Harbor Seals and the Changing Iceberg Habitats of Alaska

Harbor seals in Alaska’s icy fjords depend on icebergs calved from glaciers as essential habitats for birthing, raising pups, and molting. A recent study sheds light on how climate-driven changes in glacier dynamics influence the availability and characteristics of these floating platforms, impacting the seals’ survival strategies.

The Connection Between Seals and Glacier Behavior

Researchers focused on Johns Hopkins Glacier in Glacier Bay National Park, Alaska, an advancing glacier unique among the majority of the world’s retreating glaciers. Thanks to a terminal moraine, a natural sediment barrier at its base, the glacier is insulated from warmer ocean waters, slowing its melting process. However, this also means that fewer icebergs are being produced, reducing the seals’ available habitat.

“We wanted to understand which of these areas seals were using and how this habitat is changing in response to advances at the glacier front and reduction in iceberg numbers,” explained Lynn Kaluzienski, a postdoctoral fellow at the University of Alaska Southeast who led the study.

Seals’ Seasonal Iceberg Preferences

Using time-lapse cameras, aerial surveys, and remote sensing, the research team tracked seal activity over several years. Their findings revealed seasonal patterns in iceberg utilization:

• Pupping Season (June): Female seals with newborn pups preferred slow-moving icebergs, drifting at speeds below 0.2 meters per second (7-8 inches per second). These stable platforms provided safer environments for vulnerable pups.

• Molting Season (August): Seals were more commonly observed on faster-moving icebergs, particularly near upwelling plumes of freshwater at the glacier’s base. These areas, rich in nutrients, attract plankton and fish, providing seals with optimal foraging conditions.

Iceberg Dynamics and Foraging Opportunities

When glaciers calve icebergs, their movement is dictated by wind, ocean currents, and freshwater plumes from the glacier’s base. These plumes, which are less dense than the surrounding saltwater, carry nutrient-rich particles that stimulate plankton growth—a food source that attracts fish and ultimately benefits the seals.

The study underscores the delicate balance between glacier dynamics and marine ecosystems. A decline in iceberg formation could limit the seals’ habitat, affecting their reproductive success and survival. While harbor seals demonstrate resilience by adapting to shifting conditions, their ability to cope has its limits.

The Future of Seals in a Changing Climate

As global glacier retreat accelerates, advancing glaciers like Johns Hopkins Glacier provide valuable insight into the interactions between ice dynamics and wildlife. However, even stable glaciers are not immune to environmental shifts. Reduced calving rates and altered iceberg characteristics highlight the need for ongoing research and conservation efforts to safeguard harbor seals and their fragile habitat.

For more information, visit the original study published by Interesting Engineering: Mama Seals Float on Slow, Steady Icebergs.