BOWHEAD WHALE BODY CONDITION IN A CHANGING ARCTIC ECOSYSTEM

Abstract

Climate-induced changes, particularly ocean warming and sea ice loss, may alter primary and secondary productivity in the Arctic Ocean, with cascading bottom-up effects for higher consumers. However, it is unknown how shifts in prey quality and quantity will impact the foraging success of bowhead whales (Balaena mysticetus) from the Eastern Canada-West Greenland (EC-WG) population. To assess the foraging success of the EC-WG bowhead whale population, I calculated body area index (BAI) as a metric of body condition using photogrammetric measurements obtained from 463 individuals. Aerial drone imagery (images and/or videos) were collected during summer over eight years (2016-2023) from Cumberland Sound (a foraging area), Nunavut. My objectives were to 1) compare the BAI of different age-sex groups to determine which EC-WG population segments were vulnerable, and 2) examine whether interannual variability in BAI was correlated with any environmental variables (e.g., sea ice conditions, major climate indices) over time. When length-based age-class data was pooled, I found that the Cumberland Sound habitat favoured a larger proportion of immature whales (juveniles and subadults), with younger (or shorter) age-classes (calves, yearlings, juveniles) in better body condition than older age-classes (subadults and adults). By combining measurements with biopsy (sex and epigenetic aging) results, I also confirmed that there was a skew towards male (44:22) and sexually immature (1+ to 23 years of age) whales. While the annual mean BAI varied within a small range of value (~31-33), fluctuations corresponded with changes in oceanographic conditions. Using generalized linear models, I found that improvements in body condition were positively correlated with lagged (1 to 3 years) environmental variables, including sea ice phenology (freeze-up and sea ice duration) and a positive summer North Atlantic Oscillation index, with the latter linked to increases in secondary productivity. Year was negatively correlated with BAI, suggesting a potential decline over the short timeseries consistent with a reversal in NAO phase. Overall, my findings provide insight about the body condition of the recovering EC-WG bowhead whale population, including previously under-represented age-classes, and how changes in health may occur on delayed timescales following episodic events.