To the human eye, big ships cruising along the west side of San Juan Island this summer might have looked like they were traveling in slow motion. To the perceptive ears of killer whales, those same ships might have sounded a little bit quieter.
(From Oregon Public Broadcasting/ By Allegra Abramo) — That’s because more than half of commercial ships transiting Haro Strait — between San Juan and Vancouver Island — voluntarily slowed down as part of a two-month experiment by the Port of Vancouver, British Columbia. The port wanted to test how slowing vessels reduces underwater noise — and whether that could help endangered killer whales.
On the noise front, the slowdown appears to be a success, according to the port’s preliminary analysis. Not only were participating ships quieter, but ambient underwater noise levels also fell by nearly half during the slowdown, which ran from Aug. 7 to Oct. 6.
But how did the resident killer whales respond to those slower, quieter ships?
A team of U.S. and Canadian scientists is now trying to answer that question. Their work could help determine whether enforcing vessel speed limits in the southern resident killer whales’ critical habitat — or other options such as sending ships through in a convoy — might buy the whales some time. The population fell this year to only 76 animals, a 30-year low.
Combined with dwindling salmon stocks and persistent chemical pollutants, noise is one of the top threats to the remaining resident orcas. The din from human activities makes it harder for the whales to catch scarce chinook salmon, their main prey. At the noisiest times in their critical habitat, southern resident killer whales can lose an estimated 97 percent of their opportunity to communicate in their close-knit pods, which is critical to coordinating their hunting, staying safe and finding mates.
The whale community rallies
Just weeks before the vessel slowdown was set to begin, oceanographer and ocean acoustics expert Scott Veirs realized it offered a rare chance to better understand how ship noise affects the whales by observing their behavior when ships passed at different speeds and noise levels. The Port of Vancouver planned to rely on computer models to predict the effect on the whales, rather than collecting new data on changes in the whales’ actual behavior in response to the slowdown.
Veirs and his father, retired physics professor Val Veirs, had already been eavesdropping on ships in local waters for about 15 years through a series of underwater listening stations on San Juan Island and around the Salish Sea. They teamed up with marine conservation biologist Rob Williams of the Oceans Initiative, whose observational studies have shown the whales spend less time foraging when vessels are nearby. The University of Victoria also joined in to take bursts of photographs that could be used to detect smaller boats. Seattle philanthropists contributed…
Read the full article here: https://www.opb.org/news/article/could-slower-ships-help-the-orcas/