Sea level rise could squeeze young salmon out of places to live
‘Future-proofing’ habitat on Vancouver Island means mapping out estuaries and protecting land onshore
In Parksville, B.C. on Vancouver Island, Phoebe Gross leads a small group over a muddy flat at the mouth of Englishman River to capture juvenile salmon and gather information about where they live.
"Right now we're going to one of the marsh sites," said Gross, a master's student at Simon Fraser University's Salmon Watersheds Lab.
The area Gross is in will be submerged at high tide, but for now when the water is low, she can access an offshoot of the Englishman River that flows into the Pacific Ocean.
She and her colleagues at the Salmon Watersheds Lab, in partnership with several First Nations and the Nature Trust of British Columbia, are studying eight estuaries on Vancouver Island — important habitat for young salmon before they're ready to survive in the open ocean.
This will help the researchers create a model mapping out how global warming is likely to alter those sites in the coming decades, and can inform how to best protect young salmon not just today, but into the future.
If urgent action is taken to reduce greenhouse gas emissions, sea levels are expected to rise some 40 cm by the end of the century; if that doesn't happen, much worse damage is projected — rising nearly a metre.
Juvenile salmon already face pressure from human land use and development, and may be further squeezed out of their estuary habitat by climate change, as sea levels rise.
Rising seas mean salmon nurseries are on the move
Climate change is altering oceans around the world, including the Pacific.
"Sea level rise is going to drive shifts in a number of really important things for salmon," said Gross.
Estuaries are considered nursery habitat for salmon, with the right temperatures and a mix of salt and fresh water they need as they grow, before migrating to the ocean.
As sea level rises, that habitat sweet spot will, in theory, shift up too: as brackish water moves on land, estuary plants will also move further inland.
However, this requires surrounding habitat to be intact.
Since colonization of the area, development and industry have altered the Englishman River Estuary, traditional territory of the Nanoose First Nation, a partner in the Salmon Watersheds Lab research.
"The reason our village was there is because it was right beside … the Englishman River," said Nanoose First Nation Councillor Chris Bob, who collaborates with the SFU researchers in the field.
Dog — or chum — salmon from the Englishman "got our people through the winters," he said. "We would smoke that fish, we would store that fish, we would trade that fish, but it would provide for us through … all those generations, all those thousands of years."
In the 150 years since the formation of Canada, Bob has seen the fishing industry "nosedive."
"Our wealth is being damaged and taken away … but the thing is we do the best we can to protect what we have left and we try to ensure that resource is going to be there for our future generations, that's our responsibility."
One aim of the collaborative research is to provide data to inform management decisions for Pacific salmon, in an effort to keep the important cultural, ecological and economic species healthy on Vancouver Island as the climate changes.
Planning for 'coastal squeeze'
Of all the eight locations Gross and her colleagues are studying on the Island, the Englishman River Estuary is the most heavily altered by human use and development. It's flanked by an RV resort on one side and a man-made spit of land on the other side where an art gallery once stood. That land is now being restored as part of the estuary to improve the natural flow of tidal water.
"We have all of these houses on one side and this trailer park on the other side. So if they're there and they're not moving and the estuary is moving in, the estuary has nowhere to go and it'll eventually get drowned out," said Gross, explaining that the water would become too deep for estuary plants to grow, compromising the habitat that juvenile salmon need.
"That's a process that's referred to as coastal squeeze," she said.
"Coastal squeeze is a huge factor for estuaries like the Englishman," said Steve Henstra, a restoration biologist with the Nature Trust of British Columbia's West Coast Conservation Land Management Program.
"It's quite significant when you have an area of very flat relief, like an estuary, you can picture what if the sea level is a metre higher. It's going to be over top of a lot of it. So it has serious implications for estuaries," said Henstra.
As part of restoration in the Englishman River Estuary, the Nature Trust of British Columbia has removed a berm constructed in the 1960s to access a log-booming area at the Englishman River. This allows the flow of tidal water back in, which creates the conditions estuary plants thrive in.
Restoration includes other actions, like planting estuary greenery, providing large, dead trees which small salmon use as protection from predators, and also dismantling built-up shorelines. However, Henstra says understanding where estuary habitat will be as seas rise is a critical step in making decisions that won't only benefit salmon today, but for decades into the future.
"With our limited amount of funds and effort, are we investing in something that … is going to exist in 100 years with sea level rise and climate change," Henstra asks himself about the land acquired by the Nature Trust of British Columbia.
"Your dollars are better spent like future proofing that estuary so to speak where you're focusing on adjacent upland land acquisition," he said.
One of the goals of the Salmon Watersheds Lab's research is to see where the estuary habitat will be "so that we can proactively inform either restoration or conservation" to keep habitat for salmon around into the future, said Gross.
"With these projections we can actually test out specific restoration actions," said Gross.
For example, by replanting vegetation in one part of an estuary, "how might that change future salmon habitat, or if we remove this culvert would that open up more habitat for salmon?" she said.
The research is paid for by a restoration fund, supported by both the federal government's Department of Fisheries and Oceans and the province of British Columbia.
The B.C. government has spent $57 million over the last two years restoring watersheds and river systems, including salmon habitats, said a spokesperson with B.C.'s Ministry of Water, Land and Resource Stewardship and Fisheries by email.
In its 2023-2024 Southern BC Salmon Integrated Fisheries Management Plan, DFO notes that in B.C., "we do not anticipate that long-term salmon survival patterns will return to what we have seen historically. Pacific salmon are already responding to environmental changes driven by climate change and other human activities."
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