Too big to ignore: Foraging strategies and competition between marine top predators in a rapidly changing Bering Sea
Investigators
University of Alaska Anchorage
University of Alaska Fairbanks
Aleut Community of St. Paul Island
Overview
The issue
Our proposed project aligns with Alaska Sea Grant mission, vision, and values by bringing together diverse voices to address coastal resource management needs and inform management of natural resources and fisheries. In 2019, the Bering Sea experienced historically low sea-ice coverage, resulting in a cascade of impacts including a reduction in the cold-pool extent, shifts in the distributions of commercially important fish into the northern Bering Sea, and disruption of subsistence harvests for many coastal Alaskan communities. As the largest pinniped, male Steller sea lions have considerable potential to have significant impacts on marine food webs; however, despite clearly having a demonstrated presence in both the southern and northern Bering Sea regions, there is a significant data gap with little to no information on their ecological role in this ecosystem. For these and other large marine mammal predators, quantifying the top-down and interactive connections relies on diet, biological interactions, and movement data, which can be logistically challenging to collect under normal conditions, let alone a rapidly changing environment. By integrating samples collected through Alaska Native co-management and from commercial fishing fleets, this project will provide critical information on predator-prey interactions, foraging strategies, risk, and competition before, during, and after periods of oceanographic and ecological shifts. Results will also identify directions for future explorations into bycatch reduction and resilience, in the context of climate change. We expect the outcomes of our project will fill a critical knowledge gap, benefit our Tribal partners and the Alaska Native communities throughout the Bering Sea that rely on marine mammals as traditional resources, and inform community and agency stakeholders that are increasingly seeking to use holistic ecosystem-based approaches to management.
Objectives
This proposed project is a partnership between the University of Alaska and the Aleut Community of St. Paul Island (ACSPI) and aligns with the Alaska Sea Grant’s “Healthy Coastal Ecosystems” focus area, mission, vision and core values. We aim to examine the biotic interactions and responses to climate change for an upper trophic-level predator that is of traditional importance to many coastal communities and has both direct and indirect interactions with fisheries in Alaska. To do this, our short-term objectives are to (1) Assess the potential for interspecific competition between sympatric male Steller sea lions (Eumetopias jubatus) and northern fur seals (Callorhinus ursinus) in the Eastern Bering Sea, (2) Characterize the individual variation in foraging strategies for male Steller sea lions in the northern and eastern Bering Sea, within the context of rapid environmental change and risk of direct interactions with fisheries, and (3) Develop compound-specific stable isotope analysis of amino acids as a tool to characterize the inter-annual changes in trophic-position and habitat use of male Steller sea lions foraging in the northern Bering Sea. Together these will advance our long-term strategic capacity for developing robust food-web and bioenergetic models that are critical for informing human-coupled ecosystem-based management of natural resources and fisheries. As both pinniped species are important traditional resources for coastal Alaska Native communities and are co-managed between Tribal and US governments, this project will also advance long-term, sustainable, and inclusive collaborations with diverse partners that address coastal resource management needs, especially for vulnerable communities.
How will researchers conduct their study?
We propose to analyze the bulk carbon and nitrogen stable isotope ratios in male Steller sea lion and northern fur seal tissues, and male Steller sea lion whiskers. These ratios can provide insights into trophic relationships in marine food webs and complex questions of diet and feeding behavior for a range of wildlife. ACSPI manages a robust collection of biosamples from subsistence harvested pinnipeds, as part of their co-management activities with NOAA; and additional Steller sea lion samples will be used from animals bycaught in commercial fisheries in the eastern and northern Bering Sea from 2012-present. Samples will be initially processed in the newly established Bering Sea Research Center on St. Paul Island. This space will enable the graduate student and university researchers a greater connection to the people and place that the samples came from, and will create opportunities for project partners and community members to share their diverse experiences, knowledge, and world views, and build a new collective understanding of the findings. By examining the isotopic niches within and between species, we will gain quantitative insights into contemporary niche partitioning and/or competition occurring in the Bering Sea ecosystem (Objective 1). As whiskers provide a retrospective isotopic timeseries of foraging, we will identify the presence of any isotopic changepoints corresponding temporally with recent marine heatwaves (Objective 2). We will also quantify individual specialization indices, such as the trophic niche width, that can be compared between bycaught and subsistence harvested individuals to asses for factors associated with risk of fisheries interactions (Objective 2). Finally, we will quantify the compound-specific stable isotope analyses of amino acids values in whisker segments to assess this approach as a tool for inferring intra- and interannual movements (Objective 3).
