In frigid areas, harbor seals utilize icebergs that calve from glaciers as secure spots for birthing, raising their pups, and molting. Recent research reveals that as glaciers evolve due to climate change, variations in iceberg size, movement, and quantity influence the essential icy habitats for seals. Mother seals are inclined to choose stable, slower icebergs for giving birth and nurturing their young, whereas during the molting period, they and the rest of the seal community gravitate towards faster ice near optimal feeding zones.
“Our research establishes a clear connection between glacier movement and the behavior and distribution of seals,” stated Lynn Kaluzienski, a postdoctoral fellow at the University of Alaska Southeast who spearheaded the study. “Interdisciplinary research combined with extended monitoring efforts are vital for comprehending how climate change will impact tidewater glacier fjord ecosystems in the coming years.”
Kaluzienski will share the study’s conclusions at the AGU’s 2024 Annual Meeting in Washington, D.C., on Tuesday, December 10.
The research concentrated on harbor seals and icebergs in Johns Hopkins Inlet and Glacier, situated within Glacier Bay National Park, Alaska. Notably, Johns Hopkins is among the few glaciers on Earth that is experiencing advancement (becoming thicker and moving forward into the fjord) rather than retreating as a result of global warming, partly due to its terminal moraine of crushed rock and sediment. This formation effectively blocks warmer ocean waters that would otherwise accelerate the glacier’s melting.
However, this sediment barrier decreases the quantity of icebergs calved by the glacier into the fjord. A reduction in icebergs translates to diminished habitats for seals, underscoring the importance of understanding how seals interact with the available icebergs.
Kaluzienski, along with university peers and U.S. National Park Service collaborators, has spent recent years documenting detailed changes in both icebergs and seal distribution within the fjord, employing time-lapse cameras and aerial photography.
“Icebergs can be found in various parts of the fjord, particularly in areas of rapid flow, within eddies, and near the glacier,” Kaluzienski explained. “We aimed to determine which of these locations seals utilized and how this habitat is evolving as the glacier advances and iceberg numbers shrink.”
Once an iceberg breaks off from a glacier, its velocity and trajectory are influenced by wind, ocean currents, and freshwater runoff from the glacier’s base. This runoff, termed a plume, is lighter than the saline water in the fjord and carries plankton and fish to the surface, creating a moving food source for seals to access from icebergs.
The research team employed remote sensing data to identify the plume and analyzed its relation to iceberg and seal locations during the pupping season in June and molting season in August. They discovered that in the pupping season, seals typically found on land were situated on slower-moving icebergs, moving at speeds below 7-8 inches (0.2 meters) per second. On the other hand, the molting season saw seals increasingly residing on faster-moving icebergs located near the plume.
It is possible that slower-moving icebergs provide more stability, offering a solid platform for adult seals to tend to their young. This stability might be less vital during the molting phase, where icebergs close to the plume provide enhanced foraging possibilities.
