Glaciers Serve as a Key Habitat for Harbor Seals

Harbor seals on glacial ice (Source: Jamie Womble/NPS).

To someone flying a small, fixed-wing aircraft over Alaska, the harbor seals far below contrast sharply against the brilliant white of the glacial ice. The seals vary in size, but they all share a similarity: they’re using the ice as a refuge to haul-out. This behavior is critical to their survival and involves laying outside of the water for a number of hours to regulate their body temperature. A recent study published in the journal of Marine Mammal Science found that harbor seals depend on icebergs more than previously thought. These icebergs are formed by glaciers that calve into the ocean, and the free-floating ice is used by harbor seals to haul themselves out from the surrounding water.

The study was conducted along the southeastern coast of the Kenai Peninsula in Alaska. It shows the comparison between glacial and terrestrial (land) haul-outs. The research found that pupping is preferred at glacial haul-outs, with molting seals frequenting both the terrestrial and lake ice habitats that are affected by tides.

The location of the study area. The red highlighted coast illustrates the geographic extent of the surveys (Source: Marine Mammal Science).

The findings were supported by extensive data collected on nine tidewater glaciers and their surrounding areas, primarily from aerial surveys from 2004 to 2013. The research was supplemented by vessel-based surveys and field and video observations.

Harbor seals, or Phoca vitulina, can dive hundreds of feet and remain underwater for up to 40 minutes, according to the Seal Conservancy. To compensate for their time spent underwater, they must haul-out for seven to twelve hours during the day to regulate their body temperature properly. This need for rest increases during molting or pupping season in the winter and spring months, when extra heat, rest, or nursing is necessary. Glacial ice habitats were found to be especially important for pupping, even when the distance to foraging is increased, because prey is easier caught in locations farther away.

“Glacial habitats are fascinating, dynamic and beautiful locations. In healthy ice conditions, ice provides secluded haul-out locations that seals prefer. In addition, ice habitats temper sea conditions so that seals are able to spend extended periods on ice, rather than the few hours that tidally washed rocks and beaches allow for,” Anne Hoover-Miller, a harbor seal researcher and author of the study, told GlacierHub.

Glacial habitats are notably variable as the floating ice is dependent on the size and frequency of calving events (ice breaking off from the glacier’s face), displacement by winds and currents, and melting— all elements that can be affected by climate change. According to the U.S. Geological Survey, most glaciers in Alaska are “retreating, thinning, and stagnant,” so the seals’ dependence on glacial habitat is alarming to researchers. The study found a pattern of reduced calving at tidewater glaciers and reduced ice in late summer, which the authors believe is leading harbor seals to use alternative haul-outs.

A harbor seal in nearby Valdez, Alaska, using a patch of glacial ice to haul-out (Source: Frostnip Photography/Creative Commons)

The Kenai Fjords are also subject to vessels passing by, which disturb the seals that lie upon the icebergs. Ships cause seals to end their haul-out prematurely and retreat to the apparent safety of the waters. The study speculates that the abundance of vessels may also have potential consequences for the use of glacial ice habitats, in a broader sense. This may be exacerbated when the effects of tourism on habitat quality are considered.

“The scientific community is gaining a better appreciation of subtle effects tourism and vessels have on seals,” said Hoover-Miller, stressing the importance of human adaptation efforts to preserve stable environments for the seals. “It is prudent to help vessel operators to minimize adverse impacts and stress on the seals.”

Harbor seals associated with glacial and terrestrial habitats did exhibit flexibility when it comes to choosing haul-out, pupping, and molting habitat, depending on the availability of glacial ice. “This concept, however, needs additional study,” noted Hoover-Miller. This behavior is in contrast to the often sedentary nature that is attributed to these pinnipeds.

The journey of discovery may provide a greater understanding on harbor seals’ glacial haul-out habitats and the effects of glaciers on larger marine habitats. Harbor seals are increasingly facing the combined impacts of climate change and tourism, which concerns researchers like Hoover-Miller. She would like to see future research regarding “greater development in multi-year telemetry that will give us a better understanding of the breadth of responses seals have when adapting to seasonal and climate driven changes in their habitats during their lifetime.”

To learn more about harbor seals and their tidewater glacier habitats, check out another one of GlacierHub’s articles on the topic.