The knock-on effects of cumulative threats to salmonids has Simon Fraser University researchers pushing for more effective strategies to protect British Columbia's most important fish populations.
Salmonids which include salmon, trout, charr and grayling are vital to communities and ecosystems such as those of the West Coast, yet little is known about how these species will respond as the stressors they face compound an increasingly likely scenario under climate change.
A recent SFU-led study published in Environmental Management is the first to quantify the cumulative effects and interactions of multiple stressors on these species.
Pedro González-Espinosa, a postdoctoral fellow in SFU's Ocean Equity Lab and lead author of the paper, explains that these species are sensitive to a range of environmental stressors including water quality, temperature, pollution and more.
"Understanding whether these stressors accumulate and how they interact may help to implement conservation and management efforts more effectively and predict salmonid responses to environmental changes, particularly those driven by climate change and human activities," says González-Espinosa.
The study, which looked at interactions between stressors and various salmonids across dozens of existing studies, classified interactions as being either additive, synergistic or antagonistic.
The findings revealed that half of the interactions between multiple stressors were additive, where the combined effect was equal to the sum of their individual effects. Over 30 per cent of interactions were synergistic, meaning the combined effect is greater than the sum of the stressor's individual effects, amplifying each other's negative impacts. Finally, less than 20 per cent of interactions were antagonistic, where the combined effect of the stressors is less than the sum of their individual effects.
For example, if temperature and pesticides both negatively affect salmonids, their combined effect might be more harmful than just adding their individual impacts, potentially due to factors like increased toxicity of pesticides at higher temperatures. On the other hand, in some cases, temperature changes might reduce the negative impact of invasive species on salmonids by altering their behaviour or causing them to find refuges in cooler areas, which helps mitigate the competitive pressure from the invasive species.
The study also revealed that the most frequent combination of stressors across all paired interactions was temperature with pesticides and temperature with metals. In the case of pesticides, given their widespread use in agriculture and the ongoing impacts of global warming, this occurrence of stressors is commonly observed. Similarly, metals like copper, zinc, and lead often come from industries, mining, and agricultural runoff. Just as occurs with pesticides, warmer temperatures can make the toxicity of these metals more harmful to fish.
"The fact that most interactions are additive or synergistic means that salmonids may be more vulnerable to environmental pressures than previously thought, especially when multiple stressors co-occur," González-Espinosa explains.
Understanding the cumulative effects of these stressors and their interactions is key to informing future management and conservation decisions, and can pave the way to more effective climate adaptation strategies for salmonids.
For example, González-Espinosa notes that shifting conservation and policy efforts to prioritize areas where multiple stressors co-occur to produce an additive or synergistic effect, like a polluted stream experiencing warming temperatures, could reduce the overall impact on these species.
"By identifying key stressor interactions, this research lays the groundwork for more effective management strategies, particularly in the context of climate change and human activities. This helps identify which stressor combinations are likely riskier, allowing for more targeted conservation efforts," he says. "Better knowledge allows for more targeted and effective management strategies to protect salmonid populations and also the coastal human communities that rely on them."
