the foraging efficiency of a humpback whale is unknown. We propose building a model that will predict the energetic costs and expected return of a whale foraging on a particular patch of prey based on characteristics of that prey patch such as species, density, and depth. This model will be informed by morphometric measurements of humpback whales, foraging energetics from dive profiles obtained by tagging with dataloggers and prey surveys with traditional multi-frequency ecosounders and high frequency imaging sonar. We will apply this model to compare the energetic efficiency of a humpback whale feeding on hatchery releases vs. wild prey resources and on various types of hatchery releases. By selecting a release strategy that optimizes early marine survival, hatcheries will increase the catch for commercial, sport and subsistence fishers and processors. This model will be an important tool for understanding how increased foraging from a recovering population of humpback whales impacts Alaska’s marine ecosystems.