Climate change is affecting almost all regions and ecosystems. Particularly in the Arctic, where rapid sea-ice loss and increasing temperatures are altering the distribution and abundance of low trophic-level organisms, generating cascading effects through the entire food chain from phytoplankton to big mammals.

Narwhals (Monodon monoceros) are a species of cetaceans distributed from the Canadian Arctic Archipelago to East Greenland, Svalbard and the western part of the Russian Arctic. These are considered to be among the most sensitive of all Arctic endemic marine mammals to climate change due to their limited prey selection, strict migratory patterns and high site fidelity.

To study the impact of climate change on the population dynamics of narwhals, researchers in Greenland tracked the location of 144 individuals of this species via satellite from 1993-2019 in the Canadian Arctic Archipelago, West and East Greenland, which they related to variation in sea surface temperature in the same time period. They also studied the relation between the abundance of narwhals in 17 locations where they spend the summer (reported in previous studies) and trends in sea surface temperature at these locations.

This study showed that there is a higher abundance of narwhals in places where the sea surface temperature is lower, while in regions where an increase in temperature has been registered, populations are smaller. Other recent studies have revealed great abundance of narwhals in places where, despite little research, there was very little or no record of this species. Narwhals avoid waters above 2 °C, as they have a blubber insulation that prevents loss of body heat, and they also lack a dorsal fin (unlike other non-endemic Arctic whales). This morphological adaptation, which allows them to travel in ice-covered areas, can become a handicap facing warmer temperatures since it does not allow the dissipation of increasing heat. These results suggest that warming ocean waters will restrict the narwhal’s habitat range, as some populations may be under pressure to abandon their traditional habitats and migrate further North, or some populations may even go locally extinct. However, the trend of habitat change by narwhals is difficult to assess as some of the populations are part of the local subsistence harvest and are also prey for top predators like orcas, which has influences population dynamics.

A previous study conducted on bowhead whales (Balaena mysticetus) in the same region had obtain similarresults and suggests a limited thermal preference of Arctic cetaceans. Additionally, increasing water temperatures and sea-ice loss are expected to strongly modify the seasonality, distribution, and concentration of their prey. Thus, this increase in temperature can represent a great challenge for Arctic marine mammals.

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Source: Chambault, P., Tervo, O.M., Garde, E. et al. The impact of rising sea temperatures on an Arctic top predator, the narwhal. Sci Rep 10, 18678 (2020). https://doi.org/10.1038/s41598-020-75658-6

Author: Diana Rodrigues