C Gardner

Effect of photoperiod and light intensity on survival, development and cannibalism of larvae of the Australian giant crab Pseudocarcinus gigas (Lamarck)

Pseudocarcinus gigas larvae were reared to megalopa under two light intensities 2 and 500 . . lux in five photoperiod regimes 0, 6, 12, 18, and 24 h light . Survival was not significantly . affected by photoperiod or light intensity P) 0.05 , although other effects were observed which are discussed in relation to swimming activity and feeding. Larvae had shorter intermoult duration in treatments with longer photoperiods and brighter light with most rapid development to . . megalopa in the continuous light, 500 lux treatment 49.2 d . Size measured as telson width of stage 4 zoeas was affected by photoperiod with smallest zoeas in the continuously dark treatment, whereas all other treatments were similar. Cannibalism was strongly influenced by lighting with greater damage to the dorsal spine occurring with increasing photoperiod and also in dimmer 2 . lux treatments. Lowest incidence of cannibalism was observed in continuous darkness. Viability of larvae after metamorphosis to megalopa was variable and no treatment effect was observed although viability was lowest in the two continuous light treatments. Results of this trial indicate that continuous light or dark regimes should be avoided. Optimal light intensity for culture was less clear and is discussed in relation to intermoult duration and cannibalism. q 1998 Elsevier Science B.V. All rights reserved.

Relationship between settlement of southern rock lobster pueruli, Jasus edwardsii, and recruitment to the fishery in Tasmania, Australia

Puerulus catches on artificial collectors were measured monthly at four sites around Tasmania from 1991 to April 2000, with the aim of predicting future changes in recruitment to the fishery. Support for the potential of catch-rate prediction in Tasmania was provided at the two sites that have overlap of several years between indices of puerulus settlement and indices of the abundance of recruits to the fishery. At Bicheno, on the northeast coast, correlations between annual puerulus index and commercial catch rates were highly significant, with a lag of 5 years (P< 0.01). Similar interannual trends in puerulus index and estimates from a stock-assessment model of the biomass of recruits to the fishery provided additional support for a link with puerulus index. A 5-fold interannual variation in puerulus index detected at Bicheno, with a peak in 1995, was preceded by 3 years of relatively low puerulus catch. The peak in puerulus index appears to lead to an increase in the abundance of sublegal males in research sampling 3 years later. Correlation between annual measures of puerulus index and catch rate also appeared significant at King Island (P= 0.06) although data at this site had less contrast.

Colour variation in the southern rock lobster Jasus edwardsii and its economic impact on the commercial industry

Abstract Southern rock lobster Jasus edwardsii varies in shell coloration throughout southern Australia. Predominantly exported as a live product to Asian markets, price is influenced by colour with prices higher for dark red than paler coloured lobsters, which are discounted. This paper explores spatial and depth variation in shell colour for the Tasmanian, South Australian and Victorian fisheries using catch sampling data. The proportion of red lobsters decreased with depth and was prevalent at depths less than 30 m, whereas paler coloured lobsters dominated the deeper depth ranges. The depth of transition where 50% of lobsters were classified as red showed a weak trend of increase with latitude from southern Tasmania to northern South Australia. Under quota management, lobster colour was a significant driver of fleet dynamics as fishers target areas of high price per unit. Consequently, catches of pale lobsters from greater depths remain low despite the high catch rates in these areas. The colour price differential varies seasonally (higher in summer) so fishers increase supply of pale lobsters during winter. Discounting on colour equates to AUS

Effect of size on reproductive output of giant crabs Pseudocarcinus gigas (Lamarck): Oziidae

6.67 million/year for the Tasmanian Fishery alone, which indicates value from management or marketina research to reduce discountina.

The Good, the Bad and the Recovery in an Assisted Migration

Fecundity and egg size of giant crabs (Pseudocarcinus gigas) were determined from egg masses of 162 crabs sampled from three sites in south-eastern Australia: western Victoria, western Tasmania and eastern Tasmania. Crabs ranged in carapace length from 126 to 220 mm and egg number ranged from 830000 to 2500000. Egg number and egg size increased with size of female. There appeared to be a decline in number of eggs and size of eggs with successive broods produced between moults. Sampling locality appeared to have little effect on reproductive output. Regression of an allometric model of log egg number to log crab size had a slope of 1.76 which was significantly less than 3.0. This indicates there is not a simple volumetric relationship between the variables, which would tend to occur if increasing fecundity with female size was a simple function of increased body space available for ovarian development. This pattern appeared to be a function of decreasing egg number and size with successive broods, and the trend of increasing egg size with female size.

Stock enhancement of rock lobsters (Jasus edwardsii) : timing of predation on naïve juvenile lobsters immediately after release

Background Assisted migration or translocation of species to ameliorate effects of habitat loss or changing environment is currently under scrutiny as a conservation tool. A large scale experiment of assisted migration over hundreds of kilometres was tested on a morph from a commercial fishery of southern rock lobster Jasus edwardsii, to enhance depleted populations, improve the yield and sustainability of the fishery, and test resilience to a changing climate. Methodology and Principal Findings Approximately 10,000 lower-valued, pale-coloured lobsters were moved from deep water to inshore sites (2 in Tasmania [TAS] and 2 in South Australia [SA]) where the high-value, red morph occurs. In TAS this was a northwards movement of 1° latitude. Growth was measured only in TAS lobsters, and reproductive status was recorded in lobsters from all locations. Pale females (TAS) grew 4 times faster than resident pale lobsters from the original site and twice as fast as red lobsters at their new location. Approximately 30% of translocated pale lobsters deferred reproduction for one year after release (SA and TAS), and grew around 1 mm yr−1 less compared to translocated pale lobsters that did not defer reproduction. In spite of this stress response to translocation, females that deferred reproduction still grew 2–6 mm yr−1 more than lobsters at the source site. Lobsters have isometric growth whereby volume increases as a cube of length. Consequently despite the one-year hiatus in reproduction, increased growth increases fecundity of translocated lobsters, as the increase in size provided a larger volume for producing and incubating eggs in future years. Conclusions and Significance Assisted migration improved egg production and growth, despite a temporary stress response, and offers a tool to improve the production, sustainability and resilience of the fishery.

When is spillover from marine reserves likely to benefit fisheries

Abstract The success of enhancement programmes hinges on the survival of released animals. One factor greatly influencing short‐term survival of reseeded lobsters is the timing and intensity of predation relative to the time of release. The activity and abundance of predators varies over daily, seasonal, and annual scales and knowing the best time to release juveniles will minimise mortality. We used chronographic tethering devices and remote video equipment at 10 sites near Wellington, New Zealand and Hobart, Tasmania, Australia, to assess the relative timing and intensity of predation for released lobsters. Our studies showed that predation was greatest within the first 2 h after release (χ 2 = 60.425, d.f. = 9, P < 0.001) suggesting that the disturbance associated with the release itself may draw the unwanted attention of predators. Relative predation rates also peaked on each of the following two mornings, possibly because of the emergence of daytime predators. The video footage obtained at the Tasmanian sites revealed that most predation was by fish (46%), but surprisingly, cannibalism comprised 16% of predation events. The limitations of tethering as a method are discussed in numerous reviews but proved useful as a relative measure for these highly mobile and cryptic animals. Further consideration needs to be given to methods of release that minimise mortality of recently seeded lobsters.

The Economic Feasibility of Translocating Rock Lobsters to Increase Yield

The net movement of individuals from marine reserves (also known as no-take marine protected areas) to the remaining fishing grounds is known as spillover and is frequently used to promote reserves to fishers on the grounds that it will benefit fisheries. Here we consider how mismanaged a fishery must be before spillover from a reserve is able to provide a net benefit for a fishery. For our model fishery, density of the species being harvested becomes higher in the reserve than in the fished area but the reduction in the density and yield of the fished area was such that the net effect of the closure was negative, except when the fishery was mismanaged. The extent to which effort had to exceed traditional management targets before reserves led to a spillover benefit varied with rates of growth and movement of the model species. In general, for well-managed fisheries, the loss of yield from the use of reserves was less for species with greater movement and slower growth. The spillover benefit became more pronounced with increasing mis-management of the stocks remaining available to the fishery. This model-based result is consistent with the literature of field-based research where a spillover benefit from reserves has only been detected when the fishery is highly depleted, often where traditional fisheries management controls are absent. We conclude that reserves in jurisdictions with well-managed fisheries are unlikely to provide a net spillover benefit.

Biological Modeling of Translocation as a Management Tool for a Rock Lobster Fishery

Translocation of undersize rock lobsters Jasus edwardsii from low-growth to high-growth areas has been proposed as a method to improve yield and marketability. The economic feasibility of these operations was examined for translocations by either charter vessels or by fishers retaining their sub-legal catch and releasing these on their return trip to port. Benefit was quantified by the increase in revenue relative to leaving lobsters at their original site, less cost for translocating lobsters. Scenarios were considered feasible when costs per kg gain in yield were below that for quota leased through the market. Lower cost fisher translocations appeared feasible except for short distance translocations from deep to shallow water in the same region. Greatest net benefit occurred from long distance translocations between regions with extreme differences in growth (from SW to NW Tasmania). These operations required vessel charter and led to a net state benefit of Australian169,000 per 5-tonne trip, with internal rates of return approaching 400%. Cost per kg gain in catch for these operations was estimated at less than A3/kg and thus substantially less than the current lease price of around A16/kg. The apparent economic feasibility of translocation provides support for pilot-scale trials.

Environmental effects on fished lobsters and crabs

Translocation is a form of sea ranching and involves shifting animals between regions to increase yield or to address sustainability issues. We used a sex and size structured model with yearly time steps to examine the use of translocation for management of the Tasmanian rock lobster (Jasus edwardsii) fishery, which is a fishery characterized by spatial heterogeneity in biology and depletion through fishing. Cohorts of undersize lobsters were translocated from four sites of origin to four release sites to explore outcomes under a range of growth rates. Results of translocations were contrasted against estimated yield and egg production if the lobsters had been left at their original site. Gains in yield of greater than 100% of existing yield appear possible through many scenarios, although gains were largest when distances between sites were greatest (from SW to NW Tasmania). Short-distance translocations from deep to shallow water have been proposed to alter market traits of lobsters, but gains in yield from this type of operation appear trivial. Egg production was increased at the release site for all scenarios, indicating that translocation could complement the current policy of rebuilding northern egg production. Translocation appears to offer an alternative management option for increasing yield and could be integrated with other spatial management tools such as regional size limits.