August 4, 2021 — The following was released by NOAA Fisheries:
Increased abundance of salmon in the inland waters of the Salish Sea increased the odds of endangered Southern Resident killer whales capturing salmon as prey, but increased speeds of nearby boats did just the opposite, according to new research findings.
The research was led by NOAA Fisheries’ Northwest Fisheries Science Center. It found that the orcas descended more slowly, and took longer dives to capture prey, when nearby boats had navigational sonar switched on. The sonar from private and commercial vessels directly overlaps the main sound frequencies the whales use to hunt. This may mask the whales’ signals and force them to expend more energy to catch prey.
“That suggests that it may prolong their effort to dive in search of prey, which like all marine mammals they have to do on a breath hold—so they can stay underwater only so long,” said Marla Holt, research wildlife biologist at the Northwest Fisheries Science Center and lead author of the new research. Researchers used suction-cup tags that record whale movements and sound to track and analyze their behavior and use of sound to hunt.
Earlier research found that the faster nearby vessels traveled, the greater noise the endangered killer whales experienced. That could help explain why higher speeds of nearby vessels were associated with reduced odds of the whales capturing prey. Faster vessels might also seem more unpredictable to the whales, possibly distracting them as they close in on prey, Holt said.
“Consequences of reduced food intake include negative impacts on the whales’ ability to meet their energetic requirements to support key life functions, including growth and reproduction,” the scientists wrote in the new research paper published in the journal Marine Environmental Research.