Seasonal diving and foraging behaviour of Eastern Canada-West Greenland bowhead whales

Abstract

Climate change may affect the foraging success of bowhead whales Balaena mysticetus by altering the diversity and abundance of zooplankton species available as food. However, assessing climate-induced impacts first requires documenting feeding conditions under current environmental conditions. We collected seasonal movement and dive-behaviour data from 25 Eastern Canada-West Greenland bowheads instrumented with time-depth telemetry tags and used state-space models to examine whale movements and dive behaviours. Zooplankton samples were also collected in Cumberland Sound (CS) to determine species composition and biomass. We found that CS was used seasonally by 14 of the 25 tagged whales. Area-restricted movement was the dominant behaviour in CS, suggesting that the tagged whales allocated considerable time to feeding. Prey sampling data suggested that bowheads were exploiting energy-rich Arctic copepods such as Calanus glacialis and C. hyperboreus during summer. Dive behaviour changed seasonally in CS. Most notably, probable feeding dives were substantially shallower during spring and summer compared to fall and winter. These seasonal changes in dive depths likely reflect changes in the vertical distribution of calanoid copepods, which are known to suspend development and overwinter at depth during fall and winter when availability of their phytoplankton prey is presumed to be lower. Overall, CS appears to be an important year-round foraging habitat for bowheads, but is particularly important during the late summer and fall. Whether CS will remain a reliable feeding area for bowhead whales under climate change is not yet known.

Bowhead whales use two foraging strategies in response to fine-scale differences in zooplankton vertical distribution

“…For example, we found that while in Kingnait Fiord, SPLASH tagged animals partitioned their time between shallow Square (25 m) and U-shaped (30 m) dives and deep Square (267 m) and U-shaped ( 242 m) dives, which has been similarly observed for North Atlantic right whales in the Great South Channel 45 . The predominance of deep feeding dives recorded from SPLASH tagged animals is likely associated with the ontogenetic vertical migration of copepods, while the shallow dives may be focused on copepods that have not yet entered diapause (consistent with previous investigations of bowhead whale dive depth by month in Cumberland Sound 46 ). Furthermore, we found that fine-scale tagged animals also alternated between shallow and deep probable foraging dives where several shorter, shallow dives typically followed single long deep dives.…”

Residency and movement patterns of Cuvier’s beaked whales Ziphius cavirostris off Cape Hatteras, North Carolina, USA

“…We retained every 10 th sample to reduce within-chain sample autocorrelation (Jonsen 2016), for 2000 final posterior samples which we used to calculate model parameters and estimated loca-tions. Based on the results of previous studies, we considered behavioral state values of <1.25 as transit behavior, those >1.75 as ARS, and intermediate values between 1.25 and 1.75 as uncertain (Jonsen et al 2007, Bailey et al 2009, Kennedy et al 2014, Acuña-Marrero et al 2017, Fortune et al 2020.…”

“…ARS is associated with frequent course reversals and relatively slow swim speed, whereas transit behavior has higher rates of movement with increased persistence between locations (Jonsen 2016). Across studies of many different animal taxa, foraging has been inferred from ARS behavior, in which animals slow their horizontal movement speeds and increase turning rates in highly productive areas (Fortune et al 2020). Animals are believed to spend more time in a particular area if they are foraging successfully (Fortune et al 2020).…”

“…Across studies of many different animal taxa, foraging has been inferred from ARS behavior, in which animals slow their horizontal movement speeds and increase turning rates in highly productive areas (Fortune et al 2020). Animals are believed to spend more time in a particular area if they are foraging successfully (Fortune et al 2020). It is possible that ARS could include behaviors such as breeding or resting (Bailey et al 2009).…”

Developing a Precautionary Management Approach for the Eastern Canada-West Greenland Population of Bowhead Whales (Balaena mysticetus)

“…Within this range, individuals travel extensively while following the seasonal growth and ablation of sea ice (Eschricht and Reinhardt, 1866;Reeves et al, 1983;Ferguson et al, 2010;Nielsen et al, 2015). During the late summer and late autumn periods, feeding is concentrated on large Arctic copepods most commonly along the outlets of fiords of eastern Baffin Island (Richardson et al, 1995;Chambault et al, 2018;Fortune et al, 2020b).…”