Every summer, thousands of visitors gather to watch rainbow trout, silver salmon, red salmon and Chinook salmon bravely jump up the fish ladder as they travel from Puget Sound to Lake Washington and spawning grounds further afield. So, there are also some hungry seals and sea lions.
"Pinnipeds — seals and sea lions — are much smarter than I think we think," said Laura Bogaard, an ecologist at the Oceans Initiative, a Seattle-based nonprofit research organization. "They found out it was a buffet."
For decades, pinnipeds have congregated at the Ballard Locks to devour fish stocks that have been under pressure from pollution, habitat loss and overfishing. To protect these fish, conservation managers have been trying various methods to drive them away. They installed a fiberglass killer whale that makes predatory calls and uses a device called a pinger to try to scare off the pinnipeds. (Pinger turns out to be more of a bell-ringing effect.) They even fed the pinnipeds lithium chloride, a toxic but not lethal chemical, and continued to use firecracker-style seal bombs.
None of the methods they've tried seem to work. The problem is so long-standing that some conservation managers advocate extreme measures like culling problematic pinnipeds.
"The biggest challenge," says Andrew Trites, a pinfoot researcher at the University of British Columbia, "is that you're trying to prevent [pinnipeds] from doing something [with] such a positive reward, which is eating." Food is the ultimate reward, which is why stopping is almost impossible. ”
But Bogaard says a new device called Target Acoustic Shock Technology (TAST) appears to be working in cases where other approaches have failed.
Between 2020 and 2022, Bogaard tested TAST at the Ballard Locks. She found that while the number of seals in the area remained the same, they were farther away from the fish bodies. However, the project was closed in the summer of 2022 because the protocol was incompatible with other management measures used at the Ballard Locks. Bogaard plans to continue testing the device at Tumwater Falls Park, another salmon block in Washington.
Thomas Götz, a marine mammal researcher at the University of St Andrews in Scotland and co-created the technique, said TAST represents an exciting new advance in flipper deterrence because it utilizes something called acoustic shock reflex. "If sound has certain properties, then it triggers muscle contraction — retreat," he said. For pinnipeds, he explained, noise is like nails on a blackboard.
After years of studying the effects of sound on marine mammals, Götz, along with TAST's lead developer Vincent Janik, also at the University of St Andrews, found that sounds ranging in frequencies between 500 and 2,000 hertz startled seals, but were largely beyond the sensitive hearing range of other wild animals such as salmon and whales. They also found that, unlike existing acoustic deterrent devices, such as pingers, to which pinnipeds eventually become accustomed, TAST's particularly harsh noise produces a flight response that appears to become stronger with repetition.
In Götz's experiments at Scottish fish farms, the use of TAST led to a 97% reduction in the predation rate of pinniped fish. The technology is currently being used in fish farms in Scotland and Norway, and Götz is studying its potential to stop finnipeds and whales from using nets and oil spills.
Trites, who was not involved in the study, said TAST has exciting potential. "It's a beautiful concept, but I think it still needs further testing and validation to make sure it does work." The environment and specific location in which the device is used could be important nuances of its effectiveness, he said.
Bogaard is also cautiously optimistic about the technology, but she is careful to point out that this is not a panacea to save endangered fish.
"I think, combined with other management practices, it definitely shows a lot of promise in terms of its ability to keep seals away from specific areas of concern," she said. But if the ultimate goal is to save salmon, she added, more work needs to be done to protect the watershed where salmon spawn.