Fishery managers already let a certain number of salmon slip away so those fish can spawn. But it’s not clear which “escapement” level is best for the fisheries and the ecosystem. Grizzly bears eat salmon and often leave the remains of their meals by streams, providing nutrients for plants and animals. And the number of spawning fish also affects fishery yields down the line.
Researchers tackled the problem by modelling the effects of different escapement levels for four coastal sockeye salmon stocks and two inland stocks in Alaska and British Columbia, Canada. In the coastal systems, leaving more salmon to spawn would increase bear density by 8 to 44 percent. Fishery yields would jump as well — “an apparent win-win situation,” the authors write.
The situation wasn’t as rosy for the two inland stocks in Fraser River, Canada, where few salmon species besides sockeye exist. Bears would benefit from more sockeye salmon escaping, but fishery yields would drop.
Nevertheless, the team suggests that the research offers a way to balance ecosystem and fishery trade-offs. While a system that values ecosystems and fisheries equally “might not be socio-politically possible,” the researchers write, the model “allows estimation of costs and benefits associated with adjustments to escapement in either direction.” — Roberta Kwok | 10 April 2012
Source: Levi, Taal et al. 2012. Using grizzly bears to assess harvest-ecosystem tradeoffs in salmon fisheries. PLoS Biology doi: 10.1371/journal.pbio.1001303.
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