Transboundary Salish Sea study finds answers to why wild salmon are dying
For millennia, the Salish Sea – the shared body of water connecting southern British Columbia and northwestern Washington State and encompassing Puget Sound, Juan de Fuca Strait, and the Strait of Georgia – was abundant in salmon.
The key species is the foundation of the entire Pacific Northwest ecosystem. The seven species of Pacific salmon populated the Salish Sea, supporting a host of other iconic animals, such as bald eagles, southern resident killer whales, and grizzly bears, as well as their surrounding aquatic and terrestrial environments and numerous indigenous nations and cultures.
But, from the late 1970s, salmon survival, especially chinook, coho, and rainbow trout – which migrate to the ocean like salmon, but can spawn multiple times – a started a mysterious decline, especially in the marine environment, said Isobel Pearsall, director of marine science at Vancouver’s Pacific Salmon Foundation (PSF).
Some populations in Salish waters have dropped as much as 90 percent, and limiting fishing, restoring habitat and improving hatchery practices didn’t make any significant differences, Pearsall said.
It is clear that juvenile fish are particularly vulnerable and that there is something peculiar about the Salish Sea that impacts the survival of the three species, which do not face the same pattern of decline in others. regions, she said.
In partnership with Long Live the Kings, another non-profit foundation south of the border, PSF launched a five-year research initiative involving 60 entities to understand what drove certain salmon stocks to extinction and what that could be done to reverse it, she said. .
Despite the dire situation facing salmon, the key findings from the recently completed Salish Sea Marine Survival Project can serve as a roadmap for priority actions, research and policy, said Pearsall, coordinator of the ‘initiative.
“It’s very easy to get caught up in the pessimism of what we’re seeing around the decline of salmon,” Pearsall said. “But the [survival project] highlighted the areas we really want to focus on and which we know are crucial.
The study found that the Salish Sea is undergoing significant changes due to the climate crisis, such as warming waters, increased risk of algae and harmful pathogens, changes in the marine food web and decimation of fish. estuary and foreshore habitats. Many of the changes affecting salmon are intertwined, Pearsall said.
“One would hope for a smoking gun and there would be one major thing you could change to solve the whole problem, but that doesn’t appear to be the case,” she said.
However, the initiative concluded that the salmon food supply and predation by juvenile salmon are two key factors in the decline of chinook, coho, and rainbow trout when they first enter. in the marine environment.
The Salish Sea Marine Survival Project has identified the main stressors causing the decline of juvenile salmon.
Changes in the Salish Sea affect when, where and how much food is available to juvenile chinook and coho salmon, affecting their growth and mortality.
Declines in zooplankton and forage fish, especially herring, put young salmon at increased risk, a situation exacerbated by destruction of estuaries and coastal habitat, which provide hiding places and food for fish and fish. their prey.
The finding suggests that protecting and restoring estuarine and forage fish habitat on coastal tidal flats should be a priority, Pearsall said.
In addition, it is important to redouble our efforts to stimulate the decline of herring populations and to study their distribution and movements.
Young salmon are also under pressure from increasing numbers of harbor seals in the Salish Sea, according to the project.
Although chinook salmon and coho make up a limited portion of the seal diet, the number of seals negatively impacts the survival rates of salmon, already strained by human-made climate change, said Pearsall.
The study does not advocate widespread culling, which would require the elimination of up to 50 percent of the seal population, and the constant elimination of a significant proportion each year thereafter, to have any real effect. on salmon, she said.
“It is simply untenable to make such a drastic move in an ecosystem that no one fully understands,” said Pearsall. Other pressures and changes are also at play as abundant salmon stocks have existed alongside large seal populations in the past, she added.
“I think we need to look at the anthropogenic changes we’ve made that make salmon more vulnerable to predation.”
This could include removing infrastructure such as booms in estuaries where seals can wait for salmon without fear of being eaten themselves. Or by changing hatchery practices, such as releasing large groups of juvenile fish upstream, often at low tide, which makes it easier to collect young salmon for creatures such as raccoons and herons.
Implementing solutions that could ensure higher river or stream flows to provide more cover and cooler water to young salmon would give them a chance to fight predators and increase their survival, Pearsall said. . The holistic and collaborative nature of the Salish Sea Project has enabled stakeholders on both sides of the border to respond more effectively and in a coordinated manner to achieve gains in restoring endangered salmon stocks, a- she declared.
While the study fits the spectrum of pressures on salmon, it also highlighted some practical actions, Pearsall said.
“We let people know that what they are doing can have impacts, both negative and positive.
“Some things may be out of our control, but there are many immediate actions that we can take. “