MARINE MAMMAL RESEARCH NEWSLETTER | February 2015 (Issue 12)
INTO THE FIELD
Fine-scale bowhead whale tagging and prey sampling
In August, UBC PhD Student Sarah Fortune and several thousand pounds of field gear headed north to Baffin Island to carry out her second field season. Her goal was to conduct a fine-scale bowhead whale tagging and prey sampling study in Cumberland Sound, Nunavut.
Cumberland Sound appears to have historically been a seasonally important habitat for bowhead whales, and also served as an important bowhead whaling ground in the Eastern Canadian Arctic. However, since receiving protection from whaling, the Eastern Canada-West Greenland bowhead whale population has been rebounding and researchers have been speculating why the whales are attracted to the area. One possibility is that this area shelters immature bowheads from killer whale predation. Another is that it serves as an important buffet site.
Sarah and her colleagues tested the hypothesis that Cumberland Sound is a seasonally important foraging ground for bowhead whales by equipping individual animals with short-term, non-invasive archival tags that record dive behavior and simultaneously collecting prey in the path of the tagged whale.
The collaborative research team consisted of local Inuit, a student from the Nunavut Arctic College, and government researchers (Fig. 1). The team successfully tagged four bowhead whales in Kingnait Fiord (the biggest fiord in Cumberland Sound) and sampled prey in areas where the whales dove.
The first whale they tagged (Fig. 2) traveled nearly 50 km into Kingnait Fiord in less than ideal weather conditions—rain and fog. The tag continuously recorded the whale’s dive behavior; however, the tag archives data and must be retrieved before the data can be accessed. A radio signal in the tag was used to track the whale (Fig. 3) and to locate the tag when it was released from the whale by a corrosive release mechanism.
Sarah placed a directional hydrophone in the water and rotated it in a circular pattern while listening for the sound of the acoustic transmitter’s ping. Each time she heard the ping, she could determine the bearing of the whale and also get a measure of the whale’s dive depth in real-time. This sound of the ping was the only thing keeping the team connected to the whale—an ‘acoustic leash’.
While maintaining a maximum distance of 1 km from the tagged whale, Sarah recorded the location where the animal surfaced and dove and relayed this information to a second vessel collecting prey samples.
Food samples were collected using a fine-mesh net (Fig. 4) lowered to varying depths, and pulled back to the surface. The team found high abundances of zooplankton (the preferred prey of bowhead whales; small crustaceans about the size of grain of rice). So far, the samples collected near the whales have consisted primarily of four species of Calanoid copeods—Pseudocalanus spp., Calanus finmarchicus, C. glacialis and C. hyperboreus.
Overall, Arctic zooplankton species appear to represent the greatest total biomass and it seems likely that the whales are feeding mostly on Arctic zooplankton species that are large and high in energy content compared to smaller bodied temperate species of zooplankton (Fig. 5).
Once the tracking tags were retrieved and the data were downloaded, Sarah was able to examine the dive behavior of the tagged animals. Overall, it seems the whales spent a great deal of time searching for prey based on the number of V-shaped dives they made (Fig 6). However, several U-shaped dives were also recorded, during which whales spent a longer period of time at their maximum dive depth and were thought to be feeding.
Sarah and her colleagues are encouraged by the new insights they gained about bowhead whale prey and feeding behavior in Kingnait Fiord, and hope to return next summer to continue collecting valuable information about the diet and feeding strategy of these large marine predators.
This project has been made possible through collaboration and support provided by Dr. Steve Ferguson from Fisheries and Oceans Canada and Dr. Mark Baumgartner from Woods Hole Oceanographic Institution.