© 2015 by Salmon Watersheds Lab

Dendritic biodiversity and stability of First Nations fisheries throughout the Fraser River watershed

 

Holly studied the effect of population diversity on the catch stability of First Nations salmon fisheries throughout the Fraser River watershed. The result of increased diversity on ecological stability has been termed the ‘portfolio effect’ and is analogous to financial theory, whereby asset diversification stabilizes the total value of a portfolio. Borrowing from financial portfolio theory then, populations are analogous to assets, where asynchronous population dynamics improve the stability of the fishery, i.e. the portfolio. Watersheds provide an ideal system for examining the effect of diversity on ecosystem stability due to their dendritic structures, where smaller tributaries flow into larger stream segments, similar to the branching of a tree. As salmon migrate upstream from the ocean to their spawning habitats, populations diverge from the main channel, reducing the amount of diversity in the river at every branching point. For her Master’s thesis, she examined the effect of salmon population diversity on the stability of catch over time within the Fraser River, a large watershed (220,000 km2) in BC. She compiled yearly catch data (1951-2012) of Chinook, chum, coho, pink, and sockeye salmon from Fisheries and Oceans Canada (DFO) on 16 First Nations fisheries located throughout the watershed.

 

Her findings suggest that population-level biodiversity can increase fishery stability across years. This study highlights the importance of biodiversity for holistic fisheries management. As DFO moves towards ecosystem-based management approaches, new methods for reducing by-catch (fish that are not targeted) of protected or declining populations are being considered. In the Skeena River (BC), there is ongoing dialogue to move fisheries farther upstream to better target specific populations and reduce by-catch. Results from this study could be used to inform fishery placement through analysis of trade-offs between a fishery’s stability and its by-catch. Relevant to management, her work provides a striking example of diversity driving portfolio effects at large spatial scales.

Holly's thesis project combined fisheries science and management and provided novel insights in ecological theory with broader applications in fisheries management.

Current Position: Associate, Compass Resource Management Ltd., Vancouver,

 

Holly Nesbitt