Western Rock Lobster Fishery Research Articles

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.

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.

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.

Climate variability affecting the contranatant migration of Panulirus cygnus, the western rock lobster

Large-scale animal migrations have high energetic costs and are only undertaken for specific biological outcomes, including opening up habitat resources or for reproduction. Juvenile western rock lobsters (Panulirus cygnus) migrate firstly offshore and then northwards from their inshore nursery areas (<40 m) into breeding grounds (40–100 m). In the 2000s, catches of migrating lobsters in the northern part of the western rock lobster fishery declined and concerns were raised as to the sustainability of this stock. This study has documented the substantial inter-annual variation in the latitudinal distribution (between latitudes 27° and 30° S) of migrating lobsters in deep water. This distribution was found to be highly correlated with the sea-floor meridional current strength in January and mean latitude and abundance of puerulus (post-larvae) settlement 3–4 years previously. Combined, these indices explained 92 % of the annual variation in the latitude of migration, and the majority of the variation in commercial catches towards the north of the fishery. These indices are all either directly or indirectly impacted by the south-flowing Leeuwin Current. This current, which is influenced by ENSO conditions, has increased in strength over the last 20 years, a trend that has been identified as a relatively short-term decadal shift, while climate change models project a progressive reduction in the strength of this current in the longer term. This may result in greater northward lobster migrations and a shift in the biomass of lobsters more towards the northern end of the fishery.

Maximum economic yield of the western rock lobster fishery of Western Australia after moving from effort to quota control

The western rock lobster (Panulirus cygnus) fishery is Australia’s most valuable single-species fishery, worth AUD$200–$400 million annually. Stock assessment for this fishery utilises the puerulus settlement to predict recruitment to the fishery 3–4 years later. This predictive ability has been particularly useful recently, due to an unprecedented period of low settlement between 2006/07 and 2012/13. Pre-emptive management action (~70% effort reduction) was taken to provide greater protection to the breeding stock which also moved the fishery to the maximum economic yield (MEY) level of effort for the projected recruitment. In 2010/11, the fishery moved from an effort-controlled to a quota-controlled fishery, which led to changes in fishing practices resulting in reductions in fishing costs and increases in lobster prices of about US$16/kg. This provided a unique opportunity to compare an MEY assessment under effort and quota controls. The MEY assessment under quota controls for a 5-year period indicated that annual harvest rates of 37–47% of legal biomass will achieve catches of 5780–7370t. in 2014. This MEY target harvest range, which complements existing sustainability reference points based on egg production, is robust to a range of costs, prices and profit discount rates. This catch range enables industry/managers to take into account marketing implications and social issues (e.g. employment) in quota setting and therefore could be considered a socio-economic target. The MEY level of fishing has increased egg production to well above threshold levels that were based on maximum sustainable yield, providing the fishery with increased resilience when faced with environmental perturbations. This enables consideration for relaxing some existing biological controls, e.g. setose (mature) females, females above a maximum size, and lobsters 76–77mm carapace length. The relaxation of these controls is estimated to increase profits by about AUD$15 million annually due to higher catch rates and reduced fishing effort while maintaining egg production well above threshold levels.

What caused seven consecutive years of low puerulus settlement in the western rock lobster fishery of Western Australia?

AbstractPuerulus settlement in the western rock lobster fishery has remained below average for seven consecutive years (2006/2007–2012/2013), with 2008/2009 being the lowest in over 40 years. Examination of the timing of the start of spawning using fishery-independent data since the mid-2000s indicated that spawning has been occurring earlier. The low settlement appears related to higher water temperatures at the time of the onset of spawning (October) since the mid-2000s. Statistical analysis shows that the most (71%) of the variation in puerulus settlement was explained by the timing of spawning, storm activity during autumn/spring, and offshore water temperatures in February. Earlier spawning may cause a mismatch with other environmental factors such as peaks in ocean productivity and/or storms that assist the larvae return to the coast and offshore water temperatures that help the early stage larval growth. These variables produced a plausible hypothesis to explain the decline in puerulus settlement for these 7 years, including the recruitment failure of 2008/2009. They also predicted the substantial improvement in settlement for 2013/2014. Egg production levels did not to have a significant relationship with puerulus settlement levels after taking environmental variables into account. Further verification with additional years is required to see whether this relationship is maintained. Global climate change may influence these environmental factors: the timing of spawning is influenced by water temperature and there has been a reduced trend of autumn to spring storms off southwest Australia.

The orientation and migratory dynamics of the western rock lobster, Panulirus cygnus, in Western Australia

AbstractLarge-scale migrations are known to occur in numerous species, and in the case of the Western Rock Lobster, Panulirus cygnus, result in juveniles moving from nursery areas into deeper offshore breeding grounds. In 2008 the Western Rock Lobster fishery reduced harvest rates to increase legal and spawning biomass throughout the fishery, which also allowed greater numbers of lobsters to migrate. Increased lobster migration could potentially reduce biomass in some areas, thus adversely impacting commercial catch rates. Over 20 000 tag–recaptured lobsters were analysed to determine the dynamics underlying migration in this species and to assess the impact reduced harvest rates may have had on catches. This study showed that P. cygnus migration was associated with body size and water depth, and that magnetism and oceanic currents appear to be the most likely guideposts used for orientation. Size at migration varied in a constant fashion along the coast, being larger towards the southern end of the fishery and smallest at the offshore Abrolhos Islands. During the migration period, up to 50% of lobsters at their mean size of migration moved from coastal areas out towards deeper waters (&gt;40 m), whereas &lt;15% of those in deeper water at the same size moved significant distances northward. This behaviour appears to be contranatant, counteracting the downstream redistribution of larvae after their 9–11 month larval life. Reduced harvest rates and catches being focussed onto higher valued sedentary lobsters have allowed more lobsters to migrate. However, the numbers moving between management areas are relatively small, with the biological and economic benefits of fishing at a reduced exploitation rate outweighing losses to catches.

Evaluating the ecosystem effects of variation in recruitment and fishing effort in the western rock lobster fishery

We used a regional, ecosystem mass-balance model (Ecopath with Ecosim) to evaluate the possible changes in flows of mass and energy between the benthic and pelagic components of the marine ecosystem of Jurien Bay in temperate Western Australia (∼30°S, ∼115°E). The effects of varying the biomass of western rock lobster in the system were examined by simulating changes in commercial and recreational fishing mortality as well as recruitment-driven changes in the abundance of lobster puerulus (the first post-larval stage). The model comprised 80 functional groups (more than 200 species). A simulated closure of the commercial lobster fishing was predicted to lead to an increase in lobster biomass of 160% after 20 years, with changes in biomass of up to 20% of the main prey and predators of lobster. Since 2006/2007, the puerulus settlement (recruitment to the benthos) of western rock lobster has declined to the lowest levels recorded in the fishery. The model predicted that under 2005 levels of fishing effort, a simulated depletion of 90% of puerulus biomass resulted in an ∼17% reduction in the biomass of adult lobster biomass after 20 years (i.e. by 2025). In general, the model predicts that the variations in lobster biomass, whether induced from fishing mortality or declining puerulus settlement, have relatively small effects on the biomass of the main predators and prey of lobster in the marine park. The relative biomass of adult rock lobster and their associated predators and prey was more sensitive to fishing than to variations in recruitment.

Assessing the effects of moving to maximum economic yield effort level in the western rock lobster fishery of Western Australia

Abstract The western rock lobster ( Panulirus cygnus ) fishery has been facing significant economic pressure from increasing costs, lower prices as well as predicted reduced catches due to low recruitment. A maximum economic yield (MEY) assessment estimated the fishing effort that would maximise the net present value of profits over 2008/09–2013/14 was about 50%–70% reduction of 2007/08 effort. The assessment accounted for fixed vessel costs and the variable pot lift cost. An important component of this assessment was the use of puerulus settlement time series that provided a reliable predictor of recruitment to the fishery 3–4 years later. This can be contrasted to most MEY assessments that would use an average catch-effort relationship rather than taking into account the expected recruitment. This predictive ability has been particularly useful as there has been a period of unusually low puerulus settlements over the 5 years (2006/07–2010/11) including the lowest two settlements in the 40-year time series. Due to the low settlements, substantial management changes were implemented in 2008/09 and 2009/10 (44% and 73% reduction in nominal fishing effort, respectively compared to 2007/08) to maintain the breeding stock at sustainable levels by having a significant carryover of legal lobsters into future years of lower recruitment. These effort reductions provided a unique opportunity to assess the economic impact of a fishery moving to an MEY effort level over two years. The CPUE increased from 1.1 kg/pot lift in 2007/08 to 1.7 and 2.7 in 2008/09 and 2009/10, respectively. These CPUEs were much higher than the expected levels (1.2 and 1.1, respectively) if the 2007/08 effort had been maintained in these two years. The vessel numbers declined by 14% and 36% in 2008/09 and 2009/10, respectively, compared to 2007/08. The fishery profit increased by AUS$13 and 49 million for 2008/09 and 2009/10, respectively, compared to that estimated if the 2007/08 effort level had continued. This assessment demonstrates the economic benefits of fishing at a level close to that estimated for MEY under an input management regime. The management decision-rule framework is currently based on having the egg production above a threshold reference level to ensure sustainability and now a target reference point based on MEY principles is also being considered.

Depletion‐based population estimates for western rock lobster (Panulirus cygnus) fishery in Western Australia

A depletion technique was applied to the western rock lobster fishery in Western Australia for the non‐migrating part of the season, March to June. The catch for the migrating part of the fishery was used to estimate the annual exploitation for the whole season. To take into account environmental effects (water temperature and swell) on catchability that affect the assumptions of the depletion technique, estimates of the changes in catchability between March and June of each year were obtained. The trends in catchability, residual biomass and exploitation for three zones of the fishery since the 1983/84 season were examined. These show that the exploitation in the north coastal zone decreased from c. 75% in the early 1990s to c. 60% in the mid 1990s as a result of a major change in management in 1993/94 (including 18% nominal effort reduction and increased protection of mature females). However, in the last 10 years exploitation has increased again to c. 75%, mainly owing to increases in catchability (e.g., efficiency increases) as there has been little change in the nominal effort. The results from this study provide some insight into changes in catchability that can be used in other stock assessment techniques such as length‐based assessments.

Impact of lunar cycle and swell on the daily catch rate of western rock lobster (Panulirus cygnus) using time series modelling

The western rock lobster fishery is one of the most valuable single‐species fisheries in Australia, valued at AU$300 million per year. The impact of environmental factors such as lunar cycle and swell on the daily catch rate of the western rock lobster (Panulirus cynus) is of particular interest in the stock assessment and management of the fishery. The variation in daily catch rates was examined for two periods (migrating period November‐January, non‐migrating period February‐June), at different depths in three management zones for three categories of lobster (undersize, legal size, and setose). Regression and transfer function models for relationships between catch rates and environmental data were considered and compared. The lunar cycle has a significant impact on the daily catch rates with c. 30% lower catch rate during the full moon and c. 20% higher catches near the new moon. This impact occurs mainly during the non‐migrating period both in deep water (40–100 m) and shallow water (<40 m). The swell on the day before fishing was also shown to be significantly related to the catch rate with an increase of c. 10–15% for an increase in swell from light to moderate or moderate to high. These environmental factors can be used to standardise catch rates to provide an improved abundance index for stock assessment. Also, management closures are being considered for 3–5 days over the low catch rate, full moon period to reduce fishing costs and lower fishing effort.

Regional Prediction of the Western Rock Lobster, Panulirus Cygnus, Commercial Catch in Western Australia

The puerulus settlement at 2 sites on the Western Australian coast has proved to be a reliable predictor of total catch of the western rock lobster fishery, up to 4 years ahead. Over the last 10 years the puerulus settlement has been monitored over a wider area of the fishery enabling regional variation in puerulus settlement to be assessed and allowing regional prediction of catches. Analysis of the three main regions of the fishery (Abrolhos Is., North and South Coastal) indicate that settlement within these regions provides a more accurate predictor of regional catches. This was illustrated in 1991/92, when a higher than expected catch was obtained in the Southern region due to record puerulus settlement at the southern sites in 1988/89. Only average settlement was obtained at the more northern sites, Dongara and Jurien, for 1988/89 and so an average catch was predicted for 1991 /92. The regional analyses have also highlighted the significant effect that the increase in fishing effort in the North Coastal region has had in explaining the variation in the catch, after taking into account the effect of the puerulus settlement. The variation between regions in density-dependent effects between puerulus and recruitment to the fishery is examined.

Increases in fishing effort in a limited entry fishery - the western rock lobster fishery 1963-1976

Increases in fishing effort in a limited entry fishery - the western rock lobster fishery 1963-1976

Population dynamics and management of the western rock lobster fishery

Population dynamics and management of the western rock lobster fishery