KILLER WHALE RESEARCH
THE QUESTION
The poor body condition of southern resident killer whales points to them not being able to obtain enough of their preferred prey (Chinook salmon) to meet their daily needs. This may be due to reduced abundance, accessibility and/or quality of salmon caused by fishing or environmental change. Another theory is that killer whales cannot access the prey that are available because of interference from vessel traffic and acoustic disturbance. We are testing whether reduced foraging success of southern resident killer whales is a function of less abundant and/or deeply aggregated (i.e., less accessible) prey.
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As a postdoctoral fellow at the University of British Columbia, I designed and carried out a comparative foraging ecology study with Drs. Andrew Trites and Mei Sato (Marine Mammal Research Unit). The goal of the study is to quantitatively determine whether there is sufficient Chinook salmon to support a healthy southern resident killer whale population.
THE APPROACH
We used underwater and aerial technology to study the fine-scale behaviour of killer whales, while hydroacoustics specialists simultaneously collect information about the quality and quantity of encountered prey. High-resolution behavioural data is collected using suction-cup attached Customizable Animal Tracking Solutions tags. These tags have an array of sensors including 3D accelerometers that are used to determine when a whale successfully catches a fish. The tags also have a forward facing camera used to identify the species of fish caught, the proportion of fish consumed and quantify prey-sharing events. A built-in hydrophone is used to record whale vocalizations, which helps determine the behavioural state of the whale (e.g., hunting, socializing etc). Through collaboration with Hakai Institute (Keith Holmes) we simultaneously collect aerial video of killer whales using an Inspire 2 drone to quantify behaviour near the surface. During our behavioural data collection, a multi-frequency echosounder was used to map the prey field. This instrument uses sound, just as killer whales use echolocation to find fish, and tells us how many fish are present, their relative size and the depths they occur.
Combining information about the feeding behaviour and encountered prey fields of healthy (northern residents) and unhealthy populations (southern residents) will allow us to gain a better understanding of whether southern residents are prey limited in British Columbian waters. We hope that the results of this study will ultimately be used to help inform future management decisions to aid in the recovery of this endangered population.
