After dark with the Southern Residents

Raincoast’s hydrophone deployed off of Pender Island captured nearly five hours of Southern Resident killer whale (SRKW) vocalizations during an overnight pass through Swanson Channel. The first calls were recorded on February 16 at 10:55 pm, with calls continuing intermittently until 3:47 am on February 17. For much of that time, the whales were echolocating, producing a series of rapid, high-frequency clicks used to locate their prey.¹

If you’ve never seen a spectrogram before, these figures let us visualize the sounds recorded by our hydrophone. Time (in seconds) is on the x-axis and frequency (kHz) is on the y-axis. In this first clip, there is little background noise, and killer whale calls show up clearly as stacked horizontal bands between 0-7 kHz. You can also see echolocation clicks as thin vertical lines at slightly higher frequencies. In these quieter moments, both the calls and clicks are easy to pick out.

But these recordings also tell another story. 

Several calls were interrupted or masked by noise from passing vessels, illustrating how human activity disrupts the acoustic environment these whales depend on. SRKW are highly social animals that rely on quiet oceans to communicate, coordinate behaviour, and track their prey. When vessel traffic increases, excess underwater noise can reduce foraging efficiency ^{2 3}, disrupt pod behaviours, or displace whales from their critical habitat ⁴

Overnight transits through the Southern Gulf Islands might be a strategic move by SRKW to reduce their exposure to vessel traffic and excess noise. While commercial vessels operate around the clock and are difficult to avoid, recreational, ecotourism, and passenger vessels are most active during daylight, especially in summer, when tourism peaks and more people are on the water.

As efforts to reduce underwater noise continue, these recordings provide a clear record of human-caused disturbance. Yet they also capture rare moments of relative quiet, windows between ships when these whales can communicate and forage with fewer acoustic barriers. For SRKW, sound is critical to their survival. Ensuring they have access to a quiet ocean is essential to supporting their recovery.

1. Barrett-Lennard LG, Ford JKB, Heise KA. 1996. The mixed blessing of echolocation: differences in sonar use by fish-eating and mammal-eating killer whales. Animal Behaviour. 51(3):553–565. doi:https://doi.org/10.1006/anbe.1996.0059.
2. Tennessen JB, Holt MM, Wright BM, Hanson MB, Emmons CK, Giles DA, Hogan JT, Thornton SJ, Deecke VB. 2024. Males miss and females forgo: Auditory masking from vessel noise impairs foraging efficiency and success in killer whales. Global Change Biology. 30(9) doi:https://doi.org/10.1111/gcb.17490.
3. Holt MM, Tennessen JB, Hanson MB, Emmons CK, Giles DA, Hogan JT, Ford MJ. 2021. Vessels and their sounds reduce prey capture effort by endangered killer whales (Orcinus orca). Marine Environmental Research. 170:105429. doi:https://doi.org/10.1016/j.marenvres.2021.105429.
4. Lusseau D, Bain D, Williams R, Smith J. 2009. Vessel traffic disrupts the foraging behavior of southern resident killer whales Orcinus orca. Endangered Species Research.