Study: Allowing More Salmon to Spawn Creates a Win-Win for Humans and Ecosystems
Salmon spend most of their lives in the ocean, but return to their birthplaces in freshwater streams to spawn the next generation. These annual migrations up and down the inland rivers are well known and play a significant role in the ecosystem, particularly in the Pacific Northwest. However, there is a concern that humans are harvesting too many salmon, not allowing enough to return upstream to reproduce. This leaves little for the species which depend on the salmon runs such as grizzly bears. A new research study suggests that more Pacific salmon should be allowed to spawn in coastal streams, which would create a win-win for humans and the natural environment.
The study was conducted by researchers from University of California (UC) Santa Cruz and Canada. Lead author, Taal Levi, notes that salmon fisheries are generally well managed. Those in charge determine how many salmon to allocate to spawning and how many to harvest. The concern is that the proportion of spawning to harvest is skewed and needs to be rebalanced for sustainability.
To assess their theory, the researchers examined the relationship between salmon and 18 grizzly bear populations in British Columbia, and what percentage of the bears' diet was made up of salmon.
"We asked, is it enough for the ecosystem? What would happen if you increase escapement—the number of fish being released? We found that in most cases, bears, fishers, and ecosystems would mutually benefit," Levi said.
An increase in spawning salmon will allow more food for the bears. Plus, more uneaten fish remains will be left behind by the bears if the streams are more packed with salmon. The bears would choose to eat only the most nutrient-rich parts such as the brain and eggs. The leftover fish carcasses could then feed a variety of other scavenging animals. This would create richer biodiversity and a healthier ecosystem.
In most instances, more salmon allowed to spawn will also allow more young salmon reach the ocean, translating into larger harvests for fishermen. The initial cut in the amount of fish harvested would be hard at first, but could eventually lead to overall greater numbers.
However, in two of the systems studied in the Fraser River, B.C., helping the ecosystem with more spawning salmon would hurt the fisheries. The predicted economic cost would be $500,000-700,000 per year.
The study has been published in the journal, PLoS Biology.
For more information on sustainable seafood, check out the Marine Stewardship Council.
Grizzly Bear and Salmon image via Shutterstock