Research out of SFU indicates that the coho salmon population may benefit from nutrients scavenged from the decaying bodies of their distant pink and chum cousins. 

Michelle Nelson, lead author of a recent report on the subject, explained, “This is the first study to look at the effects of spawning salmon on the population of another species of salmon.” She conducted the study for her PhD project along with her advisor, SFU professor of aquatic ecology and conservation, John Reynolds.

Nelson found a strong correlation between an abundance of baby coho salmon and high numbers of pink and chum salmon. In fact, “there were three times more baby coho salmon in streams with high numbers of pink and chum spawning salmon compared to those with none,” she said.

Nelson surveyed the coho salmon populations in over 20 streams in the Great Bear Rainforest. With the help of the Heiltsuk First Nations, Raincoast Conservation Society, and several members of the Reynolds research group, she did so by collecting data on the habitat characteristics of the streams and by counting the pink and chum salmon during spawning. 

With the data she collected, Nelson was able to create and test candidate models to determine the importance of pink and chum salmon in predicting juvenile coho salmon abundance.

These findings could indicate that juvenile coho are thriving by consuming eggs and tissues of the decaying adult pink and chum salmon. However, it was observed that there were similar benefits in populations of juvenile coho that were too young to have had contact with the other spawning species. 

The latter sort of benefit is considered to be indirect, and there are several different pathways by which nutrients travel that could explain the results. 

For example, the decaying bodies of the spawning salmon could provide the dissolved nutrients needed for the stream biofilm — the slimy algae found on solid underwater surfaces. The biofilm acts as a primary producer and is fed upon by aquatic invertebrates, who are subsequently fed upon by the juvenile coho.

Terrestrial invertebrates, such as flies, may also feed upon the carcasses of the pink and chum that decompose on the shore after being fed upon by wolves or bears. The larvae and/or adults could then provide a food source for the juvenile coho.

With further research, Nelson hopes to better understand these pathways and important “salmon-to-salmon interactions.” 

For researchers, this study reinforces the fact that diversity is key to maintaining healthy ecosystems. Nelson explained that the “circle of salmon” is just a small part of our delicate aquatic ecosystems, the complexity of which we are only beginning to understand.