Statewide | Seabirds
Modeling seabird distribution and abundance in Alaska’s marine ecosystems: Synthesis of change Presenter: Brian Hoover , bhoover@faralloninstitute.org, Farallon Institute Kathy Kuletz , kkuletz@gmail.com, US Fish and Wildlife Service
John Piatt , jpiatt@usgs.gov, US Geological Survey Alaska Science Center Maymui Arimitsu , marimitsu@usgs.gov, USGS Alaska Science Center Sarah Ann Thompson , sathompson@faralloninstitute.org, Farallon Institute Marisol Garcia-Reyes , marisolgr@faralloninstitute.org, Farallon Institute Heather Renner , heather_renner@fws.gov, Alaska Maritime National Wildlife Refuge William Sydeman , wsydeman@faralloninstitute.org, Farallon Institute
In Alaska’s marine ecosystems, distributions and long-term population trends of seabirds serve as valuable indicators of ecosystem health and stability. We have initiated a multi-pronged approach towards improving our understanding of how seabirds respond to and reveal climate-linked shifts in Alaska’s oceans. As a first step, we examine the relationship between two methods of tracking seabird abundance trends. Seabird population size is monitored both at sea and via land-based colony counts, with each approach measuring different portions of the population. It remains unclear how closely linked these data sets are in population trends or in their responsiveness to climate change – for example, some age-classes and species remain at sea even during the breeding season, and colony counts may account for only half of a region’s total seabird population. Integrative and comparative approaches are thus needed to understand how climate change is affecting seabird populations both at sea and on land. In particular, new approaches are required that can accommodate the biases found in at-sea data, such as inconsistent survey coverage across space and time, and variability in detection due to weather, observers, and vessel platforms. To address this, we are using at sea survey data from the newly updated North Pacific Pelagic Seabird Database (1974-2021) and applying multi-species Vector Autoregressive Spatio-Temporal (VAST) models to produce population estimates for key seabird species within Alaskan waters. The VAST framework uses a delta-generalized mixed model approach to estimate spatial variation in species density using both encounter probabilities and positive counts and can be extended to simultaneously estimate spatio-temporal variation in density for multiple species. We present preliminary results for one of our project’s objectives, which is to compare annual VAST-derived abundance trends of at-sea seabirds with colony-derived population trends (8 colonies monitored by the Alaska Maritime National Wildlife Refuge, in addition to data from Round Island and Cape Peirce; 1974–2021). Subsequent objectives will examine seasonal fluxes in seabird community structure, and whether shifts in the distribution of seabirds track the “velocity” (rate) of climate change. This novel approach will advance our understanding of how population trends from at-sea and colony surveys are linked, and more broadly inform how seabird populations are affected by climate change.
Alaska Marine Science Symposium 2023 232
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