Impact of glacier and fjord dynamics on seal habitat

Abstract

Tidewater glacier fjords are highly dynamic environments that are affected by several glaciological and oceanographic processes: (i) subglacial discharge creates upwelling plumes that drive estuarine circulation and promote submarine melting of glaciers and icebergs, (ii) iceberg calving, which is affected by submarine melting, is a stochastic energy source that mixes near-glacier waters and produces waves that crash on shore and cause icebergs to capsize, and (iii) motion of icebergs and fjord waters are affected by winds, tides, and subglacial discharge. Biologists and glaciologists working in fjords have not traditionally worked together, and consequently little is known about the impact of these processes on fjord ecosystems. Numerous species reside in tidewater glacier fjords, including harbor seals, which seasonally aggregate in fjords and use ice habitat for critical life functions including pupping, molting, and foraging. Seals that haul-out on icebergs during the pupping and molting seasons take longer and deeper dives for feeding than those that use terrestrial haul-outs, but may acquire higher quality food. Additionally, icebergs do not flood during high tide, which increases the amount of time that seals can remain hauled-out and that pups can spend nursing, thus increasing energetic intake. Many basic questions remain unanswered, and the energy costs of coping with a constantly evolving landscape are unknown. This project addresses these deficiencies by investigating the temporal and spatial variability of seal habitat in Johns Hopkins Inlet, Glacier Bay, by synthesizing aerial surveys with high-rate time-lapse photogrammetry. Advances in camera and computer technologies have only recently made this type of observational survey possible. Results from this study will be of interest to biologists, glaciologists, and oceanographers working in fjords in the North Pacific and around the world, and will be of particular interest to National Park Service (NPS) employees that are responsible for wildlife management.