The effect of cooking on carapace length of Southern rock lobster, Jasus edwardsii (Hutton), 1875 (Decapoda, Palinuridae)

In several Australian states, the claimed potential for shrinkage of rock lobsters during cooking is a problem for enforcement of rock lobster fisheries regulations based on a minimum legal size. In Tasmania, uncertainty about the potential for shrinkage of rock lobster (Jasus edwardsii) regularly prevents prosecution. We tested the potential for shrinkage of rock lobsters by cooking 21 animals under typical industry protocols. Cooking had no statistically detectable effect on carapace length

Does pleopod setation provide a measure of maturity in female southern rock lobsters Jasus edwardsii?

Processes affecting the estimation of the size at onset of maturity (SOM) using ovigerous setae were investigated in southern rock lobsters Jasus edwardsii. Comparison of estimates of SOM based on ovigerous setae in samples collected during summer months (December-March) with those based on the presence of external eggs from winter months (June-August) indicated that ovigerous setae provide an accurate classification of maturity. Females with partially developed setation on pleopods are frequently observed in research catch-sampling projects and their maturity status was unclear. Our results show that these females with partially developed setae are most appropriately classed as immature, based on comparison between estimates of SOM determined by presence of external eggs or setae. The seasonal timing of field sampling affected estimates of SOM based on ovigerous setae, though tag-recapture data indicated that this was not associated with a loss of setae during a second annual moult. Estimates of SOM for populations of Jasus edwardsii around Tasmania can be based on maturity classification using ovigerous setae but care should be taken to ensure that seasonal timing of sampling is consistent

A novel tag-recovery model with two size classes for estimating fishing and natural mortality, with implications for the southern rock lobster (Jasus edwardsii) in Tasmania, Australia

Multi-year tag-recovery models can be used to derive estimates of age- and year-specific annual survival rates and year-specific instantaneous fishing and natural mortality rates. The latter, which are often of interest to fisheries managers, usually can only be estimated when the tag-reporting rate (lambda) and the short-term tag-induced mortality and tag-shedding rate (phi) are known a priori. We present a new multi-year tagging model that permits estimation of instantaneous mortality rates independently of philambda provided tagged animals from two adjacent size groups are released simultaneously. If the two size groups comprise animals just above and below the minimum harvestable size limit, then it is possible to estimate year-specific instantaneous fishing and natural mortality rates after 2 yr of tagging and tag-recovery. In addition to the standard assumptions of multi-year tag-recovery models, it is necessary to assume that recruited animals have equal selectivity, pre-recruited animals become fully recruited in 1 or 2 yr, and the size groups experience the same natural mortality rate. Applicability of the model to the Tasmania southern rock lobster (Jasus edwardsii) fishery is evaluated using a simulation model and parameters based on data from the lobster fishery; assumptions are likely to be met and precision should be adequate if at least 1000 animals are tagged per year in each size group. (C) 2003 International Council for the Exploration of the Sea

A Quantitative Metric to Identify Critical Elements within Seafood Supply Networks

A theoretical basis is required for comparing key features and critical elements in wild fisheries and aquaculture supply chains under a changing climate. Here we develop a new quantitative metric that is analogous to indices used to analyse food-webs and identify key species. The Supply Chain Index (SCI) identifies critical elements as those elements with large throughput rates, as well as greater connectivity. The sum of the scores for a supply chain provides a single metric that roughly captures both the resilience and connectedness of a supply chain. Standardised scores can facilitate crosscomparisons both under current conditions as well as under a changing climate. Identification of key elements along the supply chain may assist in informing adaptation strategies to reduce anticipated future risks posed by climate change. The SCI also provides information on the relative stability of different supply chains based on whether there is a fairly even spread in the individual scores of the top few key elements, compared with a more critical dependence on a few key individual supply chain elements. We use as a case study the Australian southern rock lobster Jasus edwardsii fishery, which is challenged by a number of climate change drivers such as impacts on recruitment and growth due to changes in largescale and local oceanographic features. The SCI identifies airports, processors and Chinese consumers as the key elements in the lobster supply chain that merit attention to enhance stability and potentially enable growth. We also apply the index to an additional four real-world Australian commercial fishery and two aquaculture industry supply chains to highlight the utility of a systematic method for describing supply chains. Overall, our simple methodological approach to empiricallybased supply chain research provides an objective method for comparing the resilience of supply chains and highlighting components that may be critical

Impact of lobster size on selectivity of traps for southern rock lobster (Jasus edwardsii)

Most lobster fisheries are characterized by high exploitation rates. This has led to substantial declines in the size structures of the populations over time as larger lobsters have been removed. Although both scientists and fishers have suggested that size related hierarchies could impact on lobsters entering traps, the effect of the size change on the selectivity of lobster traps as a population's size structure changes has not been investigated. This paper demonstrates that larger lobsters affect the entrapment of smaller lobsters and that this behaviour affects the selectivity of lobster traps. Both spatial and temporal (within season) factors were found to affect the selectivity plots. Spatial differences in selectivity were attributed to the broader size range of larger lobsters found in regions of faster growth. Temporal differences were attributed to the decline in larger lobsters over the course of a season caused by exploitation. There are also differences in trap selectivity between the sexes