MEPS 525:273-285 (2015)  -  DOI: https://doi.org/10.3354/meps11202

ABSTRACT: Satellite tracking of animals can provide information on their foraging behaviour, behavioural flexibility, and potential prey. Differences in diet among narwhals Monodon monoceros from the Baffin Bay (BB), East Greenland (EG) and Northern Hudson Bay (NHB) populations have been detected using stable isotope analysis. Presumably, differences in diet should correspond to differences in dive behaviour among populations, which we evaluated using satellite-linked tags. Thirty-four narwhals were equipped with transmitters in order to evaluate the total number of dives and time spent in pre-defined depth categories. Repeated-measures ANOVAs found narwhals from EG made significantly more dives and spent more time in the mid-water column compared to other populations. NHB narwhals made more dives in the deep zone than in the mid-water region. BB narwhals spent time and made most dives within the upper water column and the deep zone, which suggests deep-dwelling prey may contribute substantially to their diet. Within the BB and EG populations there were sex-specific differences in time spent at depth and we identified seasonal changes in diving for all populations. This is the first study to compare dive behaviour in all 3 of the world’s narwhal populations. We found that dive behaviour differences among populations paralleled differences in diet. Results suggest that narwhals employ specialized foraging strategies, which have repercussions on their potential ability to adapt to ecosystem changes.

KEY WORDS: Narwhal · Monodon monoceros · Satellite tracking · Diving behaviour · Time at depth