Assessing the effects of catch and release regulations on a quality adfluvial brook trout population using a computer based age-structure model

As populations of wild brook trout Salvelinus fontinalis decline across the species' native range in North America, angling regulations such as fly-fishing only and catch and release are being used by management agencies to conserve fish while maintaining angling opportunities. Postrelease (hooking) mortality may significantly shift the age structure and size structure of populations. To assess the possible influence of catch-and-release fishing on brook trout population structure, we applied data from several sources to build a deterministic population model that included age-classes up to age 5. To assess the potential effect of fishing, we examined the changes in population density and age structure at varying levels of angler effort (0–400 angler-hours·ha⁻¹·year⁻¹) and hooking mortality rates (0–14%). Assuming a low (5%) hooking mortality rate, trophy brook trout density (ages 4 and 5) decreased by 50% at an angling intensity of 160 angler-hours·ha⁻¹·year⁻¹. As angling effort increased, the proportion of older fish (ages 3–5) declined further. At very high levels of angling effort (>300 angler-hours·ha⁻¹·year⁻¹), age-4 and age-5 fish were eliminated from the population. Increases in postrelease mortality rates resulted in similar declines for older age-classes. The results of this simulation indicate that hooking mortality rates as might be common in catch-and-release fisheries may significantly shift the age structure of a population, thus reducing trophy angling potential.