Abstract
Arctic top predators are expected to be impacted by increasing temperatures associated with climate change, but the relationship between increasing sea temperatures and population dynamics of Arctic cetaceans remains largely unexplored. Narwhals (Monodon monoceros) are considered to be among the most sensitive of Arctic endemic marine mammals to climate change due to their limited prey selection, strict migratory patterns and high site fidelity. In the context of climate change, we assume that the population dynamics of narwhals are partly influenced by changes in environmental conditions, with warm areas of increasing sea temperatures having lower abundance of narwhals. Using a unique large dataset of 144 satellite tracked narwhals, sea surface temperature (SST) data spanning 25 years (1993–2018) and narwhal abundance estimates from 17 localities, we (1) assessed the thermal exposure of this species, (2) investigated the SST trends at the summer foraging grounds, and (3) assessed the relationship between SST and abundance of narwhals. We showed a sharp SST increase in Northwest, Mideast and Southeast Greenland, whereas no change could be detected in the Canadian Arctic Archipelago (CAA) and in the Greenland Sea. The rising sea temperatures were correlated with the smallest narwhal abundance observed in the Mideast and Southeast Greenland (< 2000 individuals), where the mean summer sea temperatures were the highest (6.3 °C) compared to the cold waters of the CAA (0.7 °C) that were associated with the largest narwhal populations (> 40,000 individuals). These results support the hypothesis that warming ocean waters will restrict the habitat range of the narwhal, further suggesting that narwhals from Mideast and Southeast Greenland may be under pressure to abandon their traditional habitats due to ocean warming, and consequently either migrate further North or locally go extinct.
Highlights
Arctic top predators are expected to be impacted by increasing temperatures associated with climate change, but the relationship between increasing sea temperatures and population dynamics of Arctic cetaceans remains largely unexplored
Narwhals have been considered tightly associated with sea ice[14], and while this may be the case for some populations most narwhal populations spend 2–3 summer and fall months in ice-free areas but always in areas dominated by cold polar waters
To assess the influence of rising sea temperatures on narwhals we focused on the summer period which corresponds to peak of ocean temperatures in the Arctic
Summary
Arctic top predators are expected to be impacted by increasing temperatures associated with climate change, but the relationship between increasing sea temperatures and population dynamics of Arctic cetaceans remains largely unexplored. Narwhals (Monodon monoceros) are considered to be among the most sensitive of Arctic endemic marine mammals to climate change due to their limited prey selection, strict migratory patterns and high site fidelity. Arctic marine mammals have the potential to move over long distances to adapt to changing and erratic resource availability Their capacity to adjust long-term adaptations, like site-fidelity and fixed migratory patterns, to climate-induced perturbations remains poorly known[4,5]. Narwhals are generally considered to be among the most sensitive and vulnerable of Arctic endemic marine mammals to climate c hanges[15] due to their choice of habitat, limited prey selection, strict migratory patterns and high site fidelity. The contrasting oceanographic conditions encountered at the different summer grounds as well as the hunting pressure may explain the demographic variability for the species
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