The impact of rising sea temperatures on an Arctic top predator, the narwhal

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.

Behavioral Response Study on Seismic Airgun and Vessel Exposures in Narwhals

“…To elucidate whether seismic exposure affected the whales' selection of wintering ground a few months later, we compared their winter locations with those of 12 reference whales instrumented in 2010-2016 (see Heide-Jørgensen et al, 2015;Chambault et al, 2020).…”

Analysis of narwhal tusks reveals lifelong feeding ecology and mercury exposure

“…7 Changes in sea-ice dynamics will also influence the spatiotemporal movement patterns of narwhal. 25 Thus, environmentally driven changes in the temporal feeding ecology of narwhal can occur through either changes in food web composition or accessibility to different prey through changes in migration patterns. It is unclear which mechanisms are the primary drivers of the observed variability in feeding ecology of narwhal in our study, yet most processes are likely to be strongly influenced by climate change.…”

Bowhead whales overwinter in the Amundsen Gulf and Eastern Beaufort Sea

“…It is not clear if this pattern of movement was attributable to warmer water temperatures or related to the 2018-2019 overwintering event. Such strong avoidance of warm waters have also been recently demonstrated in narwhals in the eastern Arctic [51,52]. If the avoidance of warm ocean temperatures were the primary driver of this anomalous behaviour, it may be a significant warning sign for bowhead whales.…”