Assessment of Alternative Harvest Regulations for Sustaining Recreational Fisheries: Model Development and Application to Bull Trout

Abstract

Abstract.—Regulations designed to protect recreational fisheries from overexploitation can fail. Regulations such as size and bag limits restrict harvest by individual anglers but not angler effort and therefore not total harvest. Even when individual harvest limits are set to zero (i.e., catch and release), a combination of hooking mortality and noncompliance may lead to fishing mortality rates that are not sustainable if angling effort is sufficiently high. These assertions were tested and quantified by using simulation experiments on a size- and age-structured model developed for a fishery on an adfluvial bull trout population. The functions and rates describing the biology and fishery were derived from a variety of sources, including published and unpublished information on bull trout and, where such sources were unavailable, from other salmonid species. The model predicts that a 40-cm minimum size limit for harvest would maintain viable populations at an annual effort up to 4 angler-hours · ha1 · year1, a 65-cm minimum size limit up to 10 angler- hours · ha1 · year1, and a catch-and-release fishery up to 18 angler-hours · ha1 · year1. The quality of the fisheries that developed under these three alternative regulations varied substantially with the amount of angler effort imposed. Uncertainty in the minimum population size necessary to ensure sustainability, recruits per unit stock, catchability, hooking mortality rate, and noncompli- ance rate modifies quantitative predictions, but the qualitative patterns are general. If anglers respond dynamically to variation in the quality of fishing, then the ability of size limit regulations to sustain fisheries is further compromised. The combination of life history and fishery traits such as slow growth, late age at maturity, low fecundity, longevity, and high catchability render adfluvial bull trout particularly susceptible to overfishing, even within relatively narrow bounds of angler effort. A common management response to reduced