Figure 5. Using bears for ecosystem-based management in Chilko and Quesnel.

(A) The relative bear density (solid) and relative fisheries yield (hatched) across a range of sockeye salmon escapements in Chilko and Quesnel (Fraser River) systems from British Columbia (BC), Canada. Ecosystem-based escapement goals, E_EBM, occur where the curves meet, indicating that bears and fishery yields are equally reduced from their maxima (double-sided arrows). Increases in escapement from E_MSY (maximum sustainable yield escapements; dashed arrows) to E_EBM (dotted arrows) reduce harvests to some fraction of MSY. (B) Tradeoffs between loss in fisheries yield and increase in grizzly bear densities for escapements greater than those corresponding to MSY. Green dots indicate proposed ecosystem-based management escapements (E_EBM) for each system. Reduction in fishery yields can result in substantial increases in bear density. (C) However, increased salmon allocations to bears (gray) under E_EBM provide much higher nutrient subsidies to terrestrial and aquatic systems than either the percent increase in bear densities (red) or decrease in fishery yields (yellow), which we suggest is due to the shape of the stock-recruitment relationships.