Notre Dame graduate student Peter Levi takes a break from his research on Pacific salmon to tell us about their impacts as well as the impacts of their Atlantic brethren.
Atlantic salmon (Salmo salar) are a popular dinner item from coast-to-coast. But the number of these fish in the Pacific Ocean may soon outnumber those in the Atlantic Ocean! That may sound preposterous…or it may simply sound like another case of invasion.
Atlantic salmon are a key aquaculture species, especially off the coast of South America. Paradoxically, Atlantic salmon are endangered in the Atlantic Ocean, so farming them may be the only way to get them to your plate. However, these farms come at a cost to native organisms in the Pacific Ocean, including Pacific salmon.
Salmon farms are often densely populated, which may lead to increased diseases and pathogens that could spread to native salmon. Additionally, escaped Atlantic salmon may bully Pacific salmon out of their native spawning sites. Finally, although it appears Atlantic-Pacific salmon hybrids are difficult to produce, the fear of genetic interactions between salmon species still looms, especially among locally threatened and endangered Pacific salmon populations.
Why does an Atlantic salmon invasion matter? Pacific salmon play a key role in their native ecosystems. When juvenile salmon migrate to the ocean from the stream or lake where they were born, they are often no larger than your finger. Salmon feed and grow in the ocean for one to six years, depending on the species, putting on many pounds and growing to the length of your arm, but with much more mass. Pacific salmon only make one return migration to their home stream or lake, dying after spawning and protecting their nests for as long as they still have energy.
Salmon bring literally tons of nitrogen, phosphorus, and carbon with them, which fertilizes plants and animals in and around these freshwater ecosystems, from algae and fish to brown bears and trees (also recall that introduced salmon runs in the Great Lakes can also represent an influx of contaminants). In contrast to enriching freshwaters, salmon runs can also be a destructive force via upstream migration and digging of nests. Recent research has shown that stream structure is an important determinant of whether salmon have a net enrichment or disturbance effect on their natal surroundings. In contrast to native Pacific Salmon, Atlantic salmon will spawn in multiple years before dying, likely having a greater disturbance than enrichment effect since they take their nutrients back to the ocean with them after spawning. Therefore, if they invade and replace Pacific salmon, the natural ecological dyanmics will be severely disrupted.
With such important ecosystem impacts, it is worth giving some extra thought to sustainable consumption the next time you are planning a salmon meal, whether the Atlantic or Pacific variety.