When swimming near large ships, Southern Resident Killer whales alter their behaviors because sounds broadcasted from boats interfere with the animals' ability to forage and communicate. It turns out whales are also greatly impacted by the speed at which a vessel is traveling, a recent study revealed.
Researchers from the University of Washington (UW) teamed up with the National Oceanic and Atmospheric Administration (NOAA) to examine how much noise produced by individual boats actually reaches whales in the inland waters of Washington and the British Columbia – areas that are home to an increasing number of ferries, whale watching cruises, fishing boats and shipping vessels.
"The goal was to understand this missing but assumed link between what we see at the surface and what the whales experience at depth," Juliana Houghton, lead author of the study and a recent graduate of the UW's School of Aquatic and Fishery Sciences, explained in a news release.
For their study, researchers attached temporary digital acoustic recording tags (DTAGs) to resident whales using suction cups. This allowed them to track the amount of boat noise reaching the animals. Additionally, the test area was monitored and a laser positioning system was used to track the size, speed and type of vessels traveling nearby.
"That combination allowed us to get accurate data on the distance to the whale from each vessel that was in the area, so we could understand how they contributed to noise exposure," Marla Holt, co-author and a NOAA Fisheries research scientist at the Northwest Fisheries Science Center in Seattle, added.
When comparing the characteristics of boats in the area to the sounds recorded by the hydrophones, researchers revealed the number of propellers and speed of a vessel increased the amount of noise disturbance.
Ultimately, this could impact the recovery of endangered resident killer whales, whose population now totals 80 animals. That's why researchers suggest federal regulations should enforce a speed limit in order to reduce noise exposure. Currently, however, regulations only require that vessels stay at least 200 yards away from whales and at least 400 yards out of the path of whales.
Their study was recently published in the journal PLOS ONE.
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