Bowhead whales feed year-round in Cumberland Sound, Nunavut

Satellite telemetry and time-depth recorders are providing new and surprising insights into the secret lives of bowhead whales

Bowhead Whales live year-round in Arctic and sub-Arctic waters and are split into different geographic populations. One of these populations—the Eastern Canada – West Greenland population—generally summers in western Baffin Bay, the Canadian High Arctic, northern Foxe Basin, northwestern Hudson Bay and Cumberland Sound. Wintering is thought to occur in areas with less ice such as Hudson Strait.  

However, new research shows that at least one of these areas—Cumberland Sound (Nunavut, Canada)—is an important year-round feeding ground for bowhead whales.

In a recently published paper in the journal Marine Ecology Progress Series, University of British Columbia (UBC) Post-Doctoral Fellow Sarah Fortune reported the results of a 4-year study on the seasonal diving and foraging behaviors of Eastern Canada – West Greenland bowhead whales in Cumberland Sound.

Dr. Fortune and her team from Fisheries and Oceans Canada (Steve Ferguson, Justine Hudson and Bernard LeBlanc), Woods Hole Oceanographic Institution (Mark Baumgartner), and UBC (Valery LeMay and Andrew Trites) tracked 25 bowheads with satellite-linked time-depth telemetry tags to determine movements and dive behaviors. They also collected zooplankton samples in Cumberland Sound to determine prey species and biomass.

Prey sampling data suggested that the bowheads in Cumberland Sound were eating energy-rich Arctic copepods such as Calanus glacialis during summer. Dive depths were substantially shallower during spring and summer compared to fall and winter, and appear to correspond with seasonal changes in the vertical distribution of the copepods—which suspend development and overwinter at depth during fall and winter. 

The researchers also found that bowhead dive depths changed with time of day—providing evidence that their prey are migrating each day up and down the water column. Zooplankton avoid predation from visual predators by staying away from the sunlight surface waters during daylight, and move to the surface waters to eat phytoplankton at night. 

One of the big surprises of Dr. Fortune’s research was finding that bowhead whales resided in Cumberland Sound during all four seasons, with one animal remaining all year. Some of the whales she followed were infrequent visitors to Cumberland Sound, spending only a day to several weeks, while others had considerably longer residency times, spending several consecutive months in the area that occasionally included overwintering. However, peak bowhead occupancy occurred during summer and fall. 

The satellite telemetry locations also showed movement patterns indicative of feeding—suggesting that Cumberland Sound is a year-round feeding area. 

These findings provide a new understanding of the feeding behavior of bowhead whales, and the biological significance of Cumberland Sound to the Eastern Canada – West Greenland population.

Dr Sarah Fortune is a Post-Doctoral Fellow at the Marine Mammal Research Unit at the University of British Columbia

This research was made possible through the support of our community partners, Levi Qaunaq and Natalino Piugattak from Igloolik, and Noah Ishulutaq and Timeosie Akpalialuk from Pangnirtung, who were responsible for vessel operations. Logistical support was provided by the Igloolik and the Pangnirtung Hunters and Trappers Organizations and the Government of Nunavut. Bowhead whale data were collected under UBC ACC A14-0064 and Department of Fisheries and Oceans License to Fish for Scientific Purposes S-12/13-1014-NU and S-13/14-1009-NU and Animal Use Protocol FWI-ACC-2012-034 and FWI-ACC-2013-018.

PUBLICATION

2020
Seasonal diving and foraging behaviour of Eastern Canada-West Greenland bowhead whales. Fortune, S. M. E., S. H. Ferguson, A. W. Trites, B. LeBlanc, V. LeMay, J. M. Hudson and M. F. Baumgartner. 2020. Marine Ecology Progress Series 643:197-217. 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. keywords     Climate change, zooplankton, prey availability, foraging behavior, biologging, state-space model, bowhead whale, copepods, Calanus