Oceanographic influences on spotted seal foraging in the Pacific Arctic

Abstract

Satellite Relay Data Loggers that are equipped with Conductivity, Temperature, and Depth sensors (CTD-SRDLs) are an important tool for identifying how oceanography influences an animal's foraging behavior and how foraging may be affected by environmental change. Spotted seals (Phoca largha) are one of four species of sea ice-associated seals that occur in the Bering, Chukchi, and Beaufort seas of the Pacific Arctic. Between 2016 and 2020, 23 spotted seals were equipped with CTD-SRDLs, which collected temperature and salinity profiles as the seals dove through the water column. We first examined the oceanographic characteristics along seal tracks using data from the CTD-SRDLs, and then modeled seal behavioral state (resident or transiting) as a function of sea ice and oceanographic conditions extracted from the inferred oceanographic space. We then related these findings to habitat associated with the predominant fish prey species identified from seal stomach contents, which included Arctic cod, saffron cod, Pacific herring, rainbow smelt, and capelin. Spotted seals mostly dove to near-bottom depths, including frequent dives to the sea floor. During the ice-free season in the Chukchi Sea, pups were mostly likely to be in the resident state (i.e., possible foraging) when near-bottom conditions were colder and less saline. Seals were also more likely to be in the resident state when far offshore and in areas with colder bottom temperatures. Behavior related to possible offshore foraging was more associated with non-pup seals and possible nearshore foraging was more associated with pups. During the ice-covered season, seals were more likely to be in the resident state when bottom temperatures were colder, and this relationship was stronger for non-pups than for pups and for females than for males. Our use of satellite telemetry, oceanographic modeling, and biological sampling support the understanding that spotted seals are generalists in both prey species and foraging habitat.