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Angler effort is an important factor affecting recreational fisheries. However, angler responses are rarely incorporated into recreational fisheries regulations or predictions. Few have attempted to examine how daily bag limit regulations affect total angling pressure and subsequent stock densities. Our paper develops a theoretical basis for predicting angler effort and harvest rate based on stock densities and bag limit regulations. We examined data from a management system that controls the total exploitation of walleyes Sander vitreus (formerly Stizostedion vitreum) in northern Wisconsin lakes and compared these empirical results with the predictions from a theoretical effort and harvest rate response model. The data indicated that higher general angler effort occurs on lakes regulated with a 5‐walleye daily limit than on lakes regulated with either a 2‐ or 3‐walleye daily limit. General walleye catch rates were lower on lakes with a 5‐walleye limit than on lakes with either a 2‐ or 3‐walleye daily limit. An effort response model predicted a logarithmic relationship between angler effort and adult walleye density and that an index of attractiveness would be greater on lakes with high bag limits. Predictions from the harvest rate model with constant walleye catchability indicated that harvest rates increased nonlinearly with increasing density. When the effort model was fitted to data from northern Wisconsin, we found higher lake attractiveness at 5‐walleye‐limit lakes. We conclude that different groups of anglers respond differently to bag limit changes and that reliance on daily bag limits may not be sufficient to maintain high walleye densities in some lakes in this region.

A freshwater sport fishery that targets hundreds of geographically isolated stocks is simulated by combining a model of angler behavior with a model of rainbow trout (Oncorhynchus mykiss) population dynamics. Ideal free distribution (IFD) theory, which suggests that angling quality will be similar on all lakes, is used to drive angler effort distribution. Model parameters are based on creel survey data from 53 lakes and empirical relationships between growth, survival, and density derived from whole-lake density manipulations on nine lakes over a period of 10 years. We compared angling quality, population density, fish size, and yield under unfished conditions, harvest rates that maximize sustained yields (MSY), and an IFD equilibrium driven by angler behavior. The IFD equilibrium rarely maximized yields. Stocks with high MSY angling quality are overexploited at the IFD equilibrium because anglers move to take advantage of exceptional angling opportunities. These stocks would often be viewed as more resistant to harvest pressure because they have higher stock productivities and habitat capacities. However, in our model, they are systematically overharvested because their high fish density attracts excessive angling pressure. Conversely, stocks with low MSY angling quality are underexploited because anglers move to take advantage of better angling quality on other lakes.

Because fisheries operate within a complex array of species interactions, scientists increasingly recommend multispecies approaches to fisheries management. We created a food web model for the Baltic Sea proper, using the Ecopath with Ecosim software, to evaluate interactions between fisheries and the food web from 1974 to 2000. The model was based largely on values generated by multispecies virtual population analysis (MSVPA). Ecosim outputs closely reproduced MSVPA biomass estimates and catch data for sprat (Sprattus sprattus), herring (Clupea harengus), and cod (Gadus morhua), but only after making adjustments to cod recruitment, to vulnerability to predation of specific species, and to foraging times. Among the necessary adjustments were divergent trophic relationships between cod and clupeids: cod exhibited top-down control on sprat biomass, but had little influence on herring. Fishing, the chief source of mortality for cod and herring, and cod reproduction, as driven by oceanographic conditions as well as unexplained variability, were also key structuring forces. The model generated many hypotheses about relationships between key biota in the Baltic Sea food web and may ultimately provide a basis for estimating community responses to management actions.

Pelagic fisheries in the Pacific Ocean target both large (Thunnus spp.) and small tunas (juveniles of Thunnus spp; Katsuwonus pelamis) but also take billfishes (Xiphias gladius, Makaira spp., Tetrapturus spp., Istiophorus platypterus) and sharks (Prionace glauca, Alopias superciliosus, Isurus oxyrinchus, Carcharhinus longimanus, Galeocerdo cuvieri) as bycatch. We developed a multispecies model using the Ecopath with Ecosim software that incorporated time-series estimates of biomass, fishing mortality, and bycatch rates to evaluate the relative contributions of fishing and trophic impacts on tuna dynamics in the central Pacific (0°N to 40°N and 130°E to 150°W). The Ecosim model reproduced the observed trends in abundance indices and biomass estimates for most large tunas and billfishes. A decline in predation mortality owing to depletion of large predators was greatest for small yellowfin tuna and could possibly account for apparent increases in biomass. For other tunas, however, predicted changes in predation mortality rates were small (small bigeye) or were overwhelmed by much larger increases in fishing mortality (skipjack and small albacore). Limited evidence of trophic impacts associated with declining apex predator abundance likely results from the difficulties of applying detailed trophic models to open ocean systems in which ecological and fishery data uncertainties are large.Résumé : Les pêches commerciales dans le Pacifique ciblent les thons, tant de grande (Thunnus spp.) que de petite taille (jeunes Thunnus spp.; Katsuwonus pelamis), mais elles récoltent aussi les espadons et les voiliers (Xiphias gladius, Makaira spp., Tetrapturus spp., Istiophorus platypterus), ainsi que les requins (Prionace glauca, Alopias superciliosus, Isurus oxyrinchus, Carcharhinus longimanus, Galeocerdo cuvieri) comme prises accessoires. Nous avons mis au point un modèle multispécifique basé sur le logiciel Ecopath additionné de Ecosim qui incorpore les séries temporelles d'estimations de la biomasse, de la mortalité due à la pêche et des taux de prises accessoires (1952-1998) pour évaluer les contributions relatives de la pêche et des impacts trophiques à la dynamique des populations de thons du centre du Pacifique (0°N à 40°N et 130°E à 150°O). Le modèle Ecosim reproduit les tendances observées des indices d'abondance et des estimations de biomasse chez les grands thons, ainsi que chez les espadons et les voiliers. Le déclin de la mortalité due à la prédation causée par l'épuisement des populations de grands prédateurs est maximal chez les petits albacores à nageoires jaunes et peut sans doute expliquer les augmentations apparentes de la biomasse. Chez les autres thons, cependant, les changements prédits de la mortalité due à la prédation sont ou bien faibles (petits thons ventrus), ou alors masqués par des augmentations beaucoup plus importantes de la mortalité due à la pêche (thonines à ventre rayé et petits germons). Les indications partielles qui laissent croire à l'existence d'impacts trophiques associés au déclin des...

We developed and evaluated a new model for predicting exploitation from recreational fishing effort. The model assumes that fish exchange between available and unavailable states and that fishery catches are taken only from the available pool. This limited vulnerability model exhibits a nonlinear, negative relationship between fishing effort and catch rate that manifests itself in the effort−exploitation relationship as an apparent decline in catchability with increasing effort. Decreasing catchability leads to an exploitation rate asymptote that may be less than unity as well as to a wide range of fishing effort over which exploitation is insensitive to changes in effort. Model predictions were consistent with the observed relationship between fishing effort and exploitation obtained from creel surveys and mark–recapture studies on rainbow trout Oncorhynchus mykiss lakes in British Columbia. We combined the exploitation modeling approach with an age‐structured model for a naturally reproducing rainbow trout population to evaluate both optimum fishing effort policies and critical fishing effort levels that lead to population collapse. Optimum fishing effort (±SD) was 18.8 ± 3.7 angler‐days/ha (AD/ha) for a stock that exhibits high recruitment compensation and 9.4 ± 2.4 AD/ha for a stock with low recruitment compensation. Critical effort did not exist for the high‐compensation scenario; the estimate of critical effort for the low‐compensation scenario was 23.2 ± 5.1 AD/ha. The estimator traditionally used to predict exploitation gave a poor fit to observed data, and resulting effort levels were twice those obtained from the limited vulnerability model.

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Recreational fisheries are increasingly faced with the dilemma of “too many people chasing too few fish.” Active management of angler effort promises relief from the pressures of overcrowding and declines in angling quality. In this paper, we develop a regional‐scale model of recreational fishery dynamics to evaluate how active effort management policies might affect the cumulative value taken over many fisheries. The model incorporates linear increases in satisfaction per angler‐day with increases in catch rate to represent demand, declines in catch rate with increasing effort to represent supply limitations, and angler movement among open‐access fisheries to represent the presence of uncontrolled, open‐access alternatives to effort‐managed fisheries. The management control variables were the proportion of fisheries managed under effort control (Pm) and the proportion of open‐access effort allowed on managed lakes (Pe). Unmanaged lakes remained open access. Policies that maximized total regional value favored effort management for all combinations of Pm and Pe. The total increases in value over open‐access conditions were greatest under conditions of high demand and low effort movement. When effort movement and demand for improved quality were both high, a large proportion (>50%) of fisheries needed to be included under effort control to offset the value losses on open‐access fisheries. Because effort management offers promise for creating above‐average fishing opportunities, managers should carefully consider regional‐scale impacts and the potential demand for high‐quality, low‐effort angling opportunities.