Last updated: June 29, 2021
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Seals Depend on Ice from Tidewater Glaciers
Tidewater glaciers are a defining feature of the southeast Alaska landscape. The ice that calves from the glaciers is important habitat, especially for harbor seals. Seals use the ice to haul out to give birth, rest, protect pups, and to molt.
As tidewater glaciers retreat, we want to know how the changes in ice habitat may impact seals. Understanding how ice habitat changes is important for understanding patterns in the distribution and abundance of harbor seals and the predicted changes to tidewater glaciers and fjord ecosystems. The methods and tools that we have developed over the last several years in Johns Hopkins Inlet will facilitate long-term monitoring of seals and ice habitat in Glacier Bay and along the outer coast in collaboration with National Oceanic and Atmospheric Administration (NOAA)-Marine Mammal Laboratory. This publication is part of a multi-year effort that has focused on developing methods and analytical tools for monitoring the spatial distribution and abundance of harbor seals and floating glacier ice habitat in Johns Hopkins Inlet.
Harbor Seals as Sentinels of Ice Dynamics in Tidewater Glacier Fjords
Abstract
Tidewater glaciers calve icebergs into the marine environment which serve as pupping, molting, and resting habitat for some of the largest seasonal aggregations of harbor seals (Phoca vitulina richardii) in the world. Although they are naturally dynamic, advancing and retreating in response to local climatic and fjord conditions, most tidewater glaciers around the world are thinning and retreating. Climate change models predict continued loss of land-based ice with unknown impacts to organisms such as harbor seals that rely on glacier ice as habitat for critical life history events. To understand the impacts of changing ice availability on harbor seals, we quantified seasonal and annual changes in ice habitat in Johns Hopkins Inlet, a tidewater glacier fjord in Glacier Bay National Park in southeastern Alaska. We conducted systematic aerial photographic surveys (n = 55) of seals and ice during the pupping (June; n = 30) and molting (August; n = 25) periods from 2007 to 2014. Object-based image analysis was used to quantify the availability and spatial distribution of floating ice in the fjord. Multivariate spatial models were developed for jointly modeling stage-structured seal location data and ice habitat. Across all years, there was consistently more ice in the fjord during the pupping season in June than during the molting season in August, which was likely driven by seasonal variation in physical processes that influence the calving dynamics of tidewater glaciers. Non-pup harbor seals and ice were correlated during the pupping season, but this correlation was reduced during the molting season suggesting that harbor seals may respond to changes in habitat differently depending upon trade-offs associated with life history events, such as pupping and molting, and energetic costs and constraints associated with the events.
Womble, J. N., P. J. Williams, R. W. McNabb, A. Prakash, R. Gens, B. S. Sedinger, and C. R. Acevedo. 2021. Harbor seals as sentinels of ice dynamics in tidewater glacier fjords. Frontiers in Marine Science.