Ocean Acidification and the Future of Salmon

­Salmon are important species, not only to humans but also to the natural world. They provide sustenance and economic resources for us, and within their ecosystems, they’re a keystone species—a vital connection in the food web, playing a critical role in their environment.

So what will happen to these vital fish as our planet changes? Effects of ocean acidification appear to be limited for fish in the sea, especially compared to shellfish, but what about in freshwater, where salmon begin and end their lives? How do rising carbon dioxide (CO₂) emissions affect fish in lakes, rivers, and streams?

Michelle Ou of the University of British Columbia and her colleagues wanted to answer this question. To do so, they set up experiments in their lab, using the important and wide-ranging pink salmon (Oncorhynchus gorbuscha) as their test subjects.

These salmon, like other salmon species, begin their lives in freshwater streams. The fish start out very tiny, spending their first few months close to home. They then head out to the ocean while they are still small, adapting to the sea water as they grow significantly larger. Two years later, they return to the stream where they hatched to spawn and die.

Ou wanted to understand the effects of acidification on these innate salmon behaviors. To do this, she reared pink salmon embryos and juveniles for 10 weeks, in two separate tanks—one with current CO₂ levels, and the other at the elevated CO₂ levels predicted in the future. The team discovered that the hatchlings and juveniles exposed to higher levels of CO₂ were significantly smaller than those raised at today’s levels. Smaller fish are at higher risk of predation in streams and as they enter the ocean.

To make matters worse, the olfactory sense of the salmon seemed to be impaired at higher CO₂ levels, making the fish less likely to respond to the proximity of a predator, putting them in further danger.

If we don’t do something to stop future CO₂ emissions, the team writes in Nature Climate Change, “populations of pink salmon may be at risk.” In an accompanying News & Views article, scientist Philip Munday states that the fish do have a chance of adapting to more acidic waters: “One positive for pink salmon is that they have very large populations, they are highly fecund, and they complete their lifecycle in just two years. Consequently, there is likely to be genetic variation within existing populations that could assist them in adapting to future high CO₂ levels.”

Let’s hope (and help ensure that) this important fish is around for many years to come!

Image: E. Peter Steenstra / USFW / Flickr