Management strategy evaluation for rock lobster,Jasus edwardsii,off Victoria,Australia: Accounting for uncertainty in stock structure

The management strategy evaluation (MSE) approach was used to evaluate management strategies based on the current method of stock assessment for rock lobster (Jasus edwardsii) off Victoria, Australia, and decision rules inferred from the management plan for Victorian rock lobster and past practice when selecting total allowable catches, TACs. The results are expressed in terms of whether it is possible to keep stocks above limit reference points with high probability and recover over‐exploited stocks to the target level. Three categories of management strategy were examined using the MSE, which differed in whether assessments were conducted, and TACs set, by management zone or by region within management zone. A management strategy based on conducting assessments and setting TACs by management zone is most similar to the way assessments are currently conducted and management regulations implemented for rock lobster off Victoria. However, this management strategy performed poorest in recovering stocks to target levels. Alternative management strategies which involved conducting assessments and setting TACs by region performed better, but may have practical limitations. The assessment method was found to be generally relatively accurate and precise, although estimation performance was poor/imprecise on occasion.     

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.     

Effect of reproductive state and sex on movement and food consumption of western rock lobster (Panulirus cygnus) in a tank environment

The catchability of western rock lobsters (Panulirus cygnus) during the spawning season (October and November) may be affected by their reproductive state. In this study, movement and food consumption of males and females of different reproductive states held in laboratory tanks were measured as proxies for catchability. Density of lobsters was found to influence both movement and food consumption. Solitary animals and, to a lesser extent, two lobsters per tank, were more sedentary and consumed significantly less food than animals at a density of three or four specimens per tank. Tests using three animals per tank confirmed that mature, unmated, and ovigerous females carrying early stage eggs moved more frequently away from their shelters than males or females carrying late stage eggs (P < 0.0001, d.f. = 3). Further, unmated females and females with early stage eggs recorded significantly higher food consumption (P < 0.0061, d.f. = 3) compared with males or females carrying late stage eggs. The greater time spent away from shelter and also food consumption make unmated females and females with early stage eggs likely to be more catchable than males or females with late stage eggs. As catchability is commonly used to obtain population estimates from survey data, these results have implications for surveys which use catch rates of breeding animals as indicators of egg production.     

Predicting survival of western rock lobsters Panulirus cygnus using discriminant analysis of haemolymph parameters taken immediately following simulated handling treatments

Instances of morbidity amongst rock lobsters (Panulirus cygnus) arriving at factories in Western Australia (WA) have been attributed to stress during post‐harvest handling. This study used discriminant analysis to determine whether physiological correlates of stress following a period of simulated post‐harvest handling had any validity as predictors of future rejection or morbidity of western rock lobsters. Groups of 230 western rock lobsters were stored for 6 h in five environments (submerged/flowing sea water, submerged/recirculating sea water, humid air, flowing seawater spray, and recirculated seawater spray). The experiment was conducted in late spring (ambient sea water 22°C), and repeated again in early autumn (ambient sea water 26°C). After 6 h treatment, each lobster was graded for acceptability for live export, numbered, and its haemolymph was sampled. The samples were analysed for a number of physiological and health status parameters. The lobsters were then stored for a week in tanks in the live lobster factory to record mortality. The mortality of lobsters in the factory was associated with earlier deviations in haemolymph parameters as they emerged from the storage treatments. Discriminant analysis (DA) of the haemolymph assays enabled the fate of 80–90% of the lobsters to be correctly categorised within each experiment. However, functions derived from one experiment were less accurate at predicting mortality when applied to the other experiments. One of the reasons for this was the higher mortality and the more severe patho‐physiological changes observed in lobsters stored in humid air or sprays at the higher temperature. The analysis identified lactate accumulation during emersion and associated physiological and haemocyte‐related effects as a major correlate of mortality. Reducing these deviations, for example by submerged transport, is expected to ensure high levels of survival. None of the indicators tested predicted mortality with total accuracy. The simplest and most accurate means of comparing emersed treatments was to count the mortality afterwards.     

Modelling the effects of Marine Protected Areas (MPAs) on the southern rock lobster (Jasus edwardsii) fishery of Victoria,Australia

Since 2002, 5.3% of the Victorian coastal waters have been declared as Marine Protected Areas (MPAs). These are aimed at safeguarding important marine habitats and species, significant natural features, and areas of cultural heritage and aesthetic value. However, MPAs impact the fishery for southern rock lobster (Jasus edwardsii), as total allowable catches (TACs) were previously set to allow the biomass to recover to pre‐specified target levels. The model on which assessments and risk analyses are based is extended to include the impact of MPAs. The MPAs and the area open to fishing are modelled as subpopulations with different levels of mortality and consequently different density and population size‐structure. A range for the probability of a lobster moving from a MPA to the fished area from 0 to 15% is considered, based on the results of tagging studies. The reduction of biomass available to the commercial fishery because of the introduction of MPAs is estimated to be 8% and 16% (Western and Eastern Zones) respectively. The results of a risk assessment show that if the current TACs are maintained, the time to increase the biomass available to the commercial fishery by 50% would be delayed 5–9 years in the Western Zone and 1–4 years in the Eastern Zone because of the impact of displaced effort. In contrast, spawning biomass in the Eastern Zone is currently below the agreed limit reference point, and the introduction of MPAs would enhance the rate of recovery, although only marginally initially, faster than the absence of the MPAs.     

Comparison of catches on two types of collector of recently settled stages of the spiny lobster (Panulirus argus), Florida,United States

This study compared catches of Panulirus argus pueruli and very young juveniles between Hunt and Sandwich collectors at Long and Big Munson Keys, Florida, United States. Catch comparisons were made over the peak puerulus settlement period between February and July 2002, using six Sandwich and six Hunt collectors at each site. The collectors were set out in arrays and the relative positions of the two collector types were reversed each month after they had been checked and the catch removed. A total of 3470 pueruli and juveniles were collected; 2011 and 1459 by Sandwich and Hunt collectors, respectively. Sandwich collectors caught an average of 5.43 more pueruli and juveniles per check than Hunt collectors, with this difference being significant for catches of clear pueruli (P1s), pigmented pueruli (P3s), and juvenile stages (J1s and J2s) (P < 0.05), but not for catches of semi‐pigmented pueruli (P2s). The catches made by both collector types were highly dependant on the month of collection and site of the collectors (P < 0.01). Catches were generally not influenced by the location of the collector in the array (P = 0.50), but corner collectors caught significantly fewer P1s, P2s, P3s, and J1s and J2s than all other collectors (P < 0.01). Conditioning time influenced the total catch (P < 0.01) but was not significant for all individual P1s, P2s, P3s, and J1s and J2s stages of development. Overall, the time taken for collectors to condition in Florida was less than the Sandwich collectors used for P. cygnus in Western Australia.     

Characterisation of the recreational fishery for southern rock lobster,Jasus edwardsii,in Tasmania,Australia: Implications for management

Southern rock lobster (Jasus edwardsii) support significant commercial and recreational fisheries in Tasmania, Australia. Since the mid 1990s the number of persons holding recreational lobster licences increased by over 80%, with c. 15 500 persons licensed in 2002/03. Assessment of the recreational fishery has been undertaken periodically since 1996 using a telephone‐diary survey method. The fishery was concentrated off the south‐east and east coasts of Tasmania and characterised by strong seasonality in catch and effort, which peaked markedly early in the fishing year (November‐January). Although pots were the most popular fishing method, daily catch rates by divers were more than double those for pots. Divers selectively harvested larger lobsters than those taken by pots and more frequently attained the daily bag limit of 5 lobsters. The estimated recreational harvest increased significantly since 1996/97 and in 2002/03 effectively reached a management trigger level of 10% of the total allowable commercial catch, flagging a review of recreational management arrangements.     

Direct impacts of commercial and recreational fishing on spiny lobster,Panulirus interruptus,populations at Santa Catalina Island,California, United States

The California spiny or red rock lobster, Panulirus interruptus, is an ecologically and economically important species that has been exploited since the 1800s. No previous study in California has assessed the impacts of the recreational or commercial lobster harvest. Before the 2003–04 commercial and recreational lobster seasons, we conducted a fishery‐independent trap survey at Santa Catalina Island to document the impact of the lobster fisheries on the size structure, abundance, and sex ratios of mature P. interruptus (>65 mm carapace length (CL)). We concurrently sampled a predominantly commercially fished area, a recreationally fished area, and a 23‐year‐old invertebrate no‐take (INT) reserve. Relative to the INT reserve, legal‐size lobsters in the recreational area were similar in CL, but 31% less abundant. Legal‐size lobsters in the commercial area were 8% smaller and 70% less abundant than those in the INT reserve. The sex ratio of legal‐size lobsters, although near 50:50 in the recreational and INT reserve areas, was male‐dominated (67:33) in the commercial area. Differences in CPUE and mean CL of sub‐legal lobsters in the recreational and commercial areas suggest that factors in addition to harvesting pressure may affect these populations. Total biomass of mature lobsters in the recreational and commercial areas was 92% and 45%, respectively, of biomass in the INT reserve. Fecundity in the recreational and commercial areas was 83% and 42%, respectively, of fecundity in the INT reserve. This study provides preliminary data for future ecological studies and fisheries management evaluations.     

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

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.     

Measuring depth of settlement in the red rock lobster,Jasus edwardsii

Settlement of the puerulus stage of Jasus edwardsii (Decapoda: Palinuridae) near the shore takes place over a wide depth range. It occurs intertidally, and, as determined by crevice collectors, also takes place down to depths of at least 50 m. At sites along the east coast of the North Island of New Zealand, depth of greatest settlement found on collectors varied with locality and time, but was within the upper 11.5 m. Surface‐buoyed collectors caught fewer animals than did collectors at greater depths. Settlement levels generally increased with depth to about 10–12 m, then decreased with increasing depth and distance from shore. The ability of/, edwardsii to settle over a wide depth range may improve its chances of recruitment. A device (closing crevice collector) for measuring puerulus settlement of J. edwardsii at depth is described.     

Settlement patterns,size and growth of puerulus and juvenile rock lobster Jasus lalandii at an oyster farm in Saldanha Bay,South Africa

Trends in the abundance, size and growth of newly settled pueruli and early juveniles of the rock lobster Jasus lalandii were determined from samples obtained from mesh bags used for oyster mariculture in Saldanha Bay, South Africa. Totals of 3 842 lobster pueruli and 10 158 juveniles were captured between August 2005 and June 2006, and distinct puerulus settlement events were identified in November and January. Juveniles also peaked during these months as well as in March. The size of newly settled pueruli increased significantly between October and March. The carapace length (CL) of pueruli and juveniles overlapped between 8.5 mm (smallest juvenile) and 10.4 mm (largest puerulus), and 50% of pueruli moulted into juveniles by 9.5–9.6 mm CL. There was a size progression in juveniles, with larger individuals in February and March reflecting an accumulation of juveniles from the earlier settlement events. The estimated growth increment from puerulus to first juvenile instar was 0.5–1.5 mm (4.9–16.1%), increasing to 1.4–2.5 mm (14.4–23.3%) for the second instar. Recruitment of J. lalandii pueruli occurred during periods when strong southerly winds prevailed, which results in a general offshore movement of surface waters along the West Coast and upwelling of cold nutrient-rich bottom waters. However, specific settlement events appeared to coincide with a change in wind direction, reduction in upwelling strength and increase in surface water temperatures, implying that larvae may take advantage of landward movements of surface waters during downwelling, or reversal of upwelling, to return them to shallow coastal waters.     

Impacts of unconstrained effort: Lessons from a rock lobster (Jasus edwardsii) fishery decline in the northern zone management region of South Australia

The Northern Zone rock lobster fishery of South Australia is expansive, covering an area of ∼207,000 km². From 1970 to 2002 it was managed under input controls that relied heavily on restrictions to days-at-sea and size limits. In 2003, output controls in the form of individual transferable quotas with a total allowable commercial catch were also introduced. Fishery performance from 1980 to 2007 was analysed based on catch data and model outputs. Trends in catch and effort increased through the 1980s and 1990s while nominal catch rate remained relatively stable. However, from 1999 to 2003 catch decreased by 49% from 1001 to 503 ton and has remained at <500 ton since. Importantly, nominal effort did not decline comparatively, decreasing by only 12% from 1999 to 2007. Consequently, nominal catch rate decreased by 47.5% from 1.43 to 0.75 kg/potlift, over the same period. Logbook data revealed strong evidence of spatial expansion through the 1980s and 1990s which is likely to have masked declining lobster abundance and contributed to a “hyperstability” scenario in catch rates. It is suggested that increasing effective effort, driven by advances in fishing technology and vessel design, fuelled this expansion. Model outputs, which account for increases in effective effort, indicate that biomass has decreased by ∼68% since the 1980s. The results highlight the limitations associated with input controls in controlling effort during periods of spatial expansion. Further evidence from puerulus settlement data stresses the importance of conservative quotas for lobster fisheries where annual recruitment is low or highly sporadic.     

High levels of site fidelity in movement patterns of Southern Rock Lobster (Jasus edwardsii) in Victoria,Australia

ABSTRACT

Movement patterns of the Southern Rock Lobster Jasus edwardsii in Victoria, Australia were investigated from 8,533 tag-recapture events across a 20-year period (1992–2012). In total, 83% of lobsters were recaptured within 1?km of their tagging site and 93% within 5?km. While largely resident, elevated movements were observed within specific regions, with the overall direction of movement being from inshore to offshore areas. Movement was not impacted by lobster sex, size, or reproductive stage. The fishery for Southern Rock Lobster within Victoria is currently managed into two zones with separate total allowable commercial catches in each area. Given the high levels of site fidelity, our findings suggest that management of the resource at this spatial scale is appropriate and that consideration of significant movement between zones is not warranted in fishery stock assessment models.     

Spatial and temporal patterns in the distribution and abundance of macrozooplankton on the southern North West Shelf, Western Australia

We describe the spatial and temporal dynamics of macrozooplankton on the southern North West Shelf (NWS) of Australia over two consecutive summers (1997/1998 and 1998/1999). Sampling was conducted using submersible light traps, deployed at the surface and at depth, along one cross-shelf transect in 1997/1998, and along two cross-shelf transects and one long-shore transect in 1998/1999. Our results revealed large inter-annual changes in macrozooplankton assemblages during the two summers. An upwelling regime associated with El Niño conditions prevailed during the first summer, resulting in high chlorophyll concentrations and an abundance of both meso- and macrozooplankton. During this time, there were distinct inshore and offshore macrozooplankton assemblages that reflected an abrupt transition from upwelling-enriched shelf waters to oligotrophic oceanic waters. In contrast, the second summer was characterised by a downwelling regime associated with La Niña conditions that resulted in low chlorophyll concentrations and decreased abundances of meso- and macrozooplankton. The lack of upwelling activity weakened horizontal gradients in macrozooplankton assemblages so that differences between surface and deep assemblages were more pronounced. Catches in light traps were dominated by hyperiid amphipods during the first summer and by the neritic euphausiid Pseudeuphausia latifrons during the second. There was little within-season change in macrozooplankton assemblages during both summers, and only weak relationships were found between the environmental parameters and the distribution of individual macrozooplankton taxa.