Kenneth M. Leber

Responsible Approach to Marine Stock Enhancement: An Update

Marine stock enhancement is a set of management approaches involving the release of cultured organisms to enhance or restore fisheries. Such practices, including sea ranching, stock enhancement, and restocking, are widespread, of variable success, and often controversial. A set of principles aimed at promoting responsible development of restocking, stock enhancement, and sea ranching has been proposed by Blankenship and Leber [American Fisheries Society Symposia 15: 167–175 (1995)], and has gained widespread acceptance as the ‘Responsible Approach’. Fisheries science and management, in general, and many aspects of fisheries enhancement have developed rapidly since the responsible approach was first formulated. Here we provide an update to the Responsible Approach in light of these developments. The updated approach emphasizes the need for taking a broad and integrated view of the role of enhancements within fisheries management systems; using a stakeholder participatory and scientifically informed, accountable planning process; and assessing the potential contribution of enhancement and alternative or additional measures to fisheries management goals early on in the development or reform process. Progress in fisheries assessment methods applicable to enhancements and in fisheries governance provides the means for practical implementation of the updated approach.

A New Era for Restocking, Stock Enhancement and Sea Ranching of Coastal Fisheries Resources

The growing number of countries investigating the potential for releasing cultured juveniles to augment coastal fisheries resulted in the First International Symposium on Stock Enhancement and Sea Ranching (ISSESR) in Norway in 1997. The 1st and 2nd ISSESR, in Japan in 2002, were instrumental in developing methods for mass production of environmentally fit juveniles and for releasing them in responsible ways. The 3rd ISSESR, held in the U.S.A. in 2006 (www.SeaRanching.org), ushered the discipline into a new era. The major advances included: (1) definitions of the various objectives for releasing cultured juveniles (restocking, stock enhancement, and sea ranching); (2) a framework for integrating releases within their fisheries management context, including tools for quantitative assessment; (3) a systematic, transparent, and stakeholder-participatory planning process to determine whether releases have a cost-effective role to play in managing a fishery; (4) a comprehensive case study (blue crabs in Chesapeake Bay) describing the multi-disciplinary approach needed to evaluate the potential benefits of releases; and (5) a suite of other lessons to guide stakeholders in evaluating the potential for and implementation of releases. The papers in this Special Issue of Reviews in Fisheries Science elaborate how restocking, stock enhancement and sea ranching programs can create synergies between aquaculture and some coastal fisheries to help meet the future demand for seafood and aid in restoring depleted stocks.

An Evaluation of Coded Wire and Elastomer Tag Performance in Juvenile Common Snook under Field and Laboratory Conditions

Abstract From 1997 to 2002, retention of coded wire tags (CWTs) and visible implant elastomer (VIE) tags was evaluated in a series of stock enhancement studies with common snook Centropomus undecimalis (60–230 mm fork length (FL)). These experiments were conducted in both field and laboratory settings in Sarasota, Florida. Retention rates of CWTs were stable after 30 d and remained greater than 97% even 1 year after tagging. Retention of VIE tags was compared among different body implant locations, implant techniques, and fish sizes. Body location had the strongest influence on VIE retention, and tags implanted in the fins (anal and caudal) had significantly higher retention rates (mean ± SE = 76 ± 9%) than those implanted in the head (adipose eyelid, jaw, and preorbital nose tissue; 5.6 ± 1.8%, P = 0.038) 1 year after tagging. After 1 year, however, most VIE tags—regardless of body location—were nearly indistinguishable or lost. Fish implanted with two VIE marks had consistently higher mean tag retention...

Marine Stock Enhancement in Florida: A Multi-Disciplinary, Stakeholder-Supported, Accountability-Based Approach

Saltwater fishery management in Florida, USA, is mandated to include user-supported hatchery-based stock enhancement. Scientists at the Florida Fish and Wildlife Conservation Commission and Mote Marine Laboratory have taken a multi-disciplinary, quantitative approach to develop effective strategies for integrating stocking into traditional fishery management, with an initial focus on red drum (Sciaenops ocellatus). With consensus from stakeholders, particularly from a well-informed advisory board, focus has shifted over the past 8 years from production-oriented stocking to an assessment-driven developmental approach. The goal is to develop and expand economically successful and ecologically sound stocking technology for rapidly replenishing depleted fish stocks in a multi-billion dollar (US) saltwater recreational fishing industry. Release-recapture experiments for red drum have been underway in Tampa Bay for 6 years. This research has involved replicate stratified releases of ∼ 4 million red drum hatchlings, which are identifiable via genetic testing. More than 20,000 red drum tissues have been tested. These were obtained from fishery-independent and dependent sampling and from an angler-return program,. Of these, approximately 3,000 specimens have been assigned to hatchery breeding pairs. Experimental results, especially those based on hatchery fish recruited to the recreational fishery, have provided managers with valuable information about size at release, release timing, release habitat, and post-release movement.

Optimizing Cost-Effectiveness of Size at Release in Stock Enhancement Programs

Abstract In this paper, we consider how size at release (SAR)−dependent survival of stocked fish can influence the cost-effectiveness of stocking strategies. Production costs for various sizes of juvenile fish were related to performance based on capture rates in a subsistence fishery in Kaneohe Bay on the island of Oahu, Hawaii. Using production cost data from a small-scale research hatchery, we examined the costs required to rear striped mullet Mugil cephalus to various stocking sizes. A spreadsheet cost model for marine shrimp aquaculture was adapted to striped mullet intensive culture techniques in Hawaii. Costs were calculated for the maturation, hatchery, and nursery phases of striped mullet production based on spawning protocols that reflected conservation of wild-stock genetic diversity. We identified the costs required to rear fingerlings to each of five consecutive size intervals, ranging from 45 to 130 mm total length (TL). Size-dependent postrelease mortality had a significant impact on the co...

Manipulations of Stocking Magnitude: Addressing Density-Dependence in a Juvenile Cohort of Common Snook (Centropomus undecimalis)

We released hatchery-reared juvenile common snook (Centropomus undecimalis) to test the effects of augmenting age-1 abundance by 100% (high augmentation, n = 2) vs 10% (low augmentation, n = 2) in estuarine creeks of southwestern Florida. We monitored in-creek abundance of age-1 snook 1 month before releases in May 2002 to estimate wild snook density and stocking magnitude. All sampling used seining standardized for effort, gear efficiency, and depletion removal. After releases, sampling continued for 1 year. After 1 month, creeks with high augmentation showed a 126% and 74% increase in total age-1 abundance, and low augmentation creeks a 6% increase and an 18% decrease. Total age-1 abundance declined during fall in all creeks, but by winter, abundance increased again, comparable to earlier levels (132% and 67% above the pre-release estimates in high augmented creeks and 8% and 5% in creeks with low augmentation). While overall density was elevated in both high augmentation creeks, hatchery-reared snook in one creek experienced a 64–85% loss within 1 month after release; loss of hatchery-reared or wild snook was negligible in other experimental creeks. Pre-release density was not a good predictor of creek productive capacity, suggesting variation in habitat production and localized recruitment. Further work is needed to understand inter-cohort density-dependent interactions, food chain responses, and variation in habitat productivity.

Evolving context and maturing science: Aquaculture-based enhancement and restoration enter the marine fisheries management toolbox

Aquaculture-based enhancement of marine fisheries includes sea ranching, stock enhancement, and restocking. A rapidly evolving context and maturing science base have effectively put these approaches into the fisheries management toolbox. Among the contextual factors are (1) a rapid expansion of captive breeding and domestication to new marine species, (2) fisheries governance systems that address the common dilemma, and (3) global environmental change impacts on coastal fisheries that increasingly call for active approaches to maintaining or increasing fisheries yields and ecosystem services. The science base of marine restocking, stock enhancement, and sea ranching continues to advance rapidly and has now reached a point where it is becoming possible to assess the likely contribution of such approaches to fisheries management goals prior to major investments being undertaken and to design enhancement programs effectively and responsibly where good potential is judged to exist. This signifies an important transition of marine fisheries enhancement from an exploratory, research-oriented endeavor to a tool in the fisheries management tool box.

Potentials and Limitations of Stock Enhancement in Marine Recreational Fisheries Systems: An Integrative Review of Florida's Red Drum Enhancement

In this study, an integrative review of the potential for stock enhancement is conducted to support desirable management outcomes in marine recreational fisheries, focusing on the Florida, USA, red drum fishery as a case study. Here, stock enhancement is implicitly seen as a way of simultaneously achieving both ecological objectives of sustained wild fish populations and socioeconomic objectives of high fishing effort and/or catch rates. However, the review suggests that a fundamental tradeoff remains between these objectives in the short-term because stocking of hatchery fish is likely to result in at least partial displacement of wild fish through biological interactions as well as increased fishing pressure. Contrary to the perception of enhancement as a “quick fix,” successful use of the approach in the marine recreational fishery is likely to require sophisticated stock management and some adaptation in governance. In developing the enhancement, it will be necessary to address uncertainty in key attributes, specifically dynamics of recruitment, angler-effort responses, and stakeholder involvement. This may be achieved by combining quantitative modeling, monitoring, and stocking experiments in an active adaptive management framework to consider enhancement in the context of alternative management strategies. It is suggested that any interim enhancement should minimize ecological risk per socioeconomic benefit by stocking larger fish in areas where high fishing mortality limits abundance of wild fish. These conclusions are largely generalizable to other recreational enhancements, and this work serves as a model of rarely published a priori enhancement evaluation.

Generalized Predatory Impact Model: A Numerical Approach for Assessing Trophic Limits to Hatchery Releases and Controlling Related Ecological Risks

Rigorous assessment of species and ecosystem biology underpins responsible marine stock enhancement. Estimation of limits to stocking density, based on ecosystem productivity and energetic requirements of stocked species, can be used to gauge the appropriate magnitude of release densities, minimizing waste of resources, and the possibility for adverse stocking effects. A generalized mass-balance model (generalized predatory impact model) for stocking density estimation has been developed. The approach is based around the principles of ECOPATH and accounts for dynamic estimation of stocking-related ecosystem relationships at fine temporal (days) and spatial scales. The main parameter inputs include probability distributions for key biological and life-history traits of stocked species and estimates of primary productivity for the target ecosystem. The energetic requirements of stocked fish are evaluated in terms of growth and mortality as well as ontogenetic transitions in diet, habitat use, morphology, and migration. The theoretical carrying capacity for a stocked species within a given arena is assessed from primary productivity, levels of predation by stocked fish on different trophic groups, and a specified level of acceptable trophic impact. A Monte Carlo analysis of uncertainty is used to provide a probability distribution of stocking densities for a given trophic impact. The model is applied for stocking juveniles of snook (Centropomus undecimalis) in Sarasota, FL, USA, and mulloway (Argyrosomus japonicus) in Georges River, NSW, Australia. The model is useful for estimating an appropriate stocking density when planning pilot-scale fish releases. Such releases should be carefully monitored to validate model assumptions and determine density-dependent and other environmental effects.

Introduction to a Special Section: Hatcheries and Management of Aquatic Resources (HaMAR)—Considerations for Use of Hatcheries and Hatchery-Origin Fish

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