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

Assessing possible environmental causes behind the reduced colonisation of western rock lobster puerulus collectors by a wide suite of species. FRDC report : project 2008/085

Objectives 1) Begin monitoring the community composition of marine flora and fauna along the Western Australian coastline during this current poor settlement period. 2) Develop standard methodology for monitoring the spatial and temporal variability in the settlement of marine flora and fauna. 3) Determine what environmental parameters may be linked to the majority of variation in the floral and faunal communities colonizing puerulus collectors, focusing on those relating to puerulus settlement. 4) Identify indicator marine flora and fauna species for monitoring the influences of environmental change on Western Australian marine environment. 5) Detect any known or potential introduced marine pests within the Western Australian environment

Higher water temperature leads to precocious maturation of western rock lobsters (Panulirus cygnus), but are things that simple?

During a rock lobster post-puerulus grow out project, western rock lobsters from three different cohorts (post-puerulus, year-1 and year-2) were held for 12 months under two temperature regimes (ambient and 23oC) and two feed delivery treatments (the same ration of pelleted diet fed once nightly and in the alternate treatment, thrice nightly). At the end of the trial, 43% of females from the largest cohort (2-year post settlement) in the 23oC treatment, had ovigerous setae. However, none of the animals held at ambient temperatures showed signs of maturity. Feed delivery did not influence the presence or absence of ovigerous setae. Male maturity responded to elevated temperature in the same way as for females, as indicated by merus/carapace length ratios. The response of female size at maturity to 23oC was compared to a similar trial in the 1970s in which 2-year post settlement animals wereheld at 25oC. Maturity of females in that study was one year later than in the trial reported here, indicating that there may have been a decrease in age at maturity since the 1970s. The conclusion from this and research on other rock lobster species, is that size/age at maturity is likely to be a complex response to a range of contributing factors of which temperature is an important one

Development of an industry-based habitat mapping/monitoring system FRDC Project No 2011/021

Mapping / monitoring in the marine environment can be a very costly exercise. Scientists from the Department of Primary Industries and Regional Development; Fisheries Division (FD) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) have developed a small, low-cost automated camera system that, when fitted to commercial fishing gear, can achieve this at minimal cost. The POTBot (Pictures Of The Bottom) system is a cheap, small “smart” camera that can track its position globally and the date and time, and can record high-definition video and water temperature readings when it determines it has been deployed into the ocean

Pilot phase trial to quantify the extent and relevance of any deepwater puerulus settlement that may have taken place in the Western Rocklobster Fishery

This study had two objectives. Firstly to trial modifications to commercial western rock lobster pots, so as to sample as wide a size range of lobsters on the grounds as possible. Sampling took place over a 10 day period between 13-24 September 2009, with seven commercial fishermen being responsible for collection of the data at different sampling locations (Mandurah, Fremantle, Lancelin, Dongara, Geraldton, Abrolhos and Kalbarri). This arrangement proved to be successful in that a wide area of the coast was covered by the sampling regime and good quality catch composition data was achieved across the four depth zones (0-10 fm, 10-20 fm, 20-30 fm and >30 fm) that were sampled. The different pot modifications that were trialled sampled a wide size range (25-144 mm CL), but mostly caught lobsters around the legal size limit (modal size, 80 mm CL). In three of the four areas where more than one pot type was used, there were significant differences (p<0.01) in the catch rates of one or more size classes between the various pot types.The second objective was to establish whether there has been a shift in post-puerulus settlement from shallow to deeper waters. Analysis showed that depth was highly significant (p<0.05) in determining the catch rates of most size classes (≤50 mm CL; 51-65 mm CL; 66-76 mm CL; 77-105 mm CL and ≥105 mm CL). Generally, small size classes were sampled in the shallow depth categories and larger lobsters were sampled in the deeper depth categories, which would suggest that as in the past, recent puerulus settlement has been in shallow depths. Accordingly, it would seem reasonable to conclude that it is unlikely that there has been a major shift in the depths at which pueruli are settling. However, small lobsters were sampled in low numbers in the deep water categories in this survey and this therefore does not exclude the possibility that deep water settlement may be becoming more common than in past.In terms of recommendations, more monitoring of post-puerulus/juvenile lobsters using modified commercial pots similar to those used in this study has the potential to provide inter-annual comparisons of the numbers of small size classes settling at different depths on the grounds. It is only with more data of this type over a longer time period, that it will be possible to show whether there is any indirect evidence of a shift in settlement to deeper water. Should this work continue into the future, it would be beneficial to standardize on a consistent type of modification to the commercial pots so that more reliable comparisons of the relative numbers of juvenile animals can be made between areas

Evaluating the potential use of change-in-ratio and index removal techniques for determining harvest rates and efficiency increases in the Western Rock Lobster Fishery FRDC Project 2009/019

Objectives: 1. Assess current data sources and their potential for estimating harvest rates and increases in efficiency in the western rock lobster fishery using change in ratio and index removal techniques. 2. Evaluate whether additional sources of information are needed to produce more robust estimates of harvest rate and efficiency increase. 3. Assess whether the estimates of harvest rate and fishing efficiency are reliable and could be used for the management of the western rock lobster fishery

Decision-support tools for economic optimization of Western Rock Lobster fishery

Objectives: 1. To estimate the annual catch and effort to achieve optimum economic yield 2. To evaluate intra-annual market-based management strategies. 3. To evaluate the economic effect of current and proposed management changes

Status of the Cockburn Sound Crab Fishery

Blue swimmer crabs (Portunus armatus) (formerly Portunus pelagicus; Lai et al., 2010) in Cockburn Sound, Western Australia, are the basis of an important commercial and recreational fishery close to the Perth metropolitan area with the commercial fishery achieving a peak catch of 362 t in 1997/98 and a recreational catch of about 18 t. Commercial blue swimmer crab catches declined significantly since 2000 due to low stock abundance, resulting in the closure of the fishery in December 2006

Changes in egg production of the western rock lobster (Panulirus cygnus) associated with appendage damage

Data collected during fish-ery-independent sampling programs were used to examine the impact of appendage damage (indicated by lost or regenerated legs and antennae) on the reproductive output of female western rock lobster (Panulirus cygnus). Most of the damaged females sampled had one (53%), two (27%), or three (13%) appendages that had been lost or that were regenerating. Appendage damage was associated with the reduced probability of a female developing ovigerous setae; and if setae were produced, with the reduced probability that females would produce more than one batch of eggs within a season. These effects were more pronounced as the number of damaged appendages increased. From data collected in 2002, it was estimated that the total number of eggs produced by mature females caught in the fishery was significantly reduced (P<0.001) by 3–9% when the impact of appendage damage was included