COS 299-3 - Estimating the timing of ringed seal emergence & basking in Arctic Alaska

Abstract: Ringed seals (Pusa hispida) are ice-associated Arctic marine mammals that are a vital resource for Arctic Indigenous peoples, and are ecologically important as the primary prey for polar bears. These seals use snow-covered lairs on sea ice to rest and to protect young pups from hypothermia and predation during winter. As lairs melt and collapse later during spring, the seals emerge onto the surface of the ice to bask and molt. However, the timing of this transition is poorly understood, and this uncertainty hinders interpretation of aerial survey data and our ability to anticipate the potential impact of earlier spring melt on pup survival. Here, we use Hidden Markov Models (HMMs) and haul-out timelines (i.e., in vs. out of the water) from 48 adult ringed seals tagged in the Bering, Chukchi, and Beaufort seas from 2005–2020 to estimate dates of emergence from snow lairs and the onset of basking. We structured our HMMs to include a lair behavioral state and an emerged/basking state, characterized by observed differences in a) the proportion of time a seal spends hauled out per day, and b) peak hour of day at which the seal is hauled out. We also explored covariates on the transition probability between the lair and emerged states including day of year, sea ice concentration, and indices of melt progression. Preliminary results from our models indicate day of year as the strongest predictor of emergence with a mean emergence date of 8 May, which is within one week of previous estimates from aerial surveys. Emergence date was positively associated with latitude, with more northerly seals emerging from lairs later in the spring. Our results provide key information for interpreting aerial survey data, and demonstrate the value of haul-out data from tagged ringed seals for monitoring the timing of emergence in an increasingly dynamic Arctic.