[Cross-posted at Orcinus.]

Back when I was putting together a piece for Seattle magazine about the threats posed by increased shipping in orcas' territory to the endangered Southern Resident populatiom -- particularly the lethal specter of increased oil traffic -- I noted that one of the secondary threats posed by these large ships (including, possibly, coal ships coming from Cherry Point, north of Bellingham) is the terrific amount of racket they put up:

Along the western shore of San Juan Island, across Haro Strait, the view that most people observe when the killer whales are present is generally a placid one: The only noises are the sounds of the currents rushing, the “koosh” of the whales as they surface and blow plumes into the air—although at times, the calm is broken by the engines of the boats, sometimes 30 vessels at a time, that come crowding around the whales to get a close look at them. If there are large ships in view, they are mostly distant and seem almost silent as they glide past.

But drop a hydrophone into those same waters and the picture changes dramatically. There will be whales, all talking in their distinct Southern Resident dialect to each other and echolocating for fish. There will be the whale-watch boats, whose engines are mostly short-lived whines and low-level thrums. And then there will be large cargo ships. Because sound travels so well in water, a ship or a orca can be heard across great distances. The underwater sound of a loud ship passing a mile or two away produces a sound that compares to the sound a chainsaw might make in the air.

Val Veirs, a semi-retired physics professor, listens to all this racket, and monitors and records it with an array of hydrophones he has set up off his waterfront home on the west side of San Juan Island. What he and his fellow scientists have found is that killer whales will more often than not increase the volume of their vocalizations when there is higher background noise from boats and ships around them. Researchers at NOAA Fisheries are still studying whether whales fall completely silent because noisy ships are around.

But, according to Veirs, it’s inevitable that these noise levels—particularly the high-frequency component of ship noise—are going to affect their abilities to communicate and hunt, both of which are closely connected to sound. Vocalizations not only appear to play a role in the social component of their salmon-hunting behavior, the orcas also rely directly on echolocation.

Veirs says the ship-noise potential for all this traffic worries him when it comes to the whales. “Right now, about 60 percent of the time, there’s no ship within hearing range,” he says. “But if you put a couple thousand more ships per year in there, it seems to me you’ll end up with about 30 percent of the time...that the whales are able to communicate without interference from vessel noise.”

At the time I put the piece together, the conventional wisdom among whale scientists (including those at NOAA/NMFS, who I queried regarding the issue) was that whale-watching tour boats were a bigger problem for whales, because the frequencies of noise they created were more in the zone used by orcas and dolphins, whereas big ships created lower-frequency noise that was less likely to interfere.

Now, there is further research to corroborate Veirs' views:

Marla Holt, a research biologist with NOAA's Northwest Fisheries Science Center, has found that loud boat noise forces endangered orcas to raise the volume of their calls.

But the question, Holt says, is "so what? What are the biological consequences of them doing this?”

To answer that question, Holt and her NOAA colleague, Dawn Noren, a research fishery biologist, studied captive bottlenose dolphins.

They had the dolphin swim into a floating plastic helmet device and whistle at a normal level for two minutes. Then they rewarded the dolphin with fish. The device measured how much oxygen the dolphin used to accomplish that task.

Here's the dolphin whistling at a normal level (audio).

Then by knowing oxygen consumption, the scientists calculated the metabolic rate of the dolphin while making calls at a comfortable level.

Next, they had the dolphin whistle more loudly for two minutes (audio).

Holt and Noren found that when the dolphin was whistling harder and louder its metabolic rate rose by up to 80 percent above normal resting levels.

Just like with humans, when marine mammals' metabolism goes up, they burn more calories. Dawn Noren calculates that a dolphin making the louder call for two minutes would burn the same amount of calories it would get from eating half of a small fish.

These studies mainly looked at vocalizations, which appear to be the main way that orcas communicate. But even more important is the effect on their echolocation sense, which is fundamental to their ability to hunt prey. As Veirs explained it to me, some of this is just the sheer physics involved: When the volume of noise is that high, the amount of loss in the signal return from an echolocation click can be enough to render their ability to see underwater almost useless.

The studies also did not distinguish between noise from whale-watching boats and from large freighters. But what Veirs told me was that while the whale-boat noise could be intense, and it made a significant contribution to the problem, the biggest and most constant contributor to background noise, by far, was large shipping vessels.

My own experience corroborated what Val Veirs was saying. I own a hydrophone (thank you, Cetacean Research Technology) that I take kayaking with me, and I drop it in whenever whales are present (and sometimes even when they are not, just to see if I can catch any sound of them from a distance), and I've been using it for a number of years. That experience has made it clear to me that large vessel noise is far, far more likely to disrupt and disturb orca communication. After awhile you have to take the headphones off for some ships because they throw up such a racket.

[You don't need to go out in a kayak to experience this for yourself. You can listen to the stationary hydrophones at Veirs' observatory overlooking Haro Strait at the Orcasound link here -- or to the Lime Kiln Lighthouse hydrophone at the same website. Even if it's quiet when you start it up, leave it on for awhile and a ship will come by.]

It seemed obvious to me that the sheer volume issue alone was going to interfere with orcas' abilities to get clear signals back from their echolocation clicks. The volume of large-vessel noise was much more intense, and much, much more sustained.

And indeed, I have heard orcas shut up when big ships were present, and start vocalizing again when their noise went away. An example of this occurred the same summer I was out gathering some of the material for the Seattle article, and I described it there:

In calm seas off the west side of San Juan Island, my kayak bobs gently in a kelp bed. In the water about a quarter-mile distance from me, orcas mill and frolic, most likely hunting their favorite chinook salmon. I drop my hydrophone (an underwater microphone) into the water to listen to their distinct calls.

A low clanging—whang, whang, whang—fills my headphones. It is the steady and overpowering sound of a cargo ship, one of the regular features of underwater life in the San Juan Islands’ Haro Strait.

At first, a quick scan of the horizon doesn’t reveal the source of the noise. Finally, I spot it: A lone log-bearing ship heads out to the open sea around the very southern tip of Vancouver Island. Whang, whang, whang. It is at least nine miles away.

Finally, the ship rounds the bend, and the sea quiets for just a moment before the orcas’ distinct whistles, grunts and rat-a-tat-tat-tats fill the water. These are J pod whales from the Salish Sea’s famous and endangered Southern Resident orcas, and they are making the well-known calls known as “S1.”

Seemingly energized, the whales head toward my kelp bed and surround it, chatting loudly and rolling in the kelp. It crackles and pops underwater as the orcas rip up fronds while “kelping” themselves, something the Southern Residents are fond of doing, apparently for the massaging effect.

I recorded the whole event, which I've embedded below. This is the whole 24-minute recording. Now, I recommend using this file non-passively: trust me, you will want to skip over the clanging ship noise, which dominates the first five minutes. But I've included it here so you can get a sense of what I'm talking about regarding the incessant and pervasive quality of the noise from big ships. Once you get a taste of that, skip forward to about the 5:00 mark and you'll hear the orcas -- which had been milling off a rocky point, well within my view but not uttering a peep the whole time -- chirp up as soon as the ship noise fades away.

One of the fun things about this encounter was that I was indeed in a kelp bed, so when the orcas came by, I was well out of their way (you can hear me making some ungodly noise in a few spots on the recording as I repositioned myself into the middle of the kelp). What I also didn't realize is the amount of tearing and breaking of the kelp fronds that occurs when orcas "kelp" themselves, as they were doing here. That's all the crackling and popping you hear amid the vocalizations.

Here's a somewhat more pleasant version, with the extraneous ship noise and some of the silent spaces and paddling/repositioning noises edited out. This is the one you want to just hit "play" on:

The larger and more significant takeaway from this is that scientists should probably take a longer look at the effects of large ship noise, and begin thinking about ways to mediate that. Considering the amount of money that we're seeing go up and down Haro Strait, we have to know that making any changes there is going to be an uphill battle. But it may prove to be an important component of recovering this endangered population.