Gary Jackson

Stock enhancement as a fisheries management tool

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 full-scale 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.

Spatial variation in life history characteristics of snapper (Pagrus auratus) within Shark Bay, Western Australia

Abstract Life history characteristics of snapper (Pagrus auratus) were found to vary at fine spatial scales (less than tens of kilometres) in the sub-tropical waters of Shark Bay, Western Australia, from research undertaken between 1997 and 2004. Differences in the timing and duration of the spawning season, length and age at maturity, and maximum age and growth between snapper from the Eastern Gulf, Denham Sound and Freycinet Estuary were attributed to spatial differences in environmental conditions and density-dependent responses to fishing-induced changes in spawning biomass. Such fine-scale spatial variation in the biological characteristics of snapper is consistent with results of previous stock identification studies and further supports the geographic scale at which local snapper stocks are managed to protect both stock productivity and genetic diversity.

Science behind management of Shark Bay and Florida Bay, two P-limited subtropical systems with different climatology and human pressures

This special issue on ‘Science for the management of subtropical embayments: examples from Shark Bay and Florida Bay’ is a valuable compilation of individual research outcomes from Florida Bay and Shark Bay from the past decade and addresses gaps in our scientific knowledge base in Shark Bay especially. Yet the compilation also demonstrates excellent research that is poorly integrated, and driven by interests and issues that do not necessarily lead to a more integrated stewardship of the marine natural values of either Shark Bay or Florida Bay. Here we describe the status of our current knowledge, introduce the valuable extension of the current knowledge through the papers in this issue and then suggest some future directions. For management, there is a need for a multidisciplinary international science program that focusses research on the ecological resilience of Shark Bay and Florida Bay, the effect of interactions between physical environmental drivers and biological control through behavioural and trophic interactions, and all under increased anthropogenic stressors. Shark Bay offers a ‘pristine template’ for this scale of study.

Long-term monitoring of boat-based recreational fishing in Shark Bay, Western Australia: providing scientific advice for sustainable management in a World Heritage Area.

Effective management of a recreational fishery must include long-term monitoring programs that allow determination of trends in temporal and spatial variability of catch and effort data. Such monitoring becomes of inherently greater importance when managing a recreational fishery in a World Heritage Area, such as Shark Bay, Western Australia. Between 1998 and 2010, 11 12-month bus-route surveys of boat-based recreational fishing were undertaken at three key boat ramps in Shark Bay. These surveys demonstrated that, in response to the progressive implementation of new management measures, the estimated annual recreational fishing-boat effort decreased by 46%. As a consequence, the estimated annual retained and released catches of the key species, pink snapper (Pagrus auratus), declined and the proportions of the catches of this species that were released each year increased. Annual catches of other species also declined, however, the composition of species retained and released each year varied. The study demonstrated that monitoring of the recreational fishery within Shark Bay provided both immediate and longer-term data on the responses by recreational fishers to changes in management. This produced the information necessary to assess the effectiveness of management measures that were introduced and to modify these as required.

Tagging studies reveal restricted movement of snapper (Pagrus auratus) within Shark Bay, supporting fine-scale fisheries management

The snapper (Pagrus auratus) fisheries of Shark Bay’s complex inner gulfs are managed on a fine spatial scale (tens of kilometres). Following the splitting of the Western Gulf into two management zones, results from an earlier 1980s tagging study were revisited to assess the suitability of management arrangements. Recaptures up to 15 years at liberty showed highly restricted movement, with 300 of 491 occurring within 5 nautical miles of the tagging site and only 3.3% crossing the new zone boundary. A simple stock-trajectory model simulating the two Western Gulf populations demonstrated a negligible impact from a 1% per annum level of mixing. The 1980s study was repeated between 1998 and 2003 by tagging 2558 snapper, mainly in areas previously under-represented. Recaptures up to 2 years at liberty again showed highly restricted movement, with 181 of 197 recaptures occurring at the tagging site. Juveniles were more sedentary than adults, the latter showing limited evidence of inter-annual spawning-site fidelity. Together, both studies support the use of three small management zones. Community acceptance of these complex arrangements was aided by collaborating with volunteers on research programs, which improved their understanding of the population structure.

Recovery of inner Shark Bay snapper (Pagrus auratus) stocks: relevant research and adaptive recreational fisheries management in a World Heritage Property

Despite the increasing importance of marine recreational fishing, recreational fisheries management is often hampered by lack of adequate data and limited effectiveness of conventional regulations. In Shark Bay, Western Australia, snapper (Pagrus auratus) in the Eastern Gulf, Denham Sound and Freycinet Estuary have been a major attraction for recreational fishers since the 1960s. Various management measures were progressively introduced from 1998 onwards to limit snapper catches, including increases in minimum length, introduction of a maximum length, reductions in daily bag limit, a moratorium in the Eastern Gulf (June 1998–March 2003), a 6-week spawning closure in the Freycinet Estuary and, finally, the introduction of a Total-Allowable-Catch-based system in 2003. Stock assessments in 2011 indicated that spawning biomass in the Eastern Gulf and Denham Sound had rebuilt to the management target level while biomass in the Freycinet Estuary remained below the threshold level but was continuing to slowly rebuild. This paper summarising the research and adaptive management of the snapper fishery over the last 15+ years represents an important case study that addresses a range of issues typically associated with marine recreational fisheries, including assessment of stock size and recreational catch, evaluation of management regulations and active engagement with the recreational fishing community.

Real‐time PCR validation of visually identified snapper Chrysophrys auratus (Sparidae) eggs

In this study, a total of 212 eggs were visually identified as snapper Chrysophrys auratus. Real-time PCR confirmed visual identification in 69% of cases but corroboration varied widely among plankton samples. The use of molecular tools to support visual identification prior to adopting daily egg production stock assessment methods should be considered.

Accepting final counts from repeat readings of otoliths: should a common criterion apply to the age estimation of fish?

Multiple readings of otoliths are often carried out to assess the repeatability and reliability of increment counts for estimating fish age. Various criteria have been used to assign or discard age estimates from repeated counts when discrepancies occur although the reasons for doing so are usually not stated or justified. Trends in relative frequencies (percentage disagreement, PD) and magnitudes (inter-read discrepancy, IRD) of otolith-count discrepancies were explored for 15 species of fish collected from a range of locations around Australia to explore generality in the best explanatory model(s) for otolith-count discrepancies and, hence, the most appropriate criterion for accepting or rejecting age estimates from multiple-count data. Increasing discrepancies with increasing age, according to a constant per-increment probability of error, was the best-approximating model for 9 of the 15 species for PD data but for only two species for IRD data. Our results indicated disproportionately higher rates of rejection of estimates from older age groups if exact agreement between repeated counts was required for age acceptance. Results varied with the reader, region and the method of otolith reading, indicating that multiple criteria for accepting or rejecting counts from multiple readings may be required among or even within species.

Isolation and characterisation of 16 polymorphic microsatellite loci for bight redfish, Centroberyx gerrardi (Actinopterygii : Berycidae), and cross-amplification in two other Centroberyx species

Abstract. Bight redfish, Centroberyx gerrardi, is a demersal teleost endemic to continental shelf and upper slope waters of southern Australia. Throughout most of its range, C. gerrardi is targeted by a number of separately managed commercial and recreational fisheries across several jurisdictions. However, it is currently unknown whether stock assessments and management for this shared resource are being conducted at appropriate spatial scales, thereby requiring knowledge of population structure and connectivity. To investigate population structure and connectivity, we developed 16 new polymorphic microsatellite markers using 454 shotgun sequencing. Two to 15 alleles per locus were detected. There was no evidence of linkage disequilibrium between pairs of loci and all loci except one were in Hardy–Weinberg equilibrium. Cross-amplification trials in the congeneric C. australis and C. lineatus revealed that 11 and 16 loci are potentially useful, respectively. However, deviations from Hardy–Weinberg equilibrium and linkage disequilibrium between pairs of loci were detected at several of the 16 markers for C. australis, and therefore the number of markers useful for population genetic analyses with C. lineatus is likely considerably lower than 11.