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Fisheries management decisions are guided by the outcomes from stock assessment models, which typically assume that fish stocks represent single homogenous populations. However, species normally exhibit complex spatial structure. Using outputs from spatially aggregated stock assessment models to inform harvest strategies in spatially structured fisheries could lead to management failure and erosion of biocomplexity. This paper summarizes how spatial population structure has been addressed in the fisheries literature and explores options for developing harvest strategies that address fish population spatial structure. I also highlight common pitfalls and data needs associated with spatial modeling and harvest strategies. Continued investment in spatial and finer-scale data collection and associated spatial analysis are necessary to develop effective spatial harvest strategies. I conclude that developing spatial modelling and harvest strategies for fishery species is an important step to address the complex nature of marine population structure.
Ocean harvests have plateaued worldwide and many important commercial stocks have been depleted. This has caused great concern among scientists, fishery managers, the fishing community, and the public. This book evaluates the major models used for estimating the size and structure of marine fish populations (stock assessments) and changes in populations over time. It demonstrates how problems that may occur in fisheries dataâ€"for example underreporting or changes in the likelihood that fish can be caught with a given type of gearâ€"can seriously degrade the quality of stock assessments. The volume makes recommendations for means to improve stock assessments and their use in fishery management.
Management strategies to prevent overfishing while achieving optimum yield vary according to the available data and life history of the fished stock. I evaluated two sets of management strategies for Pacific coast rockfish: strategies to set harvest limits for data-poor stocks, and strategies intended to protect the age structure of fished stocks. Setting Harvest Limits for Data-poor Stocks - The collapse of canary rockfish, Sebastes pinniger, in the northeast Pacific began more than two decades before the stock was officially declared overfished. The 2006 reauthorization of the Magnuson-Stevens Fishery Conservation and Management Act requires a scientifically-based harvest limit for all fished stocks, including those with data limited to catch. Two such "data-poor" methods are currently in use for the management of west coast stocks, depletion-corrected average catch (DCAC) and depletion-based stock reduction analysis (DB-SRA). To evaluate the performance of each method when challenged with catch and biological uncertainty, I retrospectively applied the methods to the catch and biological data available at the time of the first and second canary rockfish stock assessments in 1984 and 1990. In 1980 canary rockfish would be classified as "data-poor", and in 1990 as "data-rich". To evaluate the sensitivity of DCAC and DB-SRA to error in the catch data, harvest limits were estimated using both the historic catch data from each assessment, and the reconstructed catch data from the most recent stock assessment. In addition, harvest limits were estimated using simulated catch data sets for the years 1916 to 1983 with increasing variability around the true catch. DCAC and DB-SRA estimated harvest limits were significantly lower than the catch recommended in both the data-poor and data-rich stock assessments, but higher than the "true" overfishing limit. Use of current catch data improved the estimated harvest limit when the stock was data-poor, but not when the stock was data-rich. The simple methods responded to increasing error in the catch time series with decreasing mean estimates of the harvest limit, indicating that these methods are highly precautionary for this species, when the catch time series is the only source of error. Age Structure Management Strategies - In a variable oceanographic environment, a population with many reproductive age classes benefits not only from the increased fecundity of older fish; but also, in some species, an increase in larval fitness. Older females may also spawn at different times or over longer periods than younger females, increasing the probability of larvae encountering favorable environmental conditions. Despite the accumulating evidence for the importance of age structure to long-term population viability in harvested fish populations, long-lived west coast rockfish (Genus Sebastes) are managed with a biomass-based harvest control rule. I compared three strategies for age structure management, and evaluated the strategies relative to the status quo, biomass-based harvest control rules, across three rockfish life histories. I examined the tradeoff between yield and traditional management reference points, as well as performance measures that could serve as management reference points for age structure. Yield was reduced by strategies that maintain "old growth" age structure, but annual variation in the catch and the probability of becoming overfished were also reduced. The longest-lived rockfish benefited the most from strategies that maintained older fish in the population through dome-shaped selectivity. The shorter-lived rockfish benefited from adjustments in the catch limit based on the age composition of the catch one year previous. Achieving "pretty good yield" with management strategies that also decrease the potential for overexploitation is an important goal for stocks that are well-studied and those that are poorly understood; these investigations contribute to a growing literature on alternative approaches to sustainable fisheries management.
The actual Code of conduct is also available (1996) (ISBN 9251038341).
Quantitative modeling methods have become a central tool in the management of harvested fish populations. This book examines how these modeling methods work, why they sometimes fail, and how they might be improved by incorporating larger ecological interactions. Fisheries Ecology and Management provides a broad introduction to the concepts and quantitative models needed to successfully manage fisheries. Walters and Martell develop models that account for key ecological dynamics such as trophic interactions, food webs, multi-species dynamics, risk-avoidance behavior, habitat selection and density-dependence. They treat fisheries policy development as a two-stage process, first identifying strategies for varying harvest in relation to changes in abundance, then finding ways to implement such strategies in terms of monitoring and regulatory procedures. This book provides a general framework for developing assessment models in terms of state-observation dynamics hypotheses, and points out that most fisheries assessment failures have been due to inappropriate observation model hypotheses rather than faulty models for ecological dynamics. Intended as a text in upper division and graduate classes on fisheries assessment and management, this useful guide will also be widely read by ecologists and fisheries scientists.
Papers presented: 1) Reference points for fisheries management: the western Canadian experience; 2) Reference points for fisheries management: the eastern Canadian experience; 3) Reference points for fisheries management: the ICES experience; 4) Spawning stock biomass per recruit in fisheries management: foundation and current use; 5) The development of a management procedure for the South African anchovy resource; 6) How much spawning per recruit is enough?; 7) The behaviour of Flow, Fmed and Fhigh in response to variation in parameters used for their estimation; 8) The Barents Sea capelin stock collapse: a lesson to learn; 9) Variance estimates for fisheries assessment: their importance and how best to evaluate them; 10) Evaluating the accuracy of projected catch estimates from sequential population analysis and trawl survey abundance estimates; 11) Bootstrap estimates of ADAPT parameters, their projection in risk analysis and their retrospective patterns; 12) Analytical estimates of reliability for the projected yield from commercial fisheries; 13) Risk evaluation of the 10% harvest rate procedure for capelin in NAFO Division 3L; 14) Using jackknife and Monte Carlo simulation techniques to evaluate forecast models for Atlantic salmon; 15) Monte Carlo evaluation of risks for biological reference points used in New Zealand fishery assessments; 16) A comparison of event free risk analysis to Ricker spawner-recruit simulation: an example with Atlantic menhaden; 17) Choosing a management strategy for stock rebuilding when control is uncertain; 18) Risks and uncertainties in the management of a single-cohort squid fishery: the Falkland Islands Illex fishery as an example; 19) Risks of over- and under-fishing new resources; 20) Estimation of density-dependent natural mortality in British Columbia herring stocks through SSPA and its impact on sustainable harvesting strategies; 21) The comparative performance of production-model and ad hoc tuned VPA based feedback-control management procedures for the stock of Cape hake off the west coast of Africa; 22) A proposal for a threshold stock size and maximum fishing mortality rate; 23) Biological reference points for Canadian Atlantic gadoid stocks; 24) Stochastic locally-optimal harvesting; 25) ITQ based fisheries management; 26) Bioeconomic methods for determining TACs; 27) Management strategies: fixed or variable catch quotas; 28) Bioeconomic impacts of TAC adjustment strategies: a model applied to northern cod; 29) Experimental management programs for two rockfish stocks off British Columbia; 30)A brief overview of the experimental approach to reducing uncertainty in fisheries management; 31) Fisheries management organizations: a study of uncertainty.
This book integrates the science of wildlife and fisheries. Updates include coverage of geographic information systems and biotelemetry; preferred structures for fish aging; information on diseases such as chronic wasting disease, avian flu, West Nile virus, viral haemorrhagic septicemia, and whirling disease.
A key goal of fisheries management is to regulate extractive pressure on a resource so as to ensure social, economic and ecological sustainability. This text provides an accessible entry point for students and professionals to management science as developed in fisheries, in order to facilitate uptake of the latest ideas and methods. Traditional management approaches have relied upon a stock assessment based on existing understanding of resource status and dynamics, and a prediction of the likely future response to a static management proposal. However all such predictions include an inherent degree of uncertainty, and the last few decades have seen the emergence of an adaptive approach that uses feedback control to account for unknown future behaviour. Feedback is achieved via a control rule, which defines a relationship between perceived status of the resource and a management action. Evaluations of such rules usually include computer simulation testing across a broad range of uncertainties, so that an appropriate and robust rule can be selected by stakeholders and managers. The book focuses on this approach, which is usually referred to as Management Strategy Evaluation. The book is enriched by case study examples from different parts of the world, as well as insights into the theory and practice from those actively involved in the science of fisheries management.
Thoroughly updated, with an inviting new design, the Second Edition offers the most current and accessible coverage of essential biological concepts and their applications, principles of resource management and conservation, and contemporary and public policy issues affecting today’s scientists and resources.