Seals love devouring salmon at Ballard Locks. One way to stop them: Tail-slapping noises
For decades, humans have been trying different ways to keep seals and sea lions away from the Ballard Locks' fish ladder. Now, scientists are trying a new method to outsmart the seals.
Laura Bogaard was hanging out on the south side of the Locks when a seal popped its head out of the water.
“Aren’t they adorable?” Bogaard asked in the cooing tone usually reserved for babies. She made a t-t-t-t-t sound, and the seal turned its head to look at her. “They’ll look at you if you kind of make a noise at them,” she said.
Bogaard is a scientist with the non-profit Oceans Initiative. She knows how to interact with seals because she spent about a month, from mid-August through mid-September, perched on a platform at the southwest corner of the Locks, watching them.
And this seal was watching her.
“He’s been kind of watching me all day,” she said. “They’re probably wondering why I’m not on the platform today, I do believe. I mean, they’re so smart.”
The seals have learned where Laura Bogaard usually is. They’ve also learned where the salmon usually are.
And that’s an issue, because these slippery pinnipeds are hard to outwit.
If you’re a seal, the Ballard Locks are a great place to find a snack. Seals eat a lot of salmon as they migrate through the Locks’ fish ladder to try to reach spawning grounds on the other side. Some of those salmon are Chinook, the only food of the starving Southern Resident orcas.
For decades, humans have been trying different ways to keep seals and sea lions away from the salmon at the Locks’ fish ladder. Now, scientists are trying a new method to outsmart the seals.
Where the Ballard Locks are, there used to be a stream between Lake Washington and Puget Sound. Now, there’s a ship canal, along with what one of Bogaard’s friends "lovingly refers to as a boat elevator," Bogaard said.
Migrating salmon can’t go through the boat elevator, and they can’t swim up the spillways where the water is fast-moving and white-capping. They can only navigate the fish ladder, which is just a few feet wide. It's on the south side of the Locks, opposite where the boats go through.
That’s where seals go to pick them off.
Because of this predation — along with other factors like pollution and habitat destruction, “Those runs are slowing down,” Bogaard said. “They’re seeing fewer and fewer numbers come back every single year.”
Bogaard grew up in Seattle and remembers visiting the Locks in elementary school.
“And I feel like every Seattle kid has had that experience of going with their first, second, third grade class to the Locks and learning about ecology,” Bogaard said. “And it’s kind of our responsibility to try anything we can to make sure that our kids and our grandkids can have that same experience.”
That’s why Bogaard spent a month watching the seals. She wanted to know how they responded to a new device designed to startle them away from the fish ladder.
It’s a device that makes the sound of a tail slapping the water, which the seals seem to mistake for a predator coming to eat them.
“It sounds like kshhhhh, kind of like static,” Bogaard said.
In the past, scientists and others have tried to get seals and sea lions away from the Ballard Locks and other migratory pinch points like dams by throwing firecrackers into the water, trapping the animals and relocating them, and playing loud noises.
None of that worked very well.
“One of the things that was learned decades ago was that the animals that are used to being there and finding fish were more resistant to the acoustic deterrents,” said Lynne Barre, a marine biologist for the National Oceanic and Atmospheric Administration.
Sometimes, sound devices that were supposed to scare seals away even had a dinner bell effect, alerting them to the presence of prey and attracting even more of them.
“One of my colleagues told me the story of the sea lions or the seals swimming with their head above water so they weren’t hearing the noise and it wasn’t annoying,” Barre said, “until they got really close to the fish ladder and then just diving down to catch the fish.”
But Laura Bogaard said this device is different because it tries to evoke a startle response instead of just irritating the seals with a painfully loud but continuous or predictable noise.
The noise comes randomly, so the seals can’t get used to the schedule. It’s also species-specific; it doesn’t work on sea lions. And it’s quite loud.
To see how well this was working, Bogaard stood on the platform and recorded how many seals she saw, where she saw them, and what they were doing.
“When I do catch them with a fish in their mouth, they totally get — you know when dogs have done something wrong and they kind of give you that, like, side-eye of, like, ‘I don’t know what you’re going to do, but I know I didn’t do something right’?” Bogaard said. The seals “definitely kind of freeze and look at you, like ‘drop the fish.’”
Bogaard said, after a month of watching the seals, her sense was that the device was effective.
“The seals do spend more time further away [from the fish ladder] when the device is on,” she said. “I’m hopeful that I’ll see that reflected in the data as well.”
This device can't work everywhere. At dams along the Columbia River, for example, the background noise is too loud for any acoustic device to be effective; seals and sea lions simply can't hear anything above the din. But, if this new device works at the Locks, the plan is to use it there while salmon are migrating, and at other pinch points like salmon hatcheries as well.