Cortisol levels in narwhal (Monodon monoceros) blubber from 2000 to 2019

Abstract

Narwhals (Monodon monoceros Linnaeus, 1758) summering on northern Baffin Island are experiencing increases in vessel traffic related to an iron-ore mine operated by Baffinland Iron Mines Corporation; how this increase in vessel traffic may impact narwhal is currently unknown. Cortisol is a stress response hormone and a stress indicator in marine mammals. This study evaluated cortisol levels in narwhal blubber sampled during subsistence harvests prior to project-related vessel traffic (2000–2006), during project-related vessel traffic (2013–2019), and during a high-stress entrapment event that occurred in 2015. There was a significant increase in cortisol levels from pre- (0.81 ± 0.45 ng/g (±SE)) to during (1.81 ± 0.48 ng/g (±SE)) project-related vessel traffic (over 100% higher), and both were significantly lower than cortisol levels from animals sampled during an entrapment event (10.52 ± 0.59 ng/g (±SE)). Increased vessel traffic, changing ice conditions, altered Arctic food webs, increased predation pressure from killer whales, and cumulative impacts from these sources likely all contribute to increased stress levels for narwhals. Thus, there is a need for continued monitoring of stress responses (i.e., cortisol levels) and other health indicators in narwhals to understand how individual fitness and the population will be impacted over time.