Human-Made Noise in Salish Sea Threatens the Survival of Southern Resident Orcas
Research shows that underwater noise from vessels interferes with orca echolocation, disproportionately affecting females and contributing to the slow recovery of critically endangered southern resident orcas in the Salish Sea.
New Study by University of Washington Reveals Noise Pollution is Hindering Orcas’ Ability to Hunt Salmon, Exacerbating Their Endangered Status
A new study by the University of Washington and the National Oceanic and Atmospheric Administration (NOAA) sheds light on the impact of underwater noise pollution on the hunting behaviors of resident orcas in the Salish Sea, revealing why southern resident orcas continue to face challenges in their recovery. The study, published on September 10 in Global Change Biology, highlights the significant role human-induced noise plays in disrupting the lives of these critically endangered creatures.
The Salish Sea, encompassing coastal waters in Washington and British Columbia, is home to two distinct populations of orcas: the northern resident and southern resident orcas. While the northern residents have seen a steady population growth, the southern resident orcas remain endangered, with their numbers plateauing at around 75 individuals.
Human activity throughout the 20th century—including the reduction of salmon populations and the capture of orcas for entertainment—significantly harmed both orca populations. The introduction of underwater noise pollution in recent decades has exacerbated the already precarious situation, making it even harder for these intelligent marine mammals to hunt for their primary prey, salmon.
The study used data collected from 2009 to 2014, during which researchers placed “Dtags” on orcas—non-invasive digital tags affixed with suction cups that tracked their three-dimensional movements, hunting attempts, and the noise levels they encountered. Findings show that noise from vessels, especially boat propellers, interferes with the orcas’ echolocation, a critical tool they use to detect, pursue, and capture fish. Even a slight increase in ambient noise decreased the orcas’ hunting success.
Jennifer Tennessen, lead author and senior research scientist at the University of Washington’s Center for Ecosystem Sentinels, noted that the negative effects of noise are particularly severe for southern residents, who spend more time in areas of the Salish Sea with high vessel traffic. “It shines a light on why southern residents in particular have not recovered. One factor hindering their recovery is the availability and accessibility of their preferred prey: salmon. When you introduce noise, it makes it even harder to find and catch prey that is already hard to find,” said Tennessen.
In addition to impacting the overall hunting process, the study revealed that noise pollution disproportionately affects female orcas, who are less likely to pursue prey under noisy conditions. Researchers hypothesize that this may be due to concerns for calves left at the surface during extended hunting attempts, or the need for lactating females to conserve energy.
The research underscores the need for coordinated efforts to mitigate vessel noise in the Salish Sea. Voluntary speed-reduction programs on both sides of the U.S.-Canada border, such as the Echo Program in British Columbia and Quiet Sound in Washington, are helping to create quieter waters. However, Tennessen emphasized that reducing noise is only part of the solution: “When you factor in the complicated legacy we’ve created for the resident orcas — habitat destruction for salmon, water pollution, the risk of vessel collisions — adding in noise pollution just compounds a situation that is already dire. The situation could be turned around, but only with great effort and coordination on our part.”
Co-authors of the study include scientists from NOAA, Fisheries and Oceans Canada, Wild Orca, Cascadia Research Collective, and the University of Cumbria. The research was funded by NOAA, Fisheries and Oceans Canada, and the University of British Columbia, among others.
The findings are an urgent call to action, highlighting the need for sustained efforts to protect the southern resident orcas and ensure the continued recovery of their northern counterparts.
