Gulf of Alaska | Mammals
Prey species for endangered Cook Inlet beluga whales Presenter: William Bechtol , bechtolresearch@hughes.net, Bechtol Research
Cook Inlet beluga whales (CIBW) are a distinct population segment and an apex predator important for subsistence, culture, and the Cook Inlet ecosystem. During 1993–1998, the CIBW population declined by nearly 50%. Under the Marine Mammal Protection Act, CIBW was listed as depleted in 2000, then listed as endangered under the Endangered Species Act in 2008. During 2008–2018, the CIBW population continued to decline at an average of 2.3% per year, raising concerns on what is inhibiting CIBW recovery. A reduction in the abundance, quality, availability, or seasonality of prey is a threat identified in the CIBW recovery plan. But an understanding of CIBW prey remains uncertain because diet composition has largely been derived from a relatively small number of whales. This analysis updates information on presumed CIBW prey, focusing on anadromous eulachon and salmon which co-occur with CIBW in ice-free months. Spring is a critical time period as CIBW emerge from winter with low energy reserves and must accumulate sufficient energetic reserves to survive the next winter. Adult females are also often lactating or pregnant. Eulachon, a fish with high fat content, aggregate in spring migrations in Upper Cook Inlet, but little quantitative data have been collected on eulachon spawning returns. Agency surveys in adjacent waters, and personal use fisheries, suggest eulachon populations were generally high in the mid-2000s to early 2010s, but are at relatively low levels in recent years. Salmon are presumed to be the major prey during June to August when CIBW build the bulk of their energy reserves. All five species of Pacific salmon occur in Cook Inlet, although salmon availability differs spatially and temporally, and CIBW prey selectively is poorly understood. In the northern inlet where CIBW congregate, commercial salmon harvests are driven by sockeye in the summer and coho in the fall. Commercial salmon harvests, averaged by decade, have declined over the past 40 years. Understanding linkages between CIBW and their prey is critical to adapting management strategies that promote CIBW recovery while maintaining fisheries and ecosystem function. A lack of data on eulachon abundance and CIBW prey selectivity inhibits that understanding. Several potential research options are discussed with the recognition that the listing of “endangered” limits directly interacting with CIBW.
Alaska Marine Science Symposium 2023 245
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