Transient orcas on the move

Each year, around April time, killer whales approach the Oregon coast and patrol the central coastal waters, looking for baby gray whales, sea lions or seals to feast on. They are rarely seen in these waters, except at this time of year. These particular whales are known as “transient” whales and little is known about them except they are more predatory and don’t think twice about killing the gray whale calves who are migrating through the area with their mothers.

The whales can stay in the area for weeks but it all depends on what food source is around. They are also seen teaching their own younger animals how to hunt. Transient killer whales tend to be very quiet while travelling and foraging, and can often pass by a hydrophone without being detected. This could be because their prey - sea lions, seals etc have ears and would be able to hear the whales approaching if they were making noise. However, when they are attacking and killing prey, transients become quite vocal.

The diet of transient whales consists almost exclusively of marine mammals - they rarely eat fish. However one theory about why the whales have been more frequent in these waters in recent decades is that the sardine population has recently begun to recover from over fishing in the 30’s. The whales have been seen swimming around huge sardine balls with great frequency, forcing them to join together even closer. Then, the whales swim through them with their mouths open, feeding on hundreds of the small fish.

Unlike resident killer whales, transients may not always stay together as a family unit and pods consist of smaller groups.

Images (c) James Dorsey