Merging Angler and Fish Behaviour into Fisheries Models

Recreational fisheries management attempts to balance conflicting objectives related to fishing opportunities, fishing quality, and conservation of fish stocks.  However, the highly dynamic behavioural responses of fish populations and anglers are rarely considered when developing management strategies and tactics.  Instead, managers often assume that supply-side (e.g., stocking, enhancement) and demand-side (e.g., regulations) tactics work independently.  Ignoring the system structure of recreational fisheries leaves management vulnerable to surprises and failure to meet objectives.  In this paper, we develop a new system dynamics approach for modeling recreational fisheries that integrates three main components: (i) an angler numerical response model to fish population dynamics and harvest regulations; (ii) a fish availability model involving three behavioural states (invulnerable, vulnerable, and recovering from catch-and-release); and (iii) a population dynamics model for fish that accounts for natural mortality, harvest mortality, and catch-and-release mortality.  The model is used to make forecasts for effort levels, average angler catch rates, and fish population sizes for inputs including stocking rates (or stock-recruitment relationships), size-at-stocking, and bag- and size-limit regulations.  Extending the model to naturally reproducing stocks is straightforward.  We review a series of case examples that qualitatively agree with model predictions about exploitation rates as well as impacts of regulations such as fishery openings, bag limits, and catch-and-release restrictions.  We then show quantitative model fits to daily catch and effort for rainbow trout (Oncorhynchus mykiss) fisheries on 6 urban experimental lakes around Vancouver, British Columbia and annual (1986-2009) catch-effort data for 36 put-grow-and-take fisheries in British Columbia's southern interior.