Use of glacial and terrestrial habitats by harbor seals in Glacier Bay, Alaska: costs and benefits

摘要

Among pinnipeds, harbor seals Phoca vitulina have the broadest distribution (a 34° to 50° range in latitudes in the Pacific and Atlantic regions, respectively) and are found in a diversity of habitats. Harbor seals in Alaska, USA, similar to Arctic pinnipeds in many respects, rely upon glacial ice for pupping, mating, and molting. Just as climate change affects Arctic sea ice, tidewater glaciers are rapidly retreating in Alaska, reducing ice availability for harbor seals. An increased understanding of glacial vs. terrestrial harbor seals may reveal information important to conservation of harbor seals and Arctic pinnipeds, as effects of climate change continue. We compared foraging distances, activity budgets, diet, and body condition for seals captured at glacial and terrestrial sites in Glacier Bay, Alaska. Foraging strategies and activity budgets of seals using glacial ice differed substantially from seals using terrestrial sites. Glacial seals traveled significantly farther to forage (>40 vs. <5 km) and spent more time hauled out than terrestrial seals (26 vs. 11 to 16%). Diets of glacial seals were higher in pelagic fishes compared to diets of terrestrial seals that foraged primarily on intertidal/dem-ersal fishes. Body condition of seals was similar between habitats (p > 0.09) and suggests that costs of longer foraging trips for glacial seals may be offset by obtaining higher quality diets of pelagic fishes, which may allow seals to spend more time hauled out. During the brief lactation period, more time hauled out could result in more time available for the transfer of energy from adult females to dependent offspring.