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.

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

Dynamics of ocean boundary currents and associated shelf processes can influence onshore/offshore transport of water, 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, transport them back to the coast. The abundance of western rock lobster puerulus (settlement phase post phyllosoma) has historically been observed to be positively correlated with the strength of the Leeuwin Current, and an index of puerulus numbers is used by fisheries managers as a predictor of subsequent lobster abundance 3–4 years later. 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 important for fisheries management. Oceanographic parameters likely to influence puerulus settlement were derived for a 17 year period to investigate correlations. Analysis indicated that puerulus settlement at adjacent monitoring sites have 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 south-east 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, that 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.

Investigating ecosystem processes using targeted fisheries closures: can small-bodied invertivore fish be used as indicators for the effects of western rock lobster fishing?

Ecosystem modelling has predicted that fishing for western rock lobster Panulirus cygnus in deep water (50–80m) habitats will result in increased abundance of their macroinvertebrate prey, which would, in turn, support greater production of small-bodied invertivore fish species. To investigate the potential ecosystem effects of rock lobster fishing, a targeted fisheries closure was proposed in deep water habitats along the coast of Western Australia. Data on small-bodied invertivore fish abundance, from baited video, were used to investigate differences across habitats and simulate the likely power of any study to detect change. In general, small-bodied invertivore fish were more abundant at shallower macroalgae-dominated sites, whereas the most abundant single species, the western king wrasse Coris auricularis, was abundant across all habitats and sites. Power simulation of a mixed-model before–after–control–impact (BACI) design found that a 40–50% decrease in either Coris auricularis or small-bodied invertivore fish in general would be very likely to be detected (power ~0.8). Based on the power simulation, we suggest a general sampling design to investigate change before and after the establishment of the fishery closure and make suggestions for further ecological studies to investigate the predicted ecosystem effects of rock lobster fishing.

A review of lobster fishery management: the Western Australian fishery for Panulirus cygnus, a case study in the development and implementation of input and output-based management systems

Lobster stocks around the world support high-value fisheries with production currently about 260,000 tonnes annually. The largest fisheries harvest Homarus, Nephrops and Panulirus species with smaller production from the Jasus, Palinurus and Scylarid species groups. The majority of larger industrial fisheries have systems limiting fishing effort or catches, while many of the smaller fisheries remain open access and have yet to implement basic management controls. The review uses the Western Australian fishery for Panulirus cygnus, valued between AUS$200–400 million annually with a long history of successful management, as a case study for the consideration of lobster fisheries management systems more generally. The conclusions from the review suggest that an evolutionary approach to management with biological controls as a precursor to input-based controls is necessary to allow sufficient fishery-based data to be accumulated for management decision processes to be effective. The case study experience suggests that well-defined fishing rights leading to an input-based total allowable effort system with individually transferable effort (ITE) units can provide efficient mechanisms for the reduction of latent effort, which characterises most lobster fisheries with open access or basic limited entry. Further the system has been shown to be capable of generating significant license values for fishermen while maintaining owner-operators as the dominant group in the fishery. The ITE system was also used effectively to adjust fishing to compensate for a severe environmentally-driven downturn in recruitment, but resulted in highly complex management rules. In 2010 the fishery moved seamlessly to a total allowable catch with individually transferable quotas which removed the complexity of management, further increased the catch value and reduced costs of fishing. Price/earnings (P/E) ratios have been used to track trends in license values which highlight the industry’s increasing economic viability over time under both input and output based management.

Condition of larvae of western rock lobster (Panulirus cygnus) in cyclonic and anticyclonic eddies of the Leeuwin Current off Western Australia

Changes in the offshore oceanographic processes are suspected to be the cause of a recent dramatic decline in the settlement of post-larvae of the Western Australian spiny lobster (Panulirus cygnus), which has greatly reduced the productivity from the world’s second-largest spiny lobster fishery. The present study assessed whether there are differences in the nutritional condition of the larvae of P. cygnus sampled from two pairs of cyclonic eddies (CEs) and anticyclonic eddies (AEs). Morphometric and biochemical analyses were undertaken on the mid–late-stage larvae (VI, VII, VIII) sampled offshore from two pairs of adjacent counter-rotating mesoscale eddies in the Leeuwin Current off Western Australia. The results showed that larvae captured from CEs had greater average total dry mass (P<0.001) than those from AEs. Stage VIII larvae from CEs contained more protein (P<0.008) (38.5% ±5.4s.e.) and lipid (P<0.005) (67.2% ±12.1) than did those from AEs. The possible causes for these differences are uncertain but may be related to differences in water temperatures in CEs v. AEs influencing the ability of phyllosomas to accumulate nutritional reserves.