Western Rock Lobster Research Articles

Spiny lobster recreational fisheries in Australia and New Zealand: An overview of regulations, monitoring, assessment and management

Spiny (rock) lobsters occur globally and, although harvest is dominated by commercial fisheries, it is important to account for recreational harvest in stock assessments and fisheries management. This paper provides a contemporary review of recreational fishing for five spiny lobster species in Australia and New Zealand. Each jurisdiction has established approaches for collecting data which best meet their information needs (telephone-diary or telephone-recall surveys, charter logbooks, tag reporting). Jurisdictions with specific spiny lobster licences (Western Australia, Tasmania) or mandatory reporting (charter logbooks in Western Australia, tag reporting in Victoria) use these registers as a sampling frame for annual reporting of participation, fishing effort, catch (numbers) and harvest (tonnes). All other jurisdictions use a general fishing licence or general population sampling frame for telephone-diary surveys to provide periodic reporting of catch and harvest. Annual participation in spiny lobster recreational fishing was highest in Western Australia (35,236 ± SE 626 fishers in 2022–23), followed by Tasmania (13,715 ± SE 1067 fishers in 2022–23) and Victoria (5516 fishers in 2020–21). Annual recreational harvest of all spiny lobster species, combined for the most recent data collection period in each jurisdiction, was 830 tonnes; consisting mostly of Western Rock Lobster (Panulirus cygnus) from Western Australia and Southern Rock Lobster (Jasus edwardsii) from Tasmania and New Zealand. This review illustrates the various spatial scales of monitoring, reporting and assessment in each jurisdiction. All monitoring provides information on catch and harvest, with some also reporting participation, effort, carapace length and non-catch related variables. The designs underlying these approaches vary from probability-based (opt-out) and census (mandatory), and it is important to understand the benefits and inherent biases of each. Understanding the parallels between jurisdictions offers valuable insights into how to cost-effectively monitor spiny lobster recreational fisheries and integrate this data into stock assessment and harvest strategies to support sustainable fisheries into the future.

Microplastic extraction from digestive tracts of large decapods

The reliable quantification of microplastic contamination in chitinous organisms requires validated methods to remove interfering complex organic and inorganic material. This study trialled KOH, H2O2 and HNO3 digestion methods on the digestive tracts of two large decapods (Panulirus cygnus and Portunus armatus) to validate a protocol that facilitates reliable microplastic extraction. KOH digestion provided the best recovery (>95 %) of all polymers (e.g. polyamide, polyethylene, polyethylene terephthalate, polypropylene, polystyrene and polyvinyl chloride), with the lowest impact to their physical morphology and chemical spectra. While HNO3, and HNO3 + H2O2 treatments were more effective at digesting chitin, they destroyed polyamide, and altered several other polymers. High digestion efficiency did not result in high matrix clarification or high microplastic recovery for large decapods. This study emphasises the importance of validating species-specific microplastic extraction methods, whilst proposing additional post-digestion protocols, such as density separation, for complex samples, that can be applied in future research investigating plastic contamination in large decapods.

Observations of the association by early-juvenile western rock lobsterPanulirus cygnuswith seagrass assemblages (Decapoda: Achelata: Palinuridae)

AbstractThe fishery of the western rock lobster, Panulirus cygnusGeorge, 1962, is Australia’s most valuable wild-caught single-species fishery. Recruitment in some regions of the fishery was observed to be significantly lower than expected after the 2010/2011 West Australian marine heatwave that caused extensive disturbance of dominant coastal habitats. This event generated interest in the study of the factors influencing survival and recruitment of post-larval benthic P. cygnus after settlement. The habitat associations of the highly cryptic post-settlement early-juveniles were previously unknown, with only anecdotal observations of individuals within limestone crevices in nearshore habitats. Our study used early-juveniles derived from ongoing monitoring of puerulus settlement to examine their habitat association mechanism in mesocosm experiments. Comparison of common nearshore habitat assemblages (bare sand, limestone crevices, and seagrasses (Posidonia and Amphibolis) at varying seagrass densities) found that most early-juveniles associated strongly with Amphibolis assemblages at high stem densities (~2,100 stems m–2). A shift in association between Amphibolis fronds and stems at high stem density to Amphibolis-shaded sand and leaf debris at low stem density indicated active habitat selection by early-juveniles. Habitat choices were tested with the scents of prey items and habitat types within Amphibolis assemblages using Y-maze bioassays. No significant olfactory choices were found, suggesting that habitat associations may be driven by multiple cues. Our study provides new laboratory-based insights into the habitat association of early-juvenile P. cygnus and suggests changes in seagrass assemblage identity and density are likely to be important. Further experimentation is needed to define the cues driving these patterns. The impact of habitat change on recruitment in this important fishery remains unknown and should be an objective of future research.

Fine-scale variability in catch and growth rates of western rock lobsters (

Context The western rock lobster fishery is recognised to be conservatively managed, with breeding stock levels estimated to be at record levels over the past decade. Despite this, anecdotal reports from commercial fishers identified an area of unexpectedly low catches in the centre of the fishery and lobsters’ biogeographic distribution. Aim To confirm the presence of this suspected ‘low-catch’ zone and examine the variability in catch and growth rates of lobsters if identified. Methods This study conducted an intensive mark–recapture survey over 8 months to explore catch rate, density, movement and growth rates across this ‘low-catch’ zone and three comparable locations. Key results In total, 9318 lobsters were caught and 7565 individuals were tagged during the study. Consistently low catch rates of under-sized lobsters were observed in the ‘low-catch’ zone, with catch rates increasing with distance from the zone. By contrast, similar catch rates of legal-sized lobsters were observed across all locations. Conclusions The study confirmed low catch rates, for under-sized lobsters, within an area of perceived low catch rates within the centre of the fishery. The lack of difference found in legal-sized catch rates among locations is likely to be due to the low fishing pressure in the ‘low-catch’ zone, resulting from hyperstability of fishers adapting to the historical perceived low catch rate. Modelled data demonstrated the ‘low-catch’ zone to be associated with faster growth rates and high fine-scale migration, indicating a potential release from density-dependent processes. Implications We anticipate that these results will be a useful starting point for future research into the mechanisms responsible for the unexpectedly low catch of sublegal lobsters within the ‘low-catch’ zone and the implications it may have on the wider population, both regionally and across the species distribution.

Recreational fishing pressure impacts the density and behaviour of the western rock lobster (Panulirus cygnus, George): evidence from small, no-take marine reserves

Abstract It is unknown whether lobster behaviour is sensitive to fishing, as has been previously suggested for fish. This study investigated the impacts of recreational fishing on the wariness of western rock lobster (Panulirus cygnus, George) through comparisons between fished sites and no-take reserves (NTRs) at Rottnest Island. We used visual census to survey the density and size structure of lobster at sites inside and outside three comparable NTRs, and baited remote underwater video to study the behaviour of lobster at comparable sites. The density of legal-sized P. cygnus was twice as high within NTRs (0.34 ± 0.05) than fished sites (0.16 ± 0.03). P. cygnus also spent less time with bait in fished sites (0.42 ± 0.15 min) than NTRs (1.15 ± 0.28 min). This study provides the first evidence that behaviour of decapods, namely P. cygnus, is sensitive to noninjury-related disturbance associated with recreational fishing, with higher wariness in fished areas. Investigation is required into potentially confounding biotic and abiotic factors to further explore the applicability of lobster wariness as an indicator for fishing pressure.

Improving design-based estimates of biological data collected from a restricted spatio-temporal access point survey of recreational fishers

Accurate and precise estimates of recreational harvest are required where there are formal catch allocations between commercial and recreational sectors. Yet they are challenging to obtain without appropriately designed surveys, especially in the recreational sector, which often require complex survey designs. Estimates of mean body mass are required for recreational fisheries when converting catch by numbers to catch by weight and should account for pseudoreplication to truly represent the characteristics of the data. However, methods for determining mean mass from recreational fishing surveys are rarely defined, leading to assumptions that an arithmetic mean has been applied, which does not account for pseudoreplication or hierarchical, clustered sampling. This study uses western rock lobster (Panulirus cygnus), commonly targeted by recreational fishers in Western Australia, as a case study to determine a mean mass for retained lobsters using several survey design-based methods. The six-year, restricted spatio-temporal access point survey of boat-based recreational fishers, who target lobsters by trapping or diving, addresses pseudoreplication by aggregating survey data and calculating a weighted mean and uncertainty for non-normally distributed data using nonparametric hierarchical bootstrapping. While we present the mean and confidence intervals for all levels of the survey design, our preferred level is the ultimate sampling unit (lobster) because there are insufficient replicates to conduct nonparametric hierarchical bootstrapping at the primary (day) or secondary (interview) sampling units. For this species, we recommend using a fishing method-based mean rather than an overall mean to capture annual variability in catch and participation and provide an index for determining harvest when catches by number are known for each fishing method. This approach for analyzing recreational fishing data is relevant to other fisheries estimating total recreational harvest from restricted spatio-temporal surveys.

Chemotaxis is important for fine scale habitat selection of early juvenile Panulirus cygnus

The western rock lobster (Panulirus cygnus [George 1962]) is the basis for Australia's most valuable single species wild caught fishery. The ability of early juvenile western rock lobster to select and settle onto suitable habitats is critical for the recruitment of this commercially important species. Many marine organisms, including the western rock lobster, have highly complex olfactory systems that allow for various behaviours including habitat selection and the location of food. We tested the active habitat selection of early juvenile western rock lobsters using only chemotaxis in scent based trials. We used a Y-maze bio-assay with which we were able to present individuals with several different natural scent stimuli. This study used three commonly observed broad habitat complexes followed by three fine scale seagrass assemblages to provide different scent stimuli. Seagrass habitats were chosen significantly more often by the juvenile lobsters in the broad habitat scale trials over bare sand and turf habitats. At a finer scale, lobsters showed a mixed response but tended to choose the canopy forming seagrass species, Amphibolis antarctica [(Labillardière) Sonder & Ascherson ex Ascherson, 1868] and Posidonia australis [Hooker, 1858] significantly more often than the other scents provided. This study developed a Y-maze chemotaxis assay for P. cygnus and confirmed that they respond to habitat related scent cues. These findings suggest the importance of seagrass habitats to early juvenile western rock lobsters and the potential impacts that habitat change may have on the successful recruitment of this commercially important species.

Using an oceanographic model to investigate the mystery of the missing puerulus

Abstract. Dynamics of ocean boundary currents and associated shelf processes can influence onshore and offshore water transport, critically impacting marine organisms that release long-lived pelagic larvae into the water column. The western rock lobster, Panulirus cygnus, endemic to Western Australia, is the basis of Australia's most valuable wild-caught commercial fishery. After hatching, western rock lobster larvae (phyllosoma) spend up to 11 months in offshore waters before ocean currents and their ability to swim transports them back to the coast. The abundance of western rock lobster post-larvae (puerulus) provides a puerulus index used by fishery managers as a predictor of lobster abundance 3–4 years later. This index has historically been positively correlated with the strength of the Leeuwin Current. In 2008 and 2009, the Leeuwin Current was strong, yet a settlement failure occurred throughout the fishery, prompting management changes and a rethinking of environmental factors associated with their settlement. Thus, understanding factors that may have been responsible for the settlement failure is essential for fishery management. Oceanographic parameters likely to influence puerulus settlement were derived for 17 years to investigate correlations. Analysis indicated that puerulus settlement at adjacent monitoring sites has similar oceanographic forcing, with kinetic energy in the offshore and the strength of the Leeuwin Current being key factors. Settlement failure years were synonymous with “hiatus” conditions in the southeast Indian Ocean and periods of sustained cooler water present offshore. Post-2009, there has been an unusual but consistent increase in the Leeuwin Current during the early summer months, with a matching decrease in the Capes Current, which may explain an observed settlement timing mismatch compared to historical data. Our study has revealed that a culmination of these conditions likely led to the recruitment failure and subsequent changes in puerulus settlement patterns.

Development of an individual-based tag recapture model to benchmark biomass and harvest rates in an iconic lobster fishery

The West Coast Rock Lobster Managed Fishery (WCRLMF) moved from input to output controls in 2010. This change affected the relativity of fishery-based data sources (e.g., catch rates and landed size composition), making the assessment of the fishery problematic. A novel examination of the stock dynamics was required to ensure the robustness of the stock assessment and associated management arrangements. This study derived estimates of current biomass levels and harvest rates from the release of over 60,000 tagged western rock lobsters (Panulirus cygnus). A Brownie tag-recapture (BTR) model was initially implemented to provide an assessment on a fishery-wide basis. Estimates from this were compared to those derived from a novel purpose-built tag-recapture individual-based model (IBM) that accounted for sex, size, month, and location-specific changes in catchability. The two models produced similar estimates on a fishery-wide scale—harvest rate (HR 0.26 vs 0.30, respectively) and legal-sized biomass (about 24,500 vs 20,735 t, respectively)—while the IBM also provided estimates on a far finer spatial and temporal scale. Both models indicate that the WCRLMF is currently in a very sustainable condition and is being fished at a rate below maximum economic yield (HRmey is about 0.39). These findings were in concert with estimates derived for this fishery based on two separate catch-rate based population models, an integrated population model and a biomass-dynamics model. Such strong agreement among all models provides great certainty in the current assessment and management of this important marine resource.

Finding lobsters: investigating a period of unusually low settlement of

Context Spiny lobsters are critically affected by ocean current movements over their long journey from hatching to swimming post-larvae (puerulus). Methods Isolating three different larval stages of the Western rock lobster (Panulirus cygnus), we have applied three-dimensional larval-dispersal modelling techniques Aims To better understand a period of unusually low puerulus settlement in the late 2000s. Key results Model results showed that transport mechanisms assisting pueruli in reaching nearshore habitats may have been inhibited by a strengthening of the southward-flowing Leeuwin Current over the austral summer at the settlement stage. As a result, modelled pueruli were transported significantly less northward, in some cases southward, during and after the period of unusually low settlement. Hatching-stage trajectories also suggest increased dispersal off the coast during 2007 and 2008, transporting modelled larvae further offshore and possibly contributing to decreased recruits into the fishery. Conclusions Our study distinguishes the influence that ocean circulation patterns off Western Australia have on three different larval stages. Implications Larval dispersal modelling of pueruli, therefore, provides a possible explanation for the changes in puerulus settlement over the past two decades and future considerations.

Changes in Panulirus cygnus Settlement Along Western Australia Using a Long Time Series

The pelagic development stages of many marine invertebrate species dictates their spatial and temporal distribution once reaching their benthic second phase of life. This life cycle is associated with the Western Rock Lobster (Panulirus cygnus) along the coast of Western Australia. Over the past 50 years, the number of puerulus reaching the nearshore reefs after their first 9 to 11 months of pelagic life in Western Australia has been monitored. These numbers, collected now at eight sites over the latitudes of the fishery, are indicative of the catchable stock 3–4 years into the future. In 2008, the fishery experienced a recruitment failure which lasted for several years before recovering to mean numbers pre-2008. This was associated with spatial and temporal shifts in the patterns of puerulus settlement. Previous research has hypothesized that physical and biological conditions in the south-east Indian Ocean no longer favored their survival. However, this decline has not been attributed to a single process. As the recovery is ongoing, contrasts in the settlement data before and after the decline are not completed. Here we characterize the data using ANOVA and pairwise comparisons to gain a better understanding of the typical patterns after the decline. Our results demonstrate that there has been a significant reduction in puerulus numbers over the first half of the season at all sites post decline. For the sites south of Lancelin there has been a significant reduction in puerulus numbers over the whole season. In addition, sites that show signs of recovery indicate that the majority of settlement occurred in the second half of the season. We anticipate these results to be the starting point for focused research into the environmental changes which may have occurred to generate these shifts in settlement numbers both from a timing and spatial perspective.

Aerobic growth index (AGI): An index to understand the impacts of ocean warming and deoxygenation on global marine fisheries resources

Ocean warming and deoxygenation are affecting the physiological performance of marine species by increasing their oxygen demand while reducing oxygen supply. Impacts on organisms (e.g., growth and reproduction) can eventually affect entire populations, altering macroecological dynamics and shifting species’ distribution ranges. To quantify the effect of warming and deoxygenation on marine organisms, Penn et al. (2018) and Deutsch et al. (2020) developed two metabolic indices that integrate physiological, biogeographic and climatic data. Here, we develop an alternative index, referred to as Aerobic Growth Index (AGI) based on an approach that integrates the von Bertalanffy growth and metabolic theory. We compare the results derived from the application of AGI with those of the two previously published metabolic indices for six species: Atlantic blue crab (Callinectes sapidus), sharpsnout seabream (Diplodus puntazzo), Atlantic cod (Gadus morhua), Australian spiny lobster (Panulirus cygnus), red drum (Sciaenops ocellatus) and common cuttlefish (Sepia officinalis). The baseline (1971–2000) habitat suitability values of AGI are significantly and positively correlated with both metabolic indices (R2 ≥ 0.92). All three indices also show similar spatial patterns and magnitudes of viable habitat loss by the end of the 21st century (2071–2100) relative to baseline conditions under a high greenhouse gas trajectory (Representative Concentration Pathway 8.5). Our results support the applicability and use of AGI to better understand the impacts of warming and deoxygenation on global marine fishery resources. Given the uncertainties surrounding mechanisms linking temperature, oxygen and biogeography, there is a need for different indicators to account for these uncertainties in climate change projections.

Size matters: large spiny lobsters reduce the catchability of small conspecifics

Indices of lobster abundance and population demography are often derived from pot catch rate data and rely upon constant catchability. However, there is evidence in clawed lobsters, and some spiny lobsters, that catchability is affected by conspecifics present in pots, and that this effect is sex- and size-dependent. For the first time, this study investigated this effect in Panulirus cygnus, an economically important spiny lobster species endemic to Western Australia. Three studies: (1) aquaria trials, (2) pot seeding experiments, and (3) field surveys, were used to investigate how the presence of large male and female conspecifics influence catchability in smaller, immature P. cygnus. Large P. cygnus generally reduced the catchability of small conspecifics; large males by 26-33% and large females by 14-27%. The effect of large females was complex and varied seasonally, dependent on the sex of the small lobster. Conspecific-related catchability should be a vital consideration when interpreting the results of pot-based surveys, especially if population demography changes. Analysis of the mean catch rate of large P. cygnus over the past 29 yr indicates that fishery management changes have created significant variations in the abundance of large lobsters. This is likely to have affected the catchability of smaller lobsters, which will have implications for the use of time series catch rate data in the stock assessment and management of this fishery.

The complete mitochondrial genome of longlegged spiny lobster Panulirus longipes (A. Milne Edwards, 1868)

In this study, we first determined and characterized the complete mitochondrial genome of longlegged spiny lobster Panulirus longipes from South China Sea. The P. longipes mitogenome is 15,739 bp long, and consists of 22 tRNA genes, two rRNA genes, 13 protein-coding genes (PCGs), and one control region. The nucleotide composition of P. longipes mitogenome is significantly biased (A, G, T, and C was 32.06%, 14.36%, 32.42%, and 21.16%, respectively) with A + T contents of 64.48%. Among 13 PCGs, COX1 gene used an unusual initiation codon CAA, COX1, COX2, ND4 and CYTB genes were ended with an incomplete stop codon T, and ND5 gene with an abnormal stop codon ATT. One microsatellite (C)10 was identified in P. longipes mitogenome located in the control region. Phylogenetic tree showed that P. longipes was first clustered with Panulirus cygnus, then together with P. japonicus and P. argus.

Gear modifications reduced humpback whale entanglements in a commercial rock lobster fishery

AbstractEntanglement of whales in fishing gear occurs globally and where populations are recovering from past exploitation, entanglement frequency is likely to increase. The Western Australian population of humpback whales (Megaptera novaeangliae) is growing rapidly, yet from 1990 to 2010 the number of whales reported entangled in gear from the pot‐based western rock lobster fishery was relatively stable at around one per year. However, from 2010, reported entanglements increased, reaching a maximum of 17 in 2013. This increase occurred immediately after a shift to a year‐round quota‐based fishery that eliminated the annual 4½‐month closure that coincided with the whale migration. Gear modifications that eliminated surface rope, shortened rope lengths, and reduced float numbers were implemented in June 2014 to reduce whale entanglements. The effectiveness of these modifications was evaluated using a Bayesian model that incorporated changes in humpback whale population size, entanglement reporting probability, fishing effort, and whale migration timing. Our analyses indicate that gear modifications reduced entanglement in fishing gear from the rock lobster fishery by at least 25% (with 95% probability), with a median reduction of 64%. The model also showed that the greatest entanglement risk occurs on the northward migration and in water depths of 55–73 m.

Automatic detection of Western rock lobster using synthetic data

Abstract Underwater imaging is being extensively used for monitoring the abundance of lobster species and their biodiversity in their local habitats. However, manual assessment of these images requires a huge amount of human effort. In this article, we propose to automate the process of lobster detection using a deep learning technique. A major obstacle in deploying such an automatic framework for the localization of lobsters in diverse environments is the lack of large annotated training datasets. Generating synthetic datasets to train these object detection models has become a popular approach. However, the current synthetic data generation frameworks rely on automatic segmentation of objects of interest, which becomes difficult when the objects have a complex shape, such as lobster. To overcome this limitation, we propose an approach to synthetically generate parts of the lobster. To handle the variability of real-world images, these parts were inserted into a set of diverse background marine images to generate a large synthetic dataset. A state-of-the-art object detector was trained using this synthetic parts dataset and tested on the challenging task of Western rock lobster detection in West Australian seas. To the best of our knowledge, this is the first automatic lobster detection technique for partially visible and occluded lobsters.

Factors Affecting the Recovery of Invertebrate Stocks From the 2011 Western Australian Extreme Marine Heatwave

The extreme Western Australia 2011 marine heatwave had a lasting effect on the marine ecosystem and after seven years, only parts of the ecosystem have showed good signs of recovery. After the heatwave, scallop fisheries in the Abrolhos Is. and Shark Bay were closed for 3-5 years, while the Shark Bay crab fishery was closed for 18 months; these fisheries at the centre of the heatwave have shown some improvement due to better protection of spawning stock and improved environmental conditions. Also at the centre of the heatwave, Roe’s abalone suffered a catastrophic mortality and has not recovered as spawning stock remains very low. The Perth abalone stock which was outside the peak heatwave area had a major stock reduction but remained opened with reduced catches. The heatwave had a marked indirect effect on brown tiger prawns in Exmouth Gulf due to loss of seagrass habitat. The heatwave also resulted in a decline in western king prawn recruitment in Exmouth Gulf, to the north of heatwave centre, but an improved recruitment in the cooler waters of Shark Bay. Western rock lobsters near the heatwave peak also appear to have been indirectly affected and have not recovered. Factors influencing the recovery rate from the heatwave appeared to be: species near their upper temperature range and/or sensitive to warming temperatures; spatial overlap between the warming event and species distribution; whether spawning stock was affected to the point of recruitment impairment; life-cycle duration of invertebrate (or habitat) species affected; and management intervention. This study provides a framework for managing the consequences of heatwaves on fisheries by highlighting the value of early identification of the event and its effect on fisheries and having flexible harvest strategies for early management intervention. This is particularly important as long-term increases in water temperatures will increase the frequency of marine heatwave events and the fisheries stocks would have less time for recovery

Optimizing an oceanographic-larval model for assessment of the puerulus settlement of the western rock lobster, Panulirus cygnus, in Western Australia

Western rock lobster larvae have a 9–11 mo pelagic larval phase that makes them susceptible to the oceanographic environment, such as the poleward-flowing Leeuwin Current, surface winds, and wave-induced Stokes drift. An innovative oceanographic-larval modelling approach, which incorporated these physical drivers and complex larval behavior, was used to investigate the cause of the major reduction in postlarval (puerulus) settlement in the late 2000s. Individual-based biophysical larval models, taking into account the sensitivity to different wind effects on the surface water movement and different levels of puerulus swimming, were developed utilizing 19 yrs of meteorological and oceanographic data (1994–2012). Model optimization was achieved by assessing modelled and observed puerulus settlements along the Western Australian coast for 24 model simulations with different combinations of model parameters. A postmodel analysis then assessed the effect of the timing of larval release, abundance and spatial distribution of larval release, and duration of larval development. Model results revealed that a mismatch between the seasonal timing of spawning, larval development, and onshore current systems needed to return the larvae to the coast appears to be the primary cause of the low settlement in the late 2000s. Since the mid-2000s, there has been an earlier start of the spawning season due to warmer winter temperatures, which may have caused the ocean currents and eddies to diffuse the larvae in the open ocean before they can be transported back to the coast by onshore currents and weakened winter storms.

Methodological comparison for sampling populations of a commercially important rock lobster species

Wild populations of rock lobsters are sampled to aid in assessments of the fisheries stocks, the impact of marine reserves, as well as biological and ecological studies. The two most prevalent methods for sampling rock lobsters are pots (traps) and diver-based surveys. While many studies have individually investigated the inherent biases and uncertainties for these methods, no thorough comparison across these methods has been completed. Here, we examined four pot designs and two diver surveys methods for their ability to adequately sample the western rock lobster, Panulirus cygnus George, 1962. Methods were tested for their ability to: (1) capture sufficient individuals, (2) sample a large size-range, and (3) detect differences in relative abundance. A modified pot design, meshed recreational, proved to be the most efficient and unbiased of all the methods examined. These pots sampled an average of 177 lobsters d–1, captured a large range of lobster sizes (40.4–158 mm), and were capable of detecting known patterns in abundance. Abundance indices produced by the two dive-based methods were found to be less accurate in detecting the patterns of known abundance, and did not produce better size-composition data than the modified pots. It is likely that variation in habitat complexity meant the two dive methods were inefficient for sampling P. cygnus in the present study. Outcomes presented here highlight the need to carefully select methods appropriate to the particular species, its habitat, and the aims of the study being conducted.

Changes in fishing effort efficiency under effort and quota management systems applied to the Western Australian rock lobster fishery

Fishing efficiency changes in the western rock lobster fishery, Panulirus cygnus George, 1962, have been assessed to improve the reliability of the commercial catch rate–based breeding stock indices and effective effort that contribute to a length-based stock assessment model. The present study covers the fishery under transferable effort quotas from the 1980s to 2009, and under catch quota management from 2010. To evaluate the changes in effective effort and lobster abundance through these events, fishing efficiency has been determined using standardized abundance indices from six independent survey locations in offshore breeding stock areas. Catch rates from these independent surveys (instituted 1994) have been compared with industry catch rates on adjacent grounds to estimate effort efficiency increases in the breeding stock areas. The catch rate calibration revealed that the deep water breeding stock areas had efficiency increases of 2.7%–3.6% per annum under effort control, while the shallower water breeding stocks in the offshore Abrolhos Islands were less affected. The change to catch quota management resulted in a marked decrease in effort efficiency of around 30%; however, the short time series since this management change does not provide a reliable trend of efficiency changes. Factors influencing fishing efficiency, including the management system itself, are considered and the need for validation of catch-rate based management performance indicators is discussed. Our study highlights the benefits of using fishery-independent surveys to evaluate effort efficiency changes and in addressing the biases normally associated with abundance measures based on commercial catch rates.