Ringed seals eat more and different prey close to Arctic glacier fronts
Understanding what marine mammals eat is genuinely difficult. Seals and whales feed underwater, across vast ocean distances, in conditions that resist direct observation. Most diet studies rely on stomach contents of stranded or dead animals - studies that cannot tell researchers where or when the animal last fed.
In the Arctic, Inuit communities hunt marine mammals as part of a subsistence lifestyle that has continued for millennia. Animals are harvested at known locations, at known times, with stomach contents that reflect feeding activity in the hours immediately before capture. For ringed seals, whose stomachs empty within a few hours, that combination of location data and stomach contents makes it possible to map feeding activity to specific ocean areas.
A study led by Project Assistant Professor Monica Ogawa from the National Institute of Polar Research in Japan, working with Inuit hunters around Inglefield Bredning in northwest Greenland, exploited exactly this approach. The findings, published in Communications Earth and Environment, revealed that glacier fronts function as concentrated feeding hotspots for ringed seals - and that the loss of those glaciers as Arctic warming accelerates could have cascading consequences for the ecosystem.
Glacier fronts as foraging hotspots
Ringed seals harvested close to tidewater glacier fronts - the points where glaciers meet the sea and calve icebergs - had notably fuller stomachs than those caught further away. The contents also differed: prey composition varied with distance from the glacier, indicating that seals feeding at glacier fronts target different species or use different parts of the water column than seals foraging elsewhere in the fjord system.
Tidewater glaciers create upwelling processes that bring cold, nutrient-rich water to the surface. This upwelling fuels dense concentrations of invertebrates and small fish - the prey that ringed seals, and through them the larger predators that depend on seals, rely on. The fuller stomachs and distinct prey composition at glacier fronts confirm that these upwelling zones function as foraging hotspots, concentrating prey and attracting seals from across the broader fjord system.
"Stomach content analysis is one of the most classical methods for studying animal diets. However, because stomach contents reflect only very recent feeding - within just a few hours for seals - this approach has often been seen as a limitation. We turned this limitation into an advantage by comparing what seals had eaten with where they were captured," said Dr. Ogawa.
What glacier retreat would mean for seals
As Arctic temperatures rise, tidewater glaciers are retreating. Many are pulling back from the coastline and becoming land-terminating glaciers that no longer extend to the sea. When a tidewater glacier retreats entirely onto land, the upwelling process that creates the feeding hotspot at the glacier front disappears with it.
The study warns that the disappearance of glacier-front foraging grounds could force seals to change their diet, distribution, and body condition. Seals with access to dense prey concentrations build fat reserves more efficiently than those forced to forage across larger, less productive areas. Changes in body condition affect reproductive success, survival rates, and ultimately population dynamics. Because seals are central prey for polar bears and a critical food resource for Inuit communities, those population dynamics matter far beyond the seals themselves.
"The findings revealed not only the importance of glacier fronts as feeding grounds for seals, but also that diet varies with distance from the glacier, indicating that the loss of these habitats could have wider consequences for Arctic marine ecosystems," the researchers noted.
Co-production with Inuit communities
This research could not have been conducted without the cooperation of Inuit hunters who provided both the harvested animals and their knowledge of where, when, and under what conditions the animals were taken. The spatial data - the critical link connecting stomach contents to foraging locations - came from subsistence harvesting, not from scientific expeditions. The researchers explicitly acknowledge that the quality and quantity of data they obtained would have been unachievable through scientific effort alone.
"This study was made possible through the cooperation of many Inuit hunters. By working together with Inuit communities, we could obtain data - both in quality and quantity - that scientists alone could never achieve," said Dr. Ogawa.
The study is limited to a single fjord system in northwest Greenland and a specific time period. Whether the patterns observed at Inglefield Bredning are representative of seal foraging ecology across the broader Arctic requires comparative data from other sites. The stomach content method captures only a few hours of feeding history, and individual seals may vary considerably in their use of different habitats.