Over the past 50 years, local populations of seals and sea lions have grown steadily while feasting on threatened and endangered runs of steelhead and salmon. Those fish populations, meanwhile, have continued to lose ground.
This predation problem is well-known in the mouth of the Columbia River. Lesser-known is its impact at several sites around Puget Sound and the Hood Canal. A new coalition of Washington state and federal wildlife officials and tribes, supported by the nonprofit Long Live the Kings, is wrapping up a year-long effort to learn more.
Called the “Pinniped Predation on Salmonids” project, the intensive investigation is taking a novel approach, according to Casey Clark, the state’s lead marine mammal researcher. Scientists deploy drones in key locations to get aerial photos of seals. Those photos, combined with thumb-sized tags on the seals’ hind flippers, allow scientists to get more accurate counts of the seals and the best estimates of local populations to date.
“That's part one. It was a lot of work to get to part one,” Clark said. "But once we know how many seals there are, you have to know what they're eating. And that has meant a whole lot of seal poop scooping, a whole lot of scat collections.”
The team examined the contents of the samples and measured certain bones to determine the size and age of fish the seals had eaten. They’re also doing DNA analysis of the scat.
Clarke said he expects to have results from computer modeling by the end of 2026. The information will be used to advise on policy decisions for things such as habitat restoration and infrastructure design. The aim is to reduce predation and improve ecosystem management.
The project is focused on pinch points that have become predation hot spots, but haven't been in the spotlight — places like the Hood Canal Bridge, the Nisqually Estuary and the Duckabush River on the Olympic Peninsula, where seals haul out and enjoy easy feeding on endangered salmon and threatened steelhead trout.
Prior studies indicate that harbor seals consume between 9% and 33% of juvenile steelhead in the Nisqually River, but regulators say they need to know more about the problem in order to address it appropriately.
Tribes say the lack of sustainable salmon harvests is undermining their treaty rights.
“The tribes as well as the state and federal government -— we've put a tremendous amount of money into recovering salmon. Decades of effort and resources have gone into restoring habitat,” said Hans Daubenberger, a senior research scientist with the Port Gamble S’Klallam Tribe.
Daubenberger pointed out that the state’s Hood Canal Bridge traps millions of juvenile salmon every year.
“You end up with literally millions of fish stacked up against the bridge when you're out there during the spring migration,” he said. “It looks like, if you've ever been to a hatchery raceway, like unreal numbers of fish.”
Daubenberger said the seals have gotten good at corralling the fish into tight schools that they then swim through and eat from. Preliminary estimates place the mortality rate of smolts at the Hood Canal Bridge as high as 50%.
The project is also exploring the effectiveness of underwater acoustic deterrence to reduce the seals’ predation at the bridge — that is, using noise to startle them. In the long term, the researchers hope to keep working with the state to develop habitat restoration projects and bridges that will prevent pinniped predation.
These efforts face funding challenges, with current support from federal grants recently slashed and tribal partnerships struggling to keep up.
