Breathing life into fisheries stock assessments with citizen science

Citizen science offers a potentially cost-effective way for researchers to obtain large data sets over large spatial scales. However, it is not used widely to support biological data collection for fisheries stock assessments. Overfishing of demersal fishes along 1,000 km of the west Australian coast led to restrictive management to recover stocks. This diminished opportunities for scientists to cost-effectively monitor stock recovery via fishery-dependent sampling, particularly of the recreational fishing sector. As fishery-independent methods would be too expensive and logistically-challenging to implement, a citizen science program, Send us your skeletons (SUYS), was developed. SUYS asks recreational fishers to voluntarily donate fish skeletons of important species from their catch to allow biological data extraction by scientists to produce age structures and conduct stock assessment analyses. During SUYS, recreational fisher involvement, sample sizes and spatial and temporal coverage of samples have dramatically increased, while the collection cost per skeleton has declined substantially. SUYS is ensuring sampling objectives for stock assessments are achieved via fishery-dependent collection and reliable and timely scientific advice can be provided to managers. The program is also encouraging public ownership through involvement in the monitoring process, which can lead to greater acceptance of management decisions

Status of demersal finfish stocks on the west coast of Australia

Assessments of the key indicator species for the West Coast Demersal Scalefish Resource (WCDSR; West Australian dhufish Glaucosoma hebraicum, Snapper Pagrus auratus and Baldchin groper Choerodon rubescens) in 2007 and 2009 demonstrated that the stocks were experiencing overfishing. Thus, between late 2007 and early 2010, substantial changes were made to the management of the commercial and recreational fisheries that exploit the WCDSR. These were designed to reduce catches of the entire suite of demersal scalefish species (and of each indicator species) by both the commercial and recreational sectors in the West Coast Bioregion (WCB) by at least 50 % of the 2005/06 levels (the catch benchmark), to allow stocks to recover. The current (third) stock assessment of indicator species for the demersal scalefish suite was based on age data collected between 2008/09-2010/11 for G. hebraicum and P. auratus and 2007/08-2010/11 for C. rubescens and on catch statistics for the commercial and recreational fishing sectors (including charter fishing) from 2008-2012. The assessment compared estimates of fishing mortality (F) for the most recent period with several previous time periods and against internationally accepted biological reference points to determine whether there was evidence of any stock recovery. The sampling period for this assessment included the period when major changes were being made to management in the WCB of commercial and recreational/charter fishing for demersal species. As each of the indicator species is relatively long-lived, it is expected that it will take at least 10 years from these management changes before their stocks show strong signs of recovery, and that it may take substantially longer before they fully recover (~15-20 years). Catches of the demersal suite of species in the WCB by the commercial sector and of the top 15 species taken by the recreational sector have been reduced to less than the catch benchmark. Although catches of all indicator species have been reduced, those of two indicator species, P. auratus and C. rubescens, have not been reduced below the catch benchmark by all sectors

Rapid and cost-effective assessment of connectivity among assemblages of Choerodon rubescens (Labridae), using laser ablation ICP-MS of sagittal otoliths

A rapid and cost-effective assessment was required to provide advice to management on the connectivity between juvenile and adult life cycle stages of Baldchin Groper Choerodon rubescens, a labrid endemic to the west coast of Australia, which has high social value, but relatively low commercial fishery importance. To minimise costs we used laser ablation ICP-MS to analyse levels of a small suite of elements (Ca, Mg, Mn, Cu, Zn, Sr, Rb, Ba and Pb) at the margin (adult phase) and core (juvenile phase) of the same otoliths of adult C. rubescens, collected at ten locations in five management zones. The elemental composition of both otolith margins and cores differed significantly among management zones and in some cases among locations within zones. Similarity of the pattern of among-zone elemental composition in otolith margins and cores indicated that, when cores are laid down, individuals have already recruited to the zones they will occupy as adults and there is no evidence of discrete juvenile nurseries. Thus, movement of juvenile or adult C. rubescens is likely to occur at relatively small spatial scales. Monitoring and management of adult stocks at the management zone level may be appropriate to sustain stocks broadly, but may not detect more localised depletion. Methods of elemental analyses are discussed and costs and benefits of this study vs an equivalent tagging study were compared

Does a spatiotemporal closure to fishing Chrysophrys auratus (Sparidae) spawning aggregations also protect individuals during migration?

Understanding migration dynamics of fishes that aggregate-spawn is critical if spatiotemporal closures to fishing are expected to protect them. Concern over fishing of Chrysophrys auratus spawning aggregations in embayments near a west Australian city led to an annual 4-month spatial fishing closure. However, the extent to which it protects fish migrating to and from aggregations is unclear. Acoustic telemetry demonstrated a bimodal pattern of entry to and departure from the main embayment via only one of several pathways. Among years, 33%–56% of fish occurred in the pathway prior to the closure, but most left before it ceased. Fish were detected within the closure in multiple but not always consecutive years. Variation in migration timing and aggregation philopatry may alter capture risk, but pre- and postspawning migratory fish are fished in the main pathway and adjacent reefs, which would presumably impact spawning aggregation biomass. Assessment of this would assist in understanding whether expansion of the closure’s spatial and temporal limits is necessary to ensure spawning biomass or whether current management is sufficient

A comparison of the stock structures of two exploited demersal teleosts, employing complementary methods of otolith element analysis

Complementary methods of otolith element analysis (IRMS of stable isotopes and laser ablation ICP-MS of trace elements) were used to elucidate the stock structures in Western Australia of the exploited demersal West Australian dhufish Glaucosoma hebraicum and Snapper Pagrus auratus. Residency of adults during their most recent part of life and the existence of important nursery locations were investigated by analysing otolith margins and cores, respectively, to evaluate the applicability of current spatial management. Stable oxygen isotope ratios (18O/16O) in both margins and cores of G. hebraicum otoliths increased with latitude and thus decreasing mean annual water temperature. Analyses of δ18O, stable isotope composition (SI; δ18O, δ13C) and trace element composition (TE; 25Mg, 88Sr, 138Ba) in otolith margins of G. hebraicum from four management areas on the west coast of Australia indicated that adults were resident in each area. Analyses of elements in otolith cores demonstrated that, by the early juvenile stage (< 1 year old), individuals will have recruited to the area where they will remain as adults. Analyses of δ18O and both SI and TE compositions in otolith margins of adult P. auratus indicated residency within each of three large bioregions (Gascoyne, GCB; West, WCB; South, SCB) along the west and south coasts of western Australia. As for G. hebraicum, the data also demonstrated residency at the finer scale, i.e. within the four management areas on the west coast. The lack of a conspicuous pattern in δ18O levels in P. auratus otolith cores implied that adults in each area recruited from a range of nurseries. Although both SI and TE composition demonstrated that there was substantial self-recruitment within the WCB and SCB and within two of the four areas of the WCB, stock(s) of P. auratus at the southern extent of the GCB are likely to be partially reliant on immigration. Elemental signatures in otoliths of G. hebraicum and P. auratus demonstrated that adults in each management area of the WCB could be treated as separate stocks. However, while recruitment of juvenile G. hebraicum to adult stocks would occur primarily from adjacent multiple nurseries within areas of the WCB, adult P. auratus in any one bioregion and at least two of the four areas within the WCB were derived from a range of nurseries, including across area and bioregion boundaries