Killer whales have been shown to be affected by the noise from boats in their vicinity. The vessels' sounds harm the animals' ability to communicate with each other and to find food. Now it's been asserted that it's less the size of the boat causing the sounds than it is the speed at which it is moving.
That's the conclusion reached by new research out of the University of Washington (UW) and National Oceanic and Atmospheric Administration (NOAA) Fisheries, which studied boat noise as it reached Southern Resident killer whales (a Pacific Northwest community of orcas) in the inland waters of Washington and British Columbia.
Researchers say vessel traffic in those waters has quadrupled since the 1980s, the noise now affecting a Southern Resident population that stands at about 80.
The scientists temporarily attached special digital recorders to a group of whales, using suction cups to hold the devices in place (see photo above; they automatically detach within hours of placement). The recorders kept track of the amount of noise that reached the giant creatures as they swam amid commercial and residential vessels.
While the recorders captured the audio, a research boat nearby tracked the vessels using a special laser positioning tool, logging each boat by its vessel type, size, and location.
The new tools used in the study marked a departure from prior analyses.
While earlier studies logged the noise and counted the number of boats in the area, the new study was the first to examine the details of individual boats, along with accurate distances for each vessel from the animals.
Data from the ship-tagging system and the recorders in hand, the scientists were able to match ship factors with the noise that reached the whales.
"It definitely seems that speed is the most important predictor of the noise levels whales experience," said UW's Juliana Houghton, lead author of the research. She and her team suggest limiting vessel speed to protect the animals.
Currently, Washington state law prohibits vessels from coming within 200 yards of Southern Resident whales and requires them to maintain 400 yards clearance from any path the animals might take. But, speed-wise, there is only a recommendation not to exceed 7 knots within those 400 yards.
Houghton and her colleagues say the data they have captured should help NOAA Fisheries conduct an assessment over the next year of the effectiveness of those regulations.
The scientists' findings have just been published in the journal PLOS ONE.