Quantify Foraging Success of Northern Fur Seals in Relation to Fine-scale Prey Availability: Preliminary Findings from Saildrones and Seal-borne Sensors

Carey Kuhn1, Jeremy Sterling1, Alex De Robertis2, Mike Levine3, Burlyn Birkemeier4, Molly McCormley5, Calvin W. Mordy6, Heather M. Tabisola7 and Christian Meinig8, (1)NOAA Alaska Fisheries Science Center, Marine Mammal Laboratory, Seattle, WA, United States, (2)NOAA Fisheries, Alaska Fisheries Science Center, Midwater Assessment and Conservation Engineering, Seattle, WA, United States, (3)NOAA Fisheries, Alaska Fisheries Science Center, Seattl, WA, United States, (4)Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA, United States, (5)Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, United States, (6)Joint Institute for the Study of the Atmosphere and Ocean, Seattle, WA, United States, (7)University of Washington, Cooperative Institute for Climate, Ocean, and Ecosystem Studies / NOAA PMEL, Seattle, United States, (8)NOAA Pacific Marine Environmental Laboratory, Seattle, WA, United States
Abstract:
To model or predict the impact of changes in prey resources, it is necessary to understand relationships between prey availability and predator foraging success. However, for many marine predators, data on the distribution and abundance of prey throughout the foraging range are not available, let alone fine-scale measurements near a foraging individual. In addition, quantifying foraging success is challenging due to the inability to make direct observations of feeding events. Here, we present preliminary data from a study that integrated large-scale prey mapping with concurrent measures of northern fur seal (Callorhinus ursinus) behavior to examine foraging success in relation to prey availability. In 2017 and 2019, a Saildrone unmanned surface vehicle equipped with a fisheries echosounder mapped the abundance and depth distribution of the fur seals primary prey, walleye pollock (Gadus chalcogrammus). The at-sea behavior of fur seals from St. Paul Island (Alaska) was measured using satellite-linked dive recorders and prey consumption events were recorded using animal-borne video cameras. Acoustic backscatter was classified into two categories: aggregations of age-0 pollock and adult pollock based on observed aggregation characteristics and depth distributions. Two independent reviewers classified prey capture attempts, capture success, and prey size for each recorded video. For three fur seals, capture rates (per dive and hour of diving) were examined in relation to multiple measures of prey availability, such as backscatter by age-class and depth distribution. This study demonstrates the success of using unmanned surface vehicles to collect prey data over large areas to examine factors that influence predator foraging success. These data can be used to fill significant gaps in our understanding of how northern fur seals respond to variation in prey resources, which is essential to develop ecosystem-based approaches for northern fur seal conservation and fisheries management.
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