New landmark research has revealed fascinating insight into killer whale feeding and foraging behaviours. The study – conducted by Vancouver Aquarium research scientist Dr. Lance Barrett-Lennard and a team of colleagues – documented gray whale predation by killer whales near Unimak Island, Alaska.
Killer whales have been known to be able to hunt, kill and consume whale species far larger than themselves. However, these events are rarely seen and reported, therefore making it hard to determine how common it occurs and what the impact might be on prey populations.
This study – Gray whale predation and prolonged feeding on submerged carcasses by transient killer whales at Unimak Island, Alaska – culminates four years of observation and describes the behaviour of a newly-discovered population of killer whales at the boundary of the Pacific Ocean and Bering Sea.
The dramatic impact killer whales have on other aquatic life, including threatened gray whales, is becoming evident through direct observation. Scientists are beginning to understand the effects they have on their prey and indirect impacts they have on marine communities.
Since 2002, Barrett-Lennard and Alaskan researcher Craig Matkin have been at the forefront of a long-term research project on killer whales along the Alaskan Peninsula. This project highlights the Vancouver Aquarium’s 30-year tradition of cetacean research – playing a central role in the world’s longest continuous study of killer whales in B.C.
The research team made the following discoveries:
- Over 150 transient killer whales gather every spring near Unimak Island, Alaska, when gray whales are heading north on their annual migration.
- For a month or more, the killer whales hunt and feed exclusively on gray whale calves and yearlings.
- The gray whales’ principal defense is to move into very shallow water along the shoreline, where killer whales are reluctant to press the attack. The killer whales also give up when mothers defend their calves particularly aggressively.
- Most gray whales are attacked in waters of 10-20 m depth and sink to the bottom after death.
- After an initial feeding period, killer whales leave the site for 24 hours or more before returning to feed again—the first time such food storing behavior has been reported in whales.
- Stored carcasses leave a tell-tale sheen of oil on the surface that may persist for up to a week.
- Gray whales killed by killer whales provide an important source of food for other predators, including Alaskan brown bears and sleeper sharks.
To learn more about Lance Barrett-Lennard’s study and research, visit this website.