Sean P. Cox

Canada's Recreational Fisheries: The Invisible Collapse?

Abstract Fishing for recreation is a popular activity in many parts of the world and this activity has led to the development of a sector of substantial social and economic value worldwide. The maintenance of this sector depends on the ability of aquatic ecosystems to provide fishery harvest. We are currently witnessing the collapse of many commercial marine fisheries due to over-exploitation. Recreational fisheries are typically viewed as different from commercial fisheries in that they are self-sustaining and not controlled by the social and economic forces of the open market that have driven many commercial fisheries to collapse. Here we reject the view that recreational and commercial fisheries are inherently different and demonstrate several mechanisms that can lead to the collapse of recreational fisheries. Data from four high profile Canadian recreational fisheries show dramatic declines over the last several decades yet these declines have gone largely unnoticed by fishery scientists, managers, an...

An ecosystem model of food web and fisheries interactions in the Baltic Sea

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.

Modeling Exploitation in Recreational Fisheries and Implications for Effort Management on British Columbia Rainbow Trout Lakes

Abstract 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 r...

Impacts of Daily Bag Limit Reductions on Angler Effort in Wisconsin Walleye Lakes

Abstract 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 ...

A Model-Based Evaluation of Active Management of Recreational Fishing Effort

Abstract 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 (P m) and the proportion of open-access effort allowed on managed lakes (P e). Unmanaged lakes remained open access. Policies that maximized total region...

Managing Baltic Sea Fisheries under Contrasting Production and Predation Regimes: Ecosystem Model Analyses

Abstract Based on an earlier published ecosystem model, we have explored possible effects of different management scenarios for the Baltic Sea. The scenarios include an oligotrophication of the system, a drastic increase in the number of seals, and changes in the fishery management. From these simulations we conclude that fisheries, seals, and eutrophication all have strong and interacting impacts on the ecosystem. These interactions call for integrated management. The modeling highlights the potential for conflicts among management mandates such as flourishing fisheries, rebuilt seal populations, and substantially reduced eutrophication. The results also suggest that fisheries management reference points have to be adjusted in response to changes in the presence of natural predators or ecosystem productivity.

Evaluation of a Management System for a Mixed Walleye Spearing and Angling Fishery in Northern Wisconsin

Abstract In response to Chippewa tribal harvest declarations, the state of Wisconsin lowers daily angling bag limits for walleye Stizostedion vitreum in an attempt to avoid a maximum adult walleye exploitation of 35% on more than 1 in 40 occasions. We asked whether uncertainty in estimates of total allowable catch (TAC) and the sliding bag limit system used to manage anglers allowed the state to meet the overharvest risk level. During 1990–1998, 20–25 lakes were randomly sampled each year to estimate adult walleye stock and walleye harvest by angling and spearing. Adult walleye exploitation was calculated as the sum of angling and spearing exploitation rates. Adult walleye exploitation rates averaged 11.83% and did not vary significantly among years during 1990–1998. Angling exploitation averaged 8.38%, and spearing exploitation averaged 3.45%. Out of 210 lakes sampled during 1990–1998, only 4 (1.9%) had total exploitation rates that exceeded 35%. Since the exploitation rates were measured with error, we ...

Circle Hooks for Pacific Longliners: Not a Panacea for Marlin and Shark Bycatch, but Part of the Solution

Abstract Blue marlin Makaira nigricans, striped marlin Tetrapturus audax, and pelagic sharks (e.g., blue shark Prionace glauca) are commonly caught as bycatch by longline fisheries in the central North Pacific Ocean. Recently, concern has increased about depletion of these species. Modifications in longline gear may offer one solution. Here, we test the use of circle hooks, rather than the conventional tuna-style hooks, on longlines using an ecosystem model of the central North Pacific Ocean. The simulations considered span a range of reasonable circle hook catchability and survival rates for released fish. The results suggest that if circle hooks have higher catchability than the currently used tuna-style hooks, switching to circle hooks depletes marlin biomass by 25–40% and shark biomass by 15–35% over 30 years. However, these depletions do not occur if circle hook catchability is equal to or lower than that of tuna-style hooks. When the effects of catch-and-release requirements for marlins and sharks w...

The roles of biological reference points and operational control points in management procedures for the sablefish ( Anoplopoma fimbria ) fishery in British Columbia, Canada

Biological reference points (BRPs) in fisheries policy are typically sensitive to stock assessment model assumptions, thus increasing uncertainty in harvest decision-making and potentially blocking adoption of precautionary harvest policies. A collaborative management strategy evaluation approach and closed-loop simulation modelling was used to evaluate expected fishery economic and conservation performance of the sablefish ( Anoplopoma fimbria ) fishery in British Columbia (Canada), in the presence of uncertainty about BRPs. Comparison of models derived using two precautionary harvest control rules, which each complied with biological conservation objectives and short-term economic objectives given by industry, suggested that both rules were likely to avert biomass decline below limit BRPs, even when stock biomass and production were persistently overestimated by stock assessment models. The slightly less conservative, industry-preferred harvest control rule also avoided short-term economic losses of c. CAN

In-Season Forecasting of Coho Salmon Marine Survival via Coded Wire Tag Recoveries

2.7–10 million annually, or 10–50% of current landed value. Distinguishing between the role of BRPs in setting fishery conservation objectives and operational control points that define harvest control rules improved the flexibility of the sablefish management system, and has led to adoption of precautionary management procedures.