Declining salmon runs on the west coast of North America have triggered a cascade of fishery closures over the last few decades. Now, biologists are interested in seeing how the loss of salmon is affecting one of their top predators; grizzly bears.
Grizzlies in British Columbia, Canada rely on the migration of millions of adult salmon from the ocean into streams throughout the spring and summer. As salmon swim upriver in search of habitat to lay their eggs, bears snag these fatty, nutritious fish. This diet allows bears to bulk up and store the fat needed to get them through winter hibernation.
However, fewer salmon may mean many bears, including cubs, won’t survive the harsh Canadian winters.
Researchers from the Canadian government and universities are teaming up to study the health of the grizzly populations that depend on salmon. Carrying out helicopter surveys and using genetic analysis on grizzly hair samples, they are able to see how grizzly numbers fluctuate between years with healthy and poor salmon runs.
Bears play an important role in fertilizing the floors of the forest they live in. Bear droppings are rich in nutrients like nitrogen and phosphorus because of their diet. Often, these nutrients are in scarce quantities on forest floors. Therefore, the bears act as a “conveyor belt”, moving nutrients into the forest. “As we lose bears or salmon or both…” says retired wildlife biologist Barry Gilbert, “…then we’re also affecting the health of the forests”.
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- Tara Duffy, Stony Brook University