A new paper in PLoS Biology by Levi and colleagues (here) describes a new approach for assessing trade-offs between economic and ecological goals in “Ecosystem Based Management” (EBM). The paper concludes:
“Commercial fisheries that harvest salmon for human consumption can end up diverting nutrients that would normally be directed to terrestrial and aquatic ecosystems. We examined this problem for Pacific salmon fisheries by using grizzly bears as indicators of salmon ecosystem function. Bear densities vary enormously depending on salmon availability, and by leaving uneaten salmon carcass remains beside spawning streams, bears play an important role in dispersing marine nutrients to plants, invertebrates, and other wildlife. By relating the number of spawning fish to bear diet and density, we developed a model to quantify ‘‘ecosystem-harvest’’ tradeoffs; i.e., how bear density changes with the amount of fish harvested (fishery yields). We estimated this tradeoff between yields and bear density for six sockeye salmon stocks in Alaska and British Columbia (BC) across a range of management options that varied the number of salmon allowed to escape from the fishery. Our model shows that bear densities will increase substantially with more spawning fish at all sites. Notably, in most study systems, fishery yields are also expected to increase as the number of spawning fish increases. There is one exception, however, in the Fraser River (BC), where bears are threatened and sockeye salmon are nearly the only species of salmon available. Here, releasing more salmon to spawn would result in lower fishery yields. To resolve such conflicts in this and other systems, we propose a generalizable ecosystem-based fisheries management framework, which allows decision-makers (such as fisheries managers and conservation scientists) to evaluate different allocation options between fisheries and other ecosystem recipients.”
In a news story from California (here), the study’s authors suggest that their conclusions are also relevant to areas where grizzly bears are extinct: “Levi argues that having more salmon in streams would also have economic benefits from better wildlife viewing opportunities. Increased salmon abundance would surely help California’s bald eagles. More salmon would be a boon to the state’s recovering eagle population. More salmon would also increase black bear populations, he says, which is good for both hunters and wildlife observers.”