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The Arctic is one of the most rapidly warming regions on Earth, raising concerns about cascading effects on the interconnected relationships among the environment, marine ecosystems and their apex predators - marine mammals - and Indigenous communities that depend on them as vital resources.
To assess and predict the impacts of climate change across this entire network, particularly on marine mammals and local people, which are at the top of this chain, I peered into these connections during the open-water season in Inglefield Bredning, home to Greenland’s northernmost Inuit communities, by combining analyses of biological samples with interviews with Inuit people who possess deep knowledge of the local nature and animals. During summer, four spices of marine mammals, including ringed seal (Pusa hispida), harp seal (Pagophilus groenlandicus), bearded seal (Erignathus barbatus) and narwhal (Monodon monoceros) inhabit this area and are important targets for Inuit hunters.
In chapter 2, I report on their feeding ecology and niche overlap among marine mammals revealed by stomach contents and stable isotope of livers and muscles collected between 2022 and 2024 to provide insights into the relationships between marine mammals and their prey. Polar cod (Boreogadus saida), the most abundant fish in the Arctic, was the dominant prey for marine mammals. Red fish (Sebastes fasciatus), an Atlantic fish typically found in more southern waters, was found from the stomachs for the first time in this region, and the composition of zooplankton showed a shift toward Atlantic species compared to previous studies, suggesting that climate change is driving changes in the marine ecosystem in this area. It was suggested that the narwhal has the narrowest dietary niche, making them the most vulnerable marine mammals in this region to environmental changes.
In chapter 3, I combined the stomach contents revealed in chapter 2 with location data of where each animal was hunted to conduct a spatial analysis of stomach contents to identify where they feed on polar cod. The results indicated that bearded seals establish a unique feeding niche in shallow waters, while the other mammals mitigate competition by adjusting their feeding areas based on the distance to glaciers. The glacial retreat due to climate change is potentially altering predator-prey interactions and interspecific competition, but the extent of these impacts may vary depending on their feeding areas and the degree of competition, even among sympatric species depending on the same prey.
In chapter 4, I focused on the foraging ground of ringed seals, which particularly uses glacier front as foraging grounds. By comparing data collected in 2003 with the results of this study, we investigated changes in foraging areas over the past 20 years and examined the impact of glacier retreat on their foraging ecology. Over the past two decades, seals have been foraging closer to glaciers, likely due to increased glacial runoff enhancing marine productivity around glacier fronts.
In chapter 5, I reported the trophic levels of organisms in the food web, from zooplankton to marine mammals, and the contaminant levels in the marine mammals which is accumulated through the food web. Contaminant concentrations were highest in narwhals, suggesting that they area a primary source of contaminant exposure for local people.
In chapter 6, I conducted interviews with local Inuit to incorporate knowledge beyond animal sample analysis, including their deep knowledge built from their lived experiences over the past decades, as well as intergenerational knowledge passed down generations. The most significant change which has been recognized by people was the melting glaciers, sea ice, and ice bergs, which have particularly impacted dog sled hunting, making it increasingly difficult to carry out traditional marine mammal hunting methods. Moreover, what became clear through listening to their stories is that global societal changes may have indirectly, yet significant impacts on their culture and marine ecosystems - Inuit people in this area are straggling in the midst of two changes, a changing environment and societal transformations.
This study comprehensively reveals the connections between the marine ecosystem, environment, and people in the region for the first time with a focus on marine mammals, and provides crucial insights for evaluating and predicting potential impacts of climate change.
Results of the study clearly revealed that for both marine mammals and the Inuit people who rely on them as vital resources, climate change is indeed a threat, and there is an urgent need to strengthen resilience to environmental changes in the region. In this study, I focused on the summer period when the only season the sea opens in this region. However, since climate change has been found to particularly affect sea ice condition, it is also necessary to investigate the conditions during the period when the sea freezes. I emphasize that, as the impacts of climate change on the environment, marine ecosystems, marine mammals, and local communities are interconnected, multifaceted, and complex, it is essential to approach the issue from multiple perspectives and interdisciplinary ways in devising effective strategies.
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