Management Objectives Drive Optimal Stocking Strategies – a Modelling Approach

Stocking fish into wild populations, to maintain or enhance fish stocks and angler satisfaction, is common in recreational fisheries. Development of sustainable stocking strategies, however, is challenging. Natural variation in fish abundance and interactions between wild and stocked fish can have unexpected consequences for stocking outcomes, as do uncertain responses of anglers to stocking measures or harvest limits. Particularly the latter is often ignored in stocking decisions and models. We developed a bio-economic model of a stock-enhanced recreational fishery of northern pike (Esox Lucius). It incorporates dynamic angler behaviour that was informed by empirical surveys. We defined management objectives ranging from “angler-pleasing” to “conservation-oriented” and investigated stocking of different sized fish. We found that in high quality habitats which support naturally reproducing pike stocks, the objectives of both angler-pleasing and conservation-oriented strategies can best be achieved at intermediate minimum-size limits without stocking. By contrast, in low quality habitats with limited natural recruitment, stocking and minimum-size limit adjustments are needed to maximize angler-oriented management objectives. Here benefits increase with increasing size-at-release. This contradicts the common perception that stocking small fish is superior to larger fish. The results show that optimal stocking policies can vary considerably depending on the management objective and the natural productivity of the fishery.