One More Odd Thing I Just Learned About Fish: Rotting Salmon Impact Forest Ecology


When I’m not blogging for mental_floss, I can usually be found wearing bright orange rubber pants and gutting, cutting and selling fish at my local Whole Foods (and winning awards for it). Sometimes, my two worlds collide and I find some scientific research involving my ocean-dwelling friends that begs for a blog post. This is one of those times.

Poached with a little lemon and butter, grilled with a bourbon glaze, or left rotting on the ground for weeks—there’s no wrong way to serve salmon.

I don’t recommend that you try that last one, but for Canada’s temperate rainforests, it’s the best recipe there is. Biologist John Reynolds from Simon Fraser University just published the results of a study suggesting that salmon carcasses provide an important “nutrient subsidy” that influences plant growth and diversity in forests.

In the Great Bear Rainforest on British Columbia's central coast, thousands of salmon migrate up different streams and rivers to spawn each year. Bears, wolves, and other predators can sometimes move more than 50 percent of those fish from water to land when they catch dinner, eat what they want, and leave the rest where it falls. The carcasses then rot, passing their nutrients into the ground.

Reynolds and post-doctoral student Morgan Hocking spent four years trudging through old-growth forests looking for dead fish. Whenever they found a carcass, they analyzed any water and cataloged any plants that were nearby. They found that nitrogen released by the fish carcasses favors some plants, like the wonderfully named salmonberry and stink currant, but pushes out others that prefer nutrient-poor soil, like blueberries and false azaleas.

The change in plant density and diversity in the plant community, in turn, affects the animals and insects that use plants for food and shelter. This is, first and foremost, important information for conservationists to have. It’s also a humbling reminder that a sea change can start with something that might seem insignificant. It all starts with a dead fish.

Reference: Hocking, M. and Reynolds, D. (2011). "Impacts of Salmon on Riparian Plant Diversity." Science Vol. 331 no. 6024 pp. 1609-1612. DOI: 10.1126/science.1201079

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