When the ocean changes the rules for Wild Salmon

Canada’s wild salmon are more than a symbol. They are food, culture, livelihoods, and an ecological thread tying rivers to the ocean and back again. Canada’s Wild Salmon Policy (WSP) was designed to protect that thread through conservation, habitat protection, and long-term management. However, the ocean side of the story is changing fast. A study by UBC Institute for the Oceans and Fisheries researchers Dr. Jacob Lerner, Dr. Anna McLaskey, and Dr. Brian Hunt argues that rapid ocean change is testing whether policy and management can keep up when new threats appear.

One of those threats has a deceptively gentle name: thiamine deficiency complex. Thiamine is vitamin B1, a nutrient essential to fish health. Salmon build thiamine stores at sea through what they eat. Those stores help adults endure migration and are passed from mothers into eggs, supporting fry in the earliest, most fragile stage of life. When thiamine in eggs drops too low, survival can collapse. In severe cases, fry mortality can exceed 90%. As the authors put it, “Low levels can lead to high incidence of fry mortality (> 90%).” The scary part is that the problem can be hidden: adult returns may look normal, while the next generation quietly fails.

Thiamine deficiency is not a single-cause issue. It is an ecosystem signal that can emerge when the food web shifts. Thiamine begins at the base of the food web, produced by certain phytoplankton and bacteria, then moves upward through prey and into salmon. But some prey contain thiaminase, an enzyme that breaks down thiamine and blocks absorption. Thiamine and thiaminase levels vary among prey species and can change over time. Warming and ocean stratification can also reshape surface waters in ways that may reduce thiamine supply. The result is a nutritional trap: salmon may still find prey, but the diet may deliver fewer of the nutrients needed for reproduction and early survival.

For years, thiamine deficiency was not widely recognized as a major Pacific salmon concern. That assumption has shifted as the issue has been detected in Pacific salmon systems outside Canada, including cases linked to low egg thiamine and high fry mortality. What stands out is how quickly it can appear, suggesting it may be triggered by sudden ecosystem reorganization.

In British Columbia, the study notes that a major assessment effort has recently started to examine Chinook egg thiamine. Early signals suggest that in some ecologically distinct populations, a variable and sometimes large share of females can have egg thiamine concentrations associated with thiamine deficiency complex. That uneven risk makes it difficult to manage with a single, uniform approach.

There are ways to respond, at least in the short term. In hatchery contexts, thiamine-enriched egg baths or injections for pre-spawning females can help reduce early mortality, and some treatments are already being used. However, these measures do not solve the bigger question: what is changing in the ocean, and why is the food web failing to deliver what salmon needs?

This is where the research connects back to policy. The WSP has built important foundations, including conservation planning and monitoring structures, and it recognizes the importance of ecosystem information. Still, the authors argue that fast-moving ocean change creates a new reality where subtle threats can appear quickly and outpace traditional monitoring. Counting fish and tracking broad trends remain essential, but they may miss the underlying drivers, as in the case of thiamine deficiency where the problem is nutritional, not simply abundance. As the paper warns, “WSP’s emphasis on long term monitoring programs may tether it to established ecosystem indicators and may lead to managers missing emerging effects on salmon.”

Thiamine deficiency, in that sense, becomes a stress test for modern salmon management. Meeting it requires mechanistic ecosystem research that links climate conditions, prey communities, and salmon health, and turns those links into practical decision support. It also requires collaboration across regions, since salmon and ocean processes do not follow borders and warning signs may appear elsewhere first.

The main message is not that the Wild Salmon Policy has failed. It is that the ocean is changing the rules, and management needs the speed and flexibility to respond. Thiamine deficiency shows how an invisible shift at the base of the food web can echo forward into the next generation. An important factor in enabling TDC research in BC to get off the ground quickly and include investigations of ecosystem drivers in addition to monitoring was a unique source of funding through the BCSRIF, which comes to an end in 2026. Protecting wild salmon in the years ahead will depend on detecting emerging threats early, understanding their causes, and acting before quiet losses become irreversible.

Changing oceans, ecosystem effects, and Canada’s Wild Salmon Policy, was published in the Canadian Journal of Fisheries and Aquatic Sciences.

Tags: Anna McLaskey, biology, Brian Hunt, Chinook salmon, climate change, coastal ecosystems, ecosystems, faculty, fisheries management, IOF postdoctoral fellows, IOF Research Associates, Jacob Lerner, marine ecosystems, Pelagic Ecosystems Lab, plankton, Research, salmon, thiamine