Juvenile Pacific salmon face multiple challenges during migration
Dr. Andrea Frommel holding a juvenile chum salmon used in the lab experiment. Photo credit: Andrea Frommel
Despite the cultural and economic importance of Pacific salmon, populations across the Pacific Northwest have been in decline due to anthropogenic stressors, including overfishing and climate change. Climate change is driven in part by excess carbon dioxide emissions, much of which is absorbed by the ocean, a process known as ocean acidification. In dynamic coastal areas such as the Tidal Mixing Zone, where Pacific salmon migrate from the Fraser River to the Pacific Ocean, carbon dioxide levels can be highly variable.
Juvenile chum salmon already face several challenges during their migration to the ocean, including low availability of plankton in the Tidal Mixing Zone. While other juvenile fish, such as Atlantic herring and cod, appear to have greater tolerance to the effects of ocean acidification when food is plentiful, it’s unclear whether the same is true for Pacific salmon. A laboratory study conducted by researchers from the University of British Columbia set out to address this gap by investigating the individual and combined effects of carbon dioxide exposure and food deprivation on the survival and body condition of juvenile wild chum salmon.
Ocean acidification directly impacts survival of juvenile Pacific salmon
Contrary to what was expected, “we showed that the high vulnerability of juvenile chum salmon to ocean acidification persists with high food concentrations,” says Dr. Andrea Frommel, Assistant Professor at the University of British Columbia’s Department of Land and Food Systems, Adjunct faculty member at the Institute for the Oceans and Fisheries, and lead author. While food deprivation affected body condition and immune systems in juvenile chum salmon, ocean acidification alone directly led to “ionoregulatory failure” – meaning the loss of ability to maintain salt and water balance in an individual’s cells – and mortality regardless of the amount of food energy available to individuals.
Laboratory exposure experiments for juvenile chum salmon. Photo credit: Andrea Frommel
“This is surprising and alarming, as the common notion is that fish at this developmental stage should be able to regulate the respiratory acidosis resulting from these rather low levels of carbon dioxide. Turns out, small chum in particular, are not,” says Dr. Frommel. “It is likely that the stress associated with the transition from fresh to saltwater impairs their capacity to deal with the acidosis caused by the carbon dioxide.”
What these findings could mean for salmon farming and conservation
While chum salmon are not currently a farmed species, this study serves as a warning for salmon farms, especially those using open-net pens in coastal areas with naturally high carbon dioxide or land-based systems where levels can accumulate. “Few countries regulate carbon dioxide levels in aquaculture, and even Canada’s conservative limit of 10 mg/L exceeds the levels that proved lethal in this study,” explains Dr. Brian Hunt, co-author and Associate Professor at the Institute for the Oceans and Fisheries.
“Salmon Farm” by mlcastle is licensed under CC BY-SA 2.0.
Beyond aquaculture, these findings also have implications for the conservation of wild salmon. “One important takeaway is that not all salmon are equal,” Dr. Frommel explains. “To better manage and conserve Pacific salmon, we need to know species-specific and life stage–specific responses to environmental conditions and focus management efforts on the vulnerable stages that are potential bottlenecks to survival.” Given that carbon dioxide levels are already monitored in the region, the physiological thresholds identified in this study could be integrated into predictive models to improve salmon management and recovery planning in the future.
Sampling team involved with the laboratory exposure experiments for juvenile chum salmon. Photo credit: Andrea Frommel
The study, co-authored by Andrea Y. Frommel, Arash Akbarzadeh, Virginie Chalifoux, Tobi J. Ming, Brenna Collicutt, Kate Rolheiser, Rumer Opie, Kristina M. Miller, Colin J. Brauner, and Brian P. V. Hunt, was published in Ecological Applications, Volume 35, article number 5 (2025), under the title “High sensitivity to ocean acidification in wild out-migrating juvenile Pacific salmon is not impacted by feeding success.”
Tags: acidification, adjunct faculty, Andrea Frommel, aquaculture, Brian Hunt, faculty, fish farms, fishing farms, Pelagic Ecosystems Lab, Research, salmon, UBC Land and Food Systems