A Canadian frigate used its mid-frequency active sonar this week during a training exercise in Haro Strait, north of San Juan Island and south of Vancouver Island.  The sonar emissions from the HMCS Ottowa (right) were picked up by whale researchers at Beam Institute, who raised concerns about sonar use in an area designated by the US as critical habitat for orcas. You can read a detailed report from Beam, including sonograms and MP3 files of the sounds heard, at their website. They note that “the peak power frequency is consistent with the 2-8 kHz frequency range specified for the SQS 510 sonar system, which is manufactured by General Dynamics Canada. Each ping had high intensity receive levels for ~0.5 second duration and pings were separated by about one minute.”

According to the Seattle Times:

The frigate was in Canadian waters at the time, said Lt. Diane Larose of the Canadian navy.  But the Ottawa’s sonar can travel 4,000 yards — more than two miles — and the sound was picked up by instruments in U.S. waters. Larose said the Canadians are well aware of sonar’s potential to hurt killer whales, which communicate by sound at similar frequencies. In 2008, the Canadian Navy adopted a policy requiring the use of radar, passive acoustic systems, underwater listening devices and night-vision goggles to make sure marine mammals aren’t present when sonar is deployed. “We take this very seriously,” Larose said. “It’s a very well-thought-out policy.”

Scott Veirs of Beam Research said that their monitoring network had tracked both transient orcas and endangered southern resident orcas in the area within 24 hours both before and after the incident. “This was a fairly high-risk event as far as we can tell…it’s concerning to me that the U.S. Navy has voluntarily refrained from unnecessary testing and training in the inland waters of Washington state, but the Canadian navy apparently still does,” he said. “The nightmare scenario is that you turn on sonar not knowing they are there and essentially deafen them either temporarily or permanently.”  Ed. note: Beyond this worst-case scenario, the use of this high-intensity sonar in waters close to designated critical habitat goes against the purposes of designating such protected zones; the US has banned all boat activity in some parts of the habitat, with the goal of assuring that the whales are not discouraged from using this region, one of their primary feeding grounds.

Interestingly, a commenter on the Beam Reach website notes that the Canadian Navy’s safety zone for their mid-frequency active sonar is 4000 yards, or over two miles.  Whether they can effectively detect whales at that distance, especially at night, is highly questionable. The Seattle Times clip above mistakenly presumes that the sounds travel only that far. In fact, this is just where they tend to drop below the sound levels considered likely to seriously disrupt behavior; mid-frequency active sonar can be heard for tens of miles, and in the complex underwater landscape of where this event took place, is likely to create dramatic peaks and drops in sound levels as the noise bounces from islands and the seabed, making it difficult for animals to know how to reduce their exposures.