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The Shark Bay trawl fishery is Western Australia's most valuable prawn fishery (worth AUD$25 million in 2014). The 18-vessel fleet targets western king prawns ( Penaeus latisulcatus ), brown tiger prawns ( P. esculentus ) and also retains saucer scallops ( Ylistrum balloti ) and blue swimmer crabs ( Portunus armatus ). Increased fuel prices, falling prawn prices and lower catches of other species, following extreme environmental events, have impacted fishery profits. A biomass dynamics model with an economic component indicated that total revenue levels start to decline when annual effort increases beyond ~ 200 fishing days per boat. Annual effort required to achieve MEY, when based solely on prawn fishing, is 115–150 days per boat after accounting for fixed and variable fishing costs and annual fishing efficiency increases of 1–2%. From 2007–2014, the adjusted effort was 188–192 days per boat. Fishing occurred between March and November during 7–8 fishing periods, separated by 5–8 day (low catchability) moon closure periods. An empirical daily profit assessment (2007–2015), accounting for recruitment variation, daily prawn size compositions, monthly market prices for different prawn species and sizes, and daily fishing costs, showed vessels made profits on ~ 115–160 days and losses on ~ 15–55 days per year, when fishing occurred near the full moon. The fishery benefitted in 2013–2015 by starting later in the year and better targeting within-season effort. This management strategy within the effort-control framework, which improved profitability, maintained higher spawning stocks and reduced ecosystem fishing impacts, has wider application in prawn fishery management.

The cover of seagrasses and macroalgae, landings and fishery-independent measures of spawning stock and recruitment for brown tiger prawns, were monitored immediately following a major cyclone in Exmouth Gulf, Western Australia in March 1999. Anecdotal evidence on the extent of seagrass from 1990 to 1998 suggests that the cyclone caused a major, immediate disruption and loss of the seagrass/macroalgal beds (to ≤2% cover), the critical prawn nursery habitat, and mangroves in the shallow inshore waters of the system. Prawn landings and recruitment to the fishery were not affected in the year of the cyclone, but were markedly lower in the two years immediately afterwards and then increased as the cover of macrophytes increased to over 40% in 2003. Tiger prawn landings and catch rates were not affected in Shark Bay, a system 500 km south of Exmouth Gulf that did not experience cyclonic disturbance. Seagrasses in Exmouth Gulf showed a succession of species from small colonising species (Halophila ovalis and Halodule uninervis) to larger, broad-leaved species (Cymodocea serrulata, Syringodium isoetifolium) only two years after the cyclone. The recruitment and landings of tiger prawns were correlated significantly with the total cover of macroalgae and seagrass. The large loss of seagrass and macroalgae reduced the settling habitat for postlarvae and the nursery habitat for juvenile tiger prawns, probably leading to the lower recruitment to the fishery. These findings suggest that the extent of seagrass and macroalgae are some of the factors defining the productivity of the tiger prawn fishery in Exmouth Gulf.

Creating large conservation zones in remote areas, with less intense stakeholder overlap and limited environmental information, requires periodic review to ensure zonation mitigates primary threats and fill gaps in representation, while achieving conservation targets. Follow-up reviews can utilise improved methods and data, potentially identifying new planning options yielding a desirable balance between stakeholder interests. This research explored a marine zoning system in north-west Australia–a biodiverse area with poorly documented biota. Although remote, it is economically significant (i.e. petroleum extraction and fishing). Stakeholder engagement was used to source the best available biodiversity and socio-economic data and advanced spatial analyses produced 765 high resolution data layers, including 674 species distributions representing 119 families. Gap analysis revealed the current proposed zoning system as inadequate, with 98.2% of species below the Convention on Biological Diversity 10% representation targets. A systematic conservation planning algorithm Maxan provided zoning options to meet representation targets while balancing this with industry interests. Resulting scenarios revealed that conservation targets could be met with minimal impacts on petroleum and fishing industries, with estimated losses of 4.9% and 7.2% respectively. The approach addressed important knowledge gaps and provided a powerful and transparent method to reconcile industry interests with marine conservation.

Saucer scallops, Amusium balloti, are targeted by Shark Bay prawn and scallop trawl fisheries where regulatory discarding can occur during summer and winter months that may adversely impact the recruitment of this resource. Survival of repeatedly discarded saucer scallops was thus estimated for the Shark Bay trawl fisheries using short-term tag—recapture experiments under various fishing and environmental conditions. Estimates of apparent survival of discarded scallops was significantly higher during the postspawning winter period (>90%) than during the prespawning summer period (20–90%), but no differences in survival between fishing grounds or between postcapture treatment groups (air exposed vs. those kept in a holding tank) were observed. This suggests that thermal stress from large differences in seasonal temperatures was more critical to scallop survival than differences in scallop reproductive condition. Thus past (pre-2004) management regulations that imposed regulatory discarding during ...

The present paper is the first description using geostatistical modelling of recruitment (0+) and residual (1+) scallop variability from an annual survey in a semi-tropical embayment. Geostatistical modelling provides a useful tool to explore and interpret distribution patterns and can provide information to determine potential behaviour of fishers. It may also aid in determining the time it will take from the beginning of the season to reach a catch-rate threshold, which is the management strategy implemented in the Shark Bay scallop fishery since 2004. High variability in recruit abundance and spatial distribution was observed among years, whereas patterns of residual abundance and distribution were less variable because of the fishing patterns of both the scallop and prawn fleets. Comparisons of commercial catch patterns indicated that high survey-abundance areas correlate with higher catches, validating that survey results are a good tool for fishers to utilise to target their fishing practices to optimise and maximise catch efficiencies. The study highlighted the inherent annual variability of scallop recruitment abundance and distribution that are primarily considered to be environmentally driven. However, both recruits and residual scallops contribute to the whole catch, so retaining residual scallops from year to year is important.

The performance of square-mesh codends (as opposed to the conventional diamond mesh) was examined as a discard and by-catch reduction device for the Shark Bay saucer-scallop trawl fishery. Of the three different-sized square-mesh codends (50, 55, 60 mm) tested against the standard 100-mm diamond-mesh codend, the 50-mm square-mesh codend performed poorly with relatively high retention of small (

Stock assessments to support sustainable management in data-limited fisheries present a challenge to fisheries scientists and managers. This is the case with the Shark Bay Crab Fishery, which has expanded rapidly in the past 10 years, to become Australia’s highest-producing blue swimmer crab fishery. The resource is harvested commercially by two sectors, the Shark Bay crab trap and trawl fisheries (combined catch of ~800 t), as well as supporting a small but important recreational fishery. Commercial catch and effort data have been collected for the fishery since the early 1980s, commercial trap-monitoring data since 1999, and fishery-independent trawl-survey data since 2001. There is conflicting evidence on the impact that significant increases in catch and effort over the past decade has made on this fishery, such as legal catch rates remaining relatively constant, but declines occurring in the abundance of large crabs. There has also been concern over the level of latent effort in the fishery, with the trap sector currently operating at 70–80% of its potential effort and the capacity for further increases in crab landings by the trawl fleet. Since July 2011, the relative abundance of all size classes of crabs declined significantly. The reasons for this unexpected decline are yet to be understood, but are likely to be linked to adverse environmental extremes (flooding and very warm water temperatures) during the summer of 2010–2011, associated with a very strong La Niňa event. Preliminary assessment indicated that the spawning stock that led to the low recruitment was within historic ranges. The current challenge for the research and management of this fishery is to clarify the causes for this recent decline, and establish suitable biological indicators that will determine the appropriate level of catch and harvest strategy to ensure the future sustainability of the stock.