Organic matter production of American lobsters (Homarus americanus) during impoundment in Maine,United States

Lobster impoundments are dammed coastal embayments utilised to hold American lobsters (Homarus americanus) before shipping to market. The impacts of lobster impoundments on the environment have not been previously studied. Here, the digestive functioning of American lobsters was examined to assess the quantity and quality (TVS, total volatile solids) of lobster faeces produced under the temperatures and feeding regimens these animals were subjected to during the impoundment period. Overall it was determined that quantity and quality of faeces did not differ among the experimental temperatures (5, 10, and 15°C), and that animals fed every 1–2 days produced greater quantity and quality of faeces than those fed every 3–18 days, or those animals fed less than every 18 days. As a first estimate of organic matter production in active lobster impoundments, it was calculated that a typical lobster impoundment produced 0.79 ± 0.35 (average ± 1 SD) g TVS m^‐2 day^‐1 during the impoundment period, equivalent to 3.11 ± 0.60% of the total weight of lobsters stocked into the impoundment. This level of organic matter production is below the level produced by other aquaculture operations, and that at which benthic impacts might be expected.     

Communicating climate change: Climate change risk perceptions and rock lobster fishers, Tasmania

World fisheries, already vulnerable, are under increasing pressure from the impacts of climate change. Using the Tasmanian rock lobster industry as a case study, we considered the efficacy of risk perception as a tool to inform how to communicate the science of climate change and suggestions for management in relation to development of adaptation strategies for fisheries. Fishers surveyed in this study operate in a fishery that is expected to undergo large changes as a consequence of climate change. Fishers also reported observations of similar large changes in the marine environment and lobster fishery consistent with climate change; yet most fishers surveyed expressed doubts about whether climate change was a real process. The important point for adaption of the industry to climate change is that fisher perceptions of risk tended to create barriers to acceptance of climate change as an issue. This means that there is a barrier to communication and awareness about climate change and thus a barrier to future action on the issue. Improving acceptance of climate change and thus ability to adapt will require the development of communications that are culturally appropriate and palatable to fishers. We argue that the application of social learning principles in communications about climate change may be one constructive way forward.     

Trap‐based indicators of egg production following increases in minimum legal size in Homarus americanus fisheries

Minimum legal size (MLS) is an important conservation measure in trap fisheries for Homarus americanus. MLS has increased in several management areas in the Canadian Maritimes since 1987. A key conservation objective has been to increase egg production, with predictions of the effects of MLS increase based on egg‐per‐recruit models. We evaluated whether expectations of increases in ovigerous females (OF) were realised when MLS was increased. Data were examined from at‐sea samples of the commercial trap catch from 11 ports from 1986 to 2003. OF indicators were developed based on the OF catch‐per‐unit‐effort (CPUE) of different sizes, and on the percentage (PCT) of females that were ovigerous. Because there were within‐season increases in CPUE and PCT, annual indicators were based on regressions of CPUE on day in the season. There was considerable variability in all the time series of OF annual indicators and any effects of smaller MLS increases could not be detected. Increases in OF indicators were evident in areas that undertook the largest MLS increases (6–6.5 mm CL).     

Observations of temperatures in some Rotorua district lakes

A preliminary study has been made of temperatures in some of the lakes of the Rotorua district, in the North Island of New Zealand. Seasonal and diurnal variations are discussed. Two main thermal structure types are present. One, in which stratification is irregular or absent, is present in lakes that are relatively shallow and large in area, and the other, in which there is thermal Stratification from early summer to early winter, is present in lakes that are comparatively deep and large in area or else of medium depth and size.     

Puerulus and juvenile abundance in the rock lobster Jasus edwardsii at Stewart Island,New Zealand (Note)

Settlement of puerulus‐stage New Zealand red rock lobsters (Jasus edwardsii) and abundance of the first three juvenile cohorts were measured from 1981 to 1989 near Halfmoon Bay, Stewart Island. Puerulus settlement on subtidal collectors shows great annual variation. Juvenile abundance, estimated from the number caught in annual diver collections, shows less variation. One‐year‐olds appear less vulnerable to diver sampling than older juveniles. Abundance of 2‐ and 3‐year‐olds is highly correlated with puerulus settlement 2 and 3 years previously. Survival between puerulus and 1+ stages appears to be density‐dependent, but survival of older juveniles does not. Size is inversely related to abundance in 3+ females but not in the other cohorts, suggesting density‐dependent growth between ages 2 and 3. Puerulus settlement rates and processes on shallow inshore reefs appear to be important in determining recruitment strength in this species.     

A modelled cost‐benefit analysis of hybrid PIT and conventional tagging scenarios

Tag recovery rate is an important parameter for estimating exploitation and natural mortality in fished populations. Passive integrated transponder (PIT) technology can record 100% of PIT tagged animals passing within the detection limit of a PIT tag scanner. However PIT tags and PIT tag scanners are expensive compared with conventional visual tags and PIT tags are not detectable without scanners. We used simulation to evaluate the hybrid PIT tag which has the PIT tag incorporated into a conventional tag allowing both electronic detection capability by a scanner and visual detection by fishers. Simulated estimates of the precision and accuracy of exploitation and natural death rates for two lobster fishery management regimes: a 7‐month season for both sexes and a fishery with a 10‐ and 6‐month season for males and females, respectively, were used to determine the benefit of PIT tags. For a project budget of AU#DL200,000, hybrid PIT tags and 10% of the fleet being equipped with scanners produced more precise and accurate estimates of exploitation rate and natural death rate until tag reporting rate by fishers exceeds 40% for the two‐gender management regime and 90% for the 7‐month combined sex regime. Increasing the number of scanners to 20% of the fleet resulted in fewer hybrid PIT tags being inserted for the same cost and did not improve the precision or accuracy of estimates. Increasing the number of lobsters tagged by tagging during a higher catch rate period improved the precision of exploitation and natural death rate estimates at lower tag reporting rates for the conventional tag scenario, but did not alter the tag reporting rate required to make conventional tagging more beneficial than hybrid PIT tagging. Increased tag reporting rate by the 90% of the fleet that were not equipped with scanners had no significant impact on the precision or accuracy of estimates for either management regime.     

How much spatial structure can data for rock lobster off victoria,Australia support?

Stock assessments based on fitting sex‐and size‐structured population dynamics models, combined with projections of the future implications for available biomass and egg production, currently form the basis for scientific management advice for rock lobster, Jasus edwardsii, off Victoria, Australia. Traditionally, assessments have been conducted for two “zones” (east and west) off Victoria. However, recent analyses indicate finer‐scale spatial resolution in growth and the probability of being mature as a function of size. Assessments were therefore conducted for six regions, as well as for the two conventional zones, and Bayesian model selection criteria were used to compare alternative model formulations. The results suggest that better fits to the data can be obtained by conducting assessments by region than by zone. The general qualitative conclusion of past stock assessments is that the rock lobster populations off Victoria are depleted to below the target reference point of 40% of the available biomass in 1951 and this conclusion is robust to how the data are treated spatially. However, the time‐trajectories of egg production and available biomass differ among the regions, with the areas in the centre of Victoria being more depleted than those at the extremes.     

Assessing the impacts of trawling breeding lobsters (Panulirus ornatus) on the catch of the Torres Strait lobster fishery shared between Australia and Papua New Guinea

The shared Torres Strait rock lobster (Panulirus ornatus) fishery provides important income for commercial and traditional fishers in Australia and Papua New Guinea. The lobster stock is first fished in Torres Strait by divers from both countries and then becomes vulnerable to Australian prawn trawlers, followed by Papua New Guinea trawlers during its annual breeding migration. Lobster catch sharing arrangements are governed by the Torres Strait Treaty ratified in 1985, but the sequential trawling of breeding lobsters has been controlled by bilateral agreements. A trawl ban was implemented in 1984 in both countries to conserve the breeding stock, but some trawling has been conducted in the Gulf of Papua since then and there is renewed interest in Papua New Guinea to resume trawling. To evaluate the impact of trawling migratory breeding lobsters on the lobster fishery, a model that combines a cohort depletion model with a stock recruitment relationship was developed in this study. The model showed that when the fishery is fully or over‐exploited by the dive fishery, trawling breeding lobsters would reduce both the spawning stock and the total catch of the fishery. The reduction in catch would increase with increasing fishing mortality. If trawling occurred on the Papua New Guinea side only, a redistribution of catch between Australia and Papua New Guinea would result in a small gain in catch for Papua New Guinea at the expense of the Australian dive fishery. But when fishing mortality reaches a certain level, any trawling in any country will incur catch loss to both countries. For the long‐term sustainability and maximum production of the fishery, regulations should be implemented in both countries under a co‐management scheme of a shared fish stock.