Harbor seals in Alaska’s Glacier Bay National Park exhibit fascinating behavior when selecting icebergs, choosing their icy platforms based on the time of year, according to new research presented at the American Geophysical Union’s annual meeting. This unique adaptation is crucial in a dynamic environment shaped by the advancing Johns Hopkins Glacier, one of the few glaciers globally bucking the trend of retreat. The glacier’s advance, however, limits the number of icebergs in the fjord, impacting the seals’ habitat.
This study delves into the strategic iceberg selection of harbor seals (Phoca vitulina) throughout the year, providing valuable insights into their behavioral ecology. The Johns Hopkins Glacier’s unusual advancement within Glacier Bay National Park creates a unique setting for this research.
“Icebergs are distributed throughout the fjord in various locations – areas of fast flow, within eddies, and near the glacier,” explains Lynn Kaluzienski, lead author of the study and researcher at the University of Alaska Southeast. “Our goal was to determine which areas seals prefer and how these habitats are changing due to the glacier’s advance and the resulting decrease in iceberg availability.”
The research revealed distinct seasonal preferences in iceberg selection. During pupping season in June, harbor seals favor slower-moving icebergs, typically drifting at speeds of 7 to 8 inches (0.2 meters) per second. This preference likely provides a more stable platform for mothers and their vulnerable pups.
However, as the season shifts to August and molting begins, the seals’ priorities change. They gravitate towards faster-moving icebergs located closer to the plume, a nutrient-rich zone where glacial runoff and ocean currents converge. This area is teeming with plankton and fish, providing a readily available food source for the seals during the energy-intensive molting period.
The researchers hypothesize that the slower-moving icebergs provide crucial stability for nursing mothers and their pups in early summer. As molting season approaches, stability becomes less critical, and the faster-moving icebergs near the plume offer easier access to abundant food resources.
“Our findings directly link the glacier’s advance to seal distribution and behavior,” Kaluzienski states. “Interdisciplinary studies like ours, combined with long-term monitoring, are essential for understanding how climate change will affect tidewater glacier fjord ecosystems.”
Climate change poses a significant threat to these delicate ecosystems. A recent AI-driven analysis of 10 climate models highlights the potential for substantial warming in many regions globally, adding further urgency to understanding and mitigating its impact on vulnerable species like harbor seals.
This study contributes valuable knowledge about the adaptive behaviors of harbor seals in a changing environment. While the reduction in iceberg numbers due to the glacier’s advance presents a challenge, understanding their strategic iceberg selection provides a crucial baseline for future monitoring and conservation efforts. The research underscores the importance of continued observation and interdisciplinary studies to protect these unique creatures and their fragile habitat in the face of climate change.
