Crabs of the subfamily Sesarminae are important components of mangrove ecosystems in the Indo-west Pacific, Africa, the Caribbean and South America. By retaining a large proportion of mangrove leaf-litter within mangrove forests, they profoundly influence the functioning of mangrove ecosystems. Despite obvious importance to ecosystem functioning, little is known about predation on sesarmid crabs. Three large, predatory fishes of tropical lndo-Pacific estuaries, the groupers Epinephelus coioides and E. malabaricus and the snapper Lutjanus argentimaculatus are known to feed on brachyuran crabs. However, the contribution of sesarmids to the brachyuran component of the diets of these fishes is unknown. To determine the extent to which these fishes prey on sesarmid crabs, the gut contents and stable isotope values (613C and 615N) of E. coioides, E. malabaricus, and L. argentimaculatus from 3 mangrove estuary systems on the northeast coast of tropical Australia were investigated. All 3 species fed extensively on sesarmid crabs. Sesarmid crabs were the dominant food items for E. malabaricus and L. argentimaculatus, occurring in 50% of the stomachs that contained prey, and being the most common prey in terms of overall numbers. Although still the dominant prey, sesarmids occurred in only 30% of E. coioides stomachs. As well as being numerically dominant, sesarmids were large relative to other prey types. The 3 species also had stable isotope values enriched by about +0.75 to + 2 6I3C and +1.5 to +2.5 6I5N, which were also consistent with extensive feeding on these crabs. Most other sympatric species had quite u f e r e n t diets and stable isotope profiles. Extensive feeding on sesarmid crabs by these fishes has a range of implications for the ecology of tropical mangrove ecosystems. Food webs are apparently more complex, and food chains leading from mangroves to top predators may be shorter than previously thought. Furthermore, a substantial part of the mangrove productivity sequestered by sesarmid crabs may be exported from mangrove ecosystems as a result of offshore migration by these fishes. The low incidence of piscivory in these fishes adds support to theories that reduced predation pressure may enhance the nursery ground value of tropical mangrove systems for fishes.Published June 26

page 409 Introduction 410 Stock enhancement 412 Reasons for the lack of success in previous attempts at stock enhancement 413 A way forward 417 A flow-chart for the scientific evaluation of stock enhancement proposals 418 Criticisms of the Flow-Chart model 425 The role of aquaculture in the future of stock enhancement 425 Conclusion 426 Acknowledgements 426 References 426Abstract Stock enhancement has been viewed as a positive fisheries management tool for over 100 years. However, decisions to undertake such activities in the past have often been technology-based, i.e., driven by the ability to produce fishes, with most stock enhancement projects having limited or no demonstrated success. The reasons for this have been due to an inability to identify and/or control the underlying reasons why a fishery is under-performing or not meeting management objectives. Further, stock enhancement has often been applied in isolation from other fisheries management tools (e.g., effort control). To address these issues and consider stock enhancement in a broader ecosystem perspective, a new approach for stock enhancement is proposed. The proposed model comprises four major steps; a review of all information about an ecosystem/fishery/stock and the setting of clear management targets; a comparison of all relevant fisheries management tools with the potential to meet the management targets; the instigation of a scientifically based, pilot-scale, stock enhancement program with clear objectives, targets, and evaluations; and a fullscale stock enhancement program if the pilot project meets the objectives. The model uses a flow-chart that highlights a broad range of scientific and other information, and the decisions that need to be made in relation to stock enhancement and fisheries management in general. In this way all steps are transparent and all stakeholders (managers, scientists, extractive and non-extractive users, and the general public) can contribute to the information collection and decision making processes. If stock enhancement is subsequently identified as the most-appropriate tool, then the stepwise progression will provide the best possible chance of a positive outcome for a stock enhancement project, while minimizing risks and costs. In this way, stock enhancement may advance as a science and develop as a useful fisheries management tool in appropriate situations.

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Wakefield, C. B., Newman, S. J., and Molony, B. W. 2010. Age-based demography and reproduction of hapuku, Polyprion oxygeneios, from the south coast of Western Australia: implications for management. – ICES Journal of Marine Science, 67: 1164–1174. The hapuku, Polyprion oxygeneios, inhabits deep (>100 m) continental slope waters of Western Australia. In all, 1352 P. oxygeneios were collected from the waters along the south coast of Western Australia (ca. 35°S) from 2004 to 2008. The species is gonochoristic, and spawns during the austral winter (May–September). Ages were estimated from counts of opaque zones from thin-sectioned sagittal otoliths. Classification analysis of the outer margin of sectioned otoliths indicated that a single opaque zone is deposited annually. Female P. oxygeneios (n = 630; 535–1114 mm total length, TL) ranged in age from 2 to 35 years and males (n = 691; 521–1004 mm TL) from 2 to 52 years. von Bertalanffy growth models for male and female P. oxygeneios were statistically, but not biologically, different (<5% difference in mean and estimated lengths-at-age). Estimates of the lengths and ages at which 50% of the females and males in the population reached sexual maturity were 760 and 702 mm TL and 7.1 and 6.8 years. The instantaneous rate of natural mortality (M) was estimated to be 0.09. Estimates of the instantaneous rate of fishing mortality (F) were low (0.01–0.05). Harvest rates in 2005 and 2006 were close to estimated sustainable levels. Monitoring of any future increases in catch and effort in continental slope waters in both State- and Commonwealth-managed fisheries is required in order to assess impacts to stock sustainability. Sustainable management would also benefit from improved understanding of possible pan-oceanic recruitment of the species among southern hemisphere populations.

page 409 Introduction 410 Stock enhancement 412 Reasons for the lack of success in previous attempts at stock enhancement 413 A way forward 417 A flow-chart for the scientific evaluation of stock enhancement proposals 418 Criticisms of the Flow-Chart model 425 The role of aquaculture in the future of stock enhancement 425 Conclusion 426 Acknowledgements 426 References 426Abstract Stock enhancement has been viewed as a positive fisheries management tool for over 100 years. However, decisions to undertake such activities in the past have often been technology-based, i.e., driven by the ability to produce fishes, with most stock enhancement projects having limited or no demonstrated success. The reasons for this have been due to an inability to identify and/or control the underlying reasons why a fishery is under-performing or not meeting management objectives. Further, stock enhancement has often been applied in isolation from other fisheries management tools (e.g., effort control). To address these issues and consider stock enhancement in a broader ecosystem perspective, a new approach for stock enhancement is proposed. The proposed model comprises four major steps; a review of all information about an ecosystem/fishery/stock and the setting of clear management targets; a comparison of all relevant fisheries management tools with the potential to meet the management targets; the instigation of a scientifically based, pilot-scale, stock enhancement program with clear objectives, targets, and evaluations; and a fullscale stock enhancement program if the pilot project meets the objectives. The model uses a flow-chart that highlights a broad range of scientific and other information, and the decisions that need to be made in relation to stock enhancement and fisheries management in general. In this way all steps are transparent and all stakeholders (managers, scientists, extractive and non-extractive users, and the general public) can contribute to the information collection and decision making processes. If stock enhancement is subsequently identified as the most-appropriate tool, then the stepwise progression will provide the best possible chance of a positive outcome for a stock enhancement project, while minimizing risks and costs. In this way, stock enhancement may advance as a science and develop as a useful fisheries management tool in appropriate situations.