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Selection of traps tested for capture of juvenile lobsters: A -Opera House trap; B -Polynesian fish trap; C -Square crab trap; D -modified starfish trap; E -meshed stick lobster pot; F -dome trap
Source publication
The potential benefits from reseeding juvenile rock lobsters back to the wild are broad. In the
short term, it will allow the commencement of commercial rock lobster aquaculture operations
in Tasmania through the harvest of puerulus (first settling stage of juvenile rock lobsters). A
concern with the harvest of puerulus is that catch of rock lobste...
Contexts in source publication
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... lobsters from release 1 were tracked throughout the 14 days of the trial, however, not all lobsters were located on each day. One control lobster (relocated) was detected by the boat mounted receiver but not cited by the divers on days 3 or 4. One on-grown lobster was not located for 2 days after release, but was relocated 140m due west of the release site on day 3 ( Figure 10). This lobster had moved over approximately 100m of unstructured sand habitat, and settled in an area of reef cohabited by wild lobsters. ...
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... from the 3 treatments were pooled to calculate the optimal search area for re-sighting visually tagged lobsters released in the reseeding trial ( Figure 11). By superimposing a grid of varying size onto the plot of lobster positions, a search area that would give a good coverage of predicted movement without excess effort could be determined. ...
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... analysis indicated that the most efficient search area is a 32x32 m square, which was subsequently adopted for the large scale release experiment. Width of square (m) Percent of sonic tagged individuals Figure 11. Estimation of appropriate experimental square size for isolation of survival and movement with the Jackson Square Technique. ...
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... 3 times as many on-grown lobsters were released as control lobsters (Table 1). However, by the time of the first survey within the 32x32 m grid, the resighting ratio was about 1.5:1, and remained at about 1:1 inside this area from the second survey until the completion of field work ( Figure 13). This indicates that there was a group affe ct on the resighting of juveniles lobsters -that is, the ongrown animals were less likely to be resighted. ...
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... attempted to assess if movement of tagged lobsters within the Jackson square grid indicated any group effect on movement patterns -that is, does greater movement by the ongrown animals account for the apparent decline in their abundance seen in Figure 13 ? There appeared to be little difference in rates of movement between the treatment groups inside the Jackson Square (Figure 14). ...
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... attempted to assess if movement of tagged lobsters within the Jackson square grid indicated any group effect on movement patterns -that is, does greater movement by the ongrown animals account for the apparent decline in their abundance seen in Figure 13 ? There appeared to be little difference in rates of movement between the treatment groups inside the Jackson Square (Figure 14). Resighting data from inside the Jackson square also indicated that movement was generally small with most lobsters sighted on consecutive days moving only a short distance to an adjacent grid square. ...
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... the final resighting survey by divers, transect searches were performed to a distance of 800m from the release site. As distance from the release site increased, the proportion of on- grown lobsters resighted by divers increased (Figure 15). Interpolation of this plot suggests that beyond a distance of 180m from the release site, the proportion of on-grown lobsters sighted was higher than initially released. ...
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... lobsters appear to have moved a distance greater than 2 grid squares. n=28 Figure 15. Comparison of movement of control and on-grown rock lobsters. ...
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... density dependent increase in movement was supported by comparison of movement patterns of acoustic tagged lobsters released before and concurrently with the large scale release. Move ments of the second group tended to be higher throughout the 17 day duration of the trial (Figure 16), with the exception of the first 4 days, where variation was very high. ...
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... a difference in resighting rate was observed between antennal tagged lobsters released in different densities on 2 consecutive days (494 on day 1; 86 on day 2). A consistently higher percentage of lobsters from the second release were resighted within the Jackson square grid (Figure 17). While not conclusive, a plausible explanation is greater movement away from the site by lobsters reseeded at a higher density. ...
Context 11
... there appears to evidence of a density dependent increase in movement of both groups, this does not explain the greater movement of ongrown juveniles relative to wild controls ( Figure 15). We expected the opposite result as ongrown animals had been held in tanks at high density so we expected them to be more tolerant of higher density. ...
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... this presentation of variation is not entirely appropriate as raw movement data are not normal, the plot is only intended to indicate similarity of general patterns with antennal tag resighting data -the effect of release group was not significant. resighting opportunity Percentage animals resighted Release1 (n=494) Release2 (n=86) Figure 17. Effect of release group on resighting probability within release site only (ie excluding resights from neighbouring reef). ...
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... test if reseeded lobsters were feeding, we recaptured all acoustic tagged animals from release 1 on the morning of day 14 of the study, plus an additional 9 untagged wild lobsters. Stomachs were removed, and a gut fullness index recorded on the basis of ratio of weight of stomach including contents to stomach without contents ( Figure 18). While gut fullness indices were variable, those of on-grown lobsters were within the range of those of wild lobsters, and the presence of acoustic tags did not appear to inhibit feeding. ...
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... single local control lobster (acoustic tagged wild juvenile from the same reef) had an empty stomach, and was in pre- moult condition. Re-seeded Figure 18. Gut fullness indices of recaptured acoustic tagged lobsters and wild lobsters caught concurrently. ...
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... Jackson Square technique relies on the assumption that emigration rates from a large square (site) will less than from a smaller square (site), and that this difference will be proportional to the size and geometry of the two areas ( Figure 19). Jackson's (1939) method can remove the bias of emigration in the calculation of survival and also provides an estimate of emigration which can be of interest. ...
Context 16
... i rs = the probability of an animal alive in strata r in time i is alive and in strata s at time i+1. This is illustrated in Figure 21. While the estimation of a parameter that combines movement and survival as illustrated in Figure 21 is useful, for the study of rock lobster reseeding we were also interested in separating these two effects. ...
Context 17
... is illustrated in Figure 21. While the estimation of a parameter that combines movement and survival as illustrated in Figure 21 is useful, for the study of rock lobster reseeding we were also interested in separating these two effects. That is, we aimed to obtain separate estimates of movement and survival. ...
Citations
... While there are no examples of the release of hatchery-reared spiny lobster juveniles, wild-caught pueruli of Jasus edwardsii were cultured in Tasmania, Australia, for a year and then used in experimental releases. These lobsters showed their larger size greatly improved their survival once released back into the wild (Gardner et al. 2000). However, predation at the time of release needs to be carefully managed because of the increased concentration of released individuals and the naïve behavior of the captive-reared juveniles toward predators (Oliver et al. , 2008. ...
Marine lobsters include some of the most highly prized and valuable seafood species in the world. Accessible wild populations of edible lobster species are under increasing pressure from harvesting, habitat loss, disease, pollution and climate change. To provide an alternative supply, there have been extensive efforts to develop aquaculture methods for many species of marine lobsters, but with slow progress. A range of unfavorable biological attributes of marine lobsters has constrained their development for aquaculture, including complex life cycles, low fecundity, extended larval periods, slow growth, and cannibalism. A lack of knowledge of aspects of the fundamental biology of many species has also made it challenging to advance aquaculture techniques. Currently, the only extensive commercial aquaculture of marine lobsters occurs in Vietnam, with annual production of well over 1,000 t of spiny lobsters. This involves the wild capture and mariculture of early juveniles of several species of spiny lobsters in simple floating sea cages and feeding them on freshly caught marine life, mostly small coastal fish and benthic invertebrates. The success of this apparently simple technology indicates the opportunity for increased aquaculture production as soon as the recent advances in larval culture of spiny (Palinuridae) and slipper (Scyllaridae) lobsters can provide a large and sustainable source of juveniles. While viable larval culture methods for the American and European clawed lobsters (Homaridae) have been available for some time, more recent advances with compartmentalized land- and sea-based culture systems show promise in overcoming the cannibalistic behavior of these species, an essential step toward developing commercially viable aquaculture. The likely emergence of large-scale commercial aquaculture of marine lobsters in the next decade has the potential to provide an alternative supply of lobsters into global seafood markets, with the prospect of relieving fishing pressure on wild populations of marine lobsters.
... This then provides a source of juveniles that can be on-grown to a size where natural mortality is lower. This approach has been applied in Jasus edwardsii which were cultured for a year before release and had substantially improved survival (Gardner et al., 2000;Mills et al., 2005;Gardner et al., 2006a;Mills et al., 2006). ...
Enhancement of lobster fisheries has the use of a range of systems over the last 150 years. Attempts to create new fisheries resources by translocating lobsters beyond their natural range have been largely unsuccessful. Although occasional reports of Homarus americanus in European waters occurred since the 1990s, no self-producing populations have been documented. The release of hatchery reared H. americanus and H. gammarus juveniles for recovery of depleted stocks and enhancement of fisheries has had a long history with most recent activity underway in Norway, the UK and Ireland. Research scale enhancement of spiny lobsters has also occurred using juveniles on-grown from wild-sourced puerulus. Success in these operations has relied on understanding processes affecting post-release survival and modifications to the release operations. Enhancements also occur through moving lobsters that are below harvestable size within their natural range. This improves market traits and production by moving lobsters to areas of higher growth. This review explores the performance of lobster enhancement operations through case studies, including one on Jasus edwardsii, and also the general principles that underpin enhancement, such as the need for monitoring and evaluation of economic feasibility.
... This then provides a source of juveniles that can be on-grown to a size where natural mortality is lower. This approach has been applied in Jasus edwardsii which were cultured for a year before release and had substantially improved survival (Gardner et al., 2000;Mills et al., 2005;Gardner et al., 2006a;Mills et al., 2006). ...
Enhancement of lobster fisheries has used a range of systems over the last 150 years. Attempts to create new fisheries resources by translocating lobsters beyond their natural range have been largely unsuccessful. The exception is Homarus americanus introductions to Europe, which have now created concern around possible ecological consequences. The release of hatchery reared H. americanus and H. gammarus juveniles for recovery of depleted stocks and enhancement of fisheries has had a long history with most recent activity underway in Norway, the UK and Ireland. Research scale enhancement of spiny lobsters has also occurred using juveniles ongrown from wild-sourced puerulus. Success in these operations has relied on understanding processes affecting post-release survival and modifications to the release operations. Enhancements also occur through moving lobsters that are below harvestable size within their natural range. This improves market traits and production by moving lobsters to areas of higher growth. This review explores the performance of lobster enhancement operations through case studies and also the general principles that underpin enhancement, such as the need for monitoring and evaluation of economic feasibility.
... Scuba divers collected wild lobsters from the study site by hand. Despite extensive trials (Gardner et al., 2000), no effective trapping method for juvenile J. edwardsii has been identified. Although divers targeted lobsters in the same size range as the naı¨ve lobsters to be released, lobsters up to 68mm CL were collected and retained to increase the total number of wild lobsters available for release. ...
Using multistate Arnson–Schwartz (AS) mark-recapture models, we show that naïve (captive reared) juvenile southern rock lobsters (Jasus edwardsii, Hutton 1875) survived as well as wild-caught lobsters when released to an area of coastal reef. Lobsters captured as pueruli were ongrown in tanks for 12 to 18 months where they were fed to satiation in the absence of predators. Lobsters were marked with antennal tags each carrying a unique code, and released to coastal reef along with tagged wild-caught lobsters of similar size. During 8 dive surveys of the release reef and 3 surveys of adjacent reefs over a 28 day period, divers resighted 40.3% of the naïve lobsters and 70.2% of the wild lobsters. We show that this discrepancy is a function of differing movement rates and spatial differences in resighting probability. The probability of naïve lobsters moving from the release reef to adjacent areas in the first 4 days post-release (0.72 ± 0.04 S.E.) was almost twice that of wild-caught lobsters (0.38 ± 0.08 S.E.). This behavioural difference did not influence daily apparent survival (0.98 ± 0.016 S.E.), which was constant between groups and over time. Our results are encouraging for the potential of enhancing spiny lobster stocks by releasing juveniles, and demonstrate the utility of AS mark-recapture models as a tool for evaluating medium-term survival of mobile marine species.
... In Tasmania, permits for harvesting wild pueruli have been issued on the condition that a proportion of the juveniles be released after 1 year to compensate for their removal from the wild stocks. When this proportion is greater than natural survival over the same period, a level of fishery enhancement is achieved (Gardner et al. 2000). ...
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= 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.
... On the other hand, where stocks are not so depressed, harvesting of reduced numbers of adults, combined with farming of juveniles and releases of a portion of the cultured young in the wild, should increase spawning biomass and pave the way for increased productivity. Elements of this process can be found in the Tasmanian proposal for lobster pueruli aquaculture, where a proportion of reared juveniles are to be introduced into prime habitats with low larval supplies, thus enhancing natural productivity (Gardner et al. 2000). ...
This book contains 17 chapters. Topics covered are: management of marine aquaculture: the sustainability challenge; marine mammals and aquaculture: conflicts and potential resolutions; recreational fishing and aquaculture: throwing a line into the pond; aquaculture: opportunity of threat to traditional capture fishermen; advances in marine stock enhancement: shifting emphasis to theory and accountability; aquatic polyculture and balanced ecosystem management: new paradigms for seafood production; the role of marine aquaculture facilities as habitats and ecosystems; mangroves and coastal aquaculture; environmental effects associated with marine netpen waste with emphasis on salmon farming in the Pacific Northwest; issues associated with non-indigenous species in marine aquaculture; genetic changes in marine aquaculture species and the potential for impacts on natural populations; what role does genetics play in responsible aquaculture; understanding the interaction of extractive and fed aquaculture using ecosystem modelling; shrimp farm effluents; fish meal: historical uses, production trends and future outlook for sustainable supplies; the use of wild-caught juveniles in coastal aquaculture and its application to coral reef fishes; contending with criticism: sensible responses in an age of advocacy.
... If suitable locations are identified in the future, the reseeding of juveniles would need to be considered to compensate for the loss of recruitment into the fishery. It has been suggested that the loss of pueruli collected for culture to the commercial industry can be fully compensated for by releasing the equivalent number of juveniles that would have survived in natural conditions after a year of culture ( Gardner et al., 2000). The economic impact on the feasibility of the rock lobster farm when reseeding juveniles to the wild would therefore require further investigation. ...
The diversification of current aquaculture practise in South Africa is crucial for the future development of the industry. The rock lobster, Jasus lalandii has been identified as a possible candidate species for shore based culture in systems similar to those used for abalone farming. Reduced Total Allowable Catch (TAC's) and an increased minimum legal size were implemented as management strategies to relieve fishing pressure on natural stocks of J. lalandii, and in turn led to increased market demand and a possible niche for farmed lobsters. High puerulus settlement along the Namibian coast, together with other favourable aquaculture attributes, indicate that the commercial grow out of wild harvested juveniles could be feasible. The aim of study was to investigate the feasibility of growing out rock lobsters in shore based systems in Namibia and South Africa. The experimental objectives of the project were to investigate the nutritional requirements, as well as the effect of stocking density and tank design on growth and survival of J. lalandii. The economic viability of shore based rock lobster farming was then evaluated based on the experimental results and typical capital requirements of an abalone farm in South Africa. Puerulus and early juvenile rock lobsters were collected in Luderitz, Namibia and transported to HIK Abalone Farm in Hermanus, South Africa where they were acclimated in black fibre glass tanks in a flow through system. The pueruli were stocked at 50, 75, 100 and 125/m² and early juveniles at 20, 30, 40 and 50/m² to test the effect of density on growth and survival. A comparative dietary study with both size classes was conducted using a mussel diet (Choromytilus meridionalis and Mytilus galloprovincialis), a commercial shrimp feed diet and a rotational diet comprising both mussels and shrimp feed. Tanks provided with “v-shaped” asbestos hides, PVC hides and no hides were compared to test the effect on growth rate and survival of pueruli. All treatments were conducted in triplicate. Temperatures were recorded twice daily while water quality parameters were tested every second week. The results indicate that density had a significant effect on growth and survival on post-pueruli. An initial stocking density of 75 post-pueruli/m² is regarded as optimal both in terms of the growth rate and biomass production per tank. No differences in growth and survival rates were attained in the early juvenile size class. This indicates that higher densities can be used to rear juvenile J. lalandii. No significant differences were obtained in growth rate when reared under different hide conditions although asbestos hides yielded significantly higher survival rates (93.3 %) compared to the tanks provided with PVC hides (74.04 %) and no hides (77.8 %, p≤0.05). As a result of the high survival rate observed in tanks provided with “V-shaped” asbestos hides, these tanks also yielded higher biomass production per tank (297.8 grams) compared to the tanks provided with PVC hides and no hides (261.09 and 260.5 grams respectively). In the diet trials, growth rates of post pueruli and juvenile lobsters fed the mussel and rotational (mussel and shrimp feed) diets did not differ significantly, however, growth rates of lobsters fed the shrimp feed only diet was significantly lower than both the mussel and rotational diets (p≤0.05). Lobsters fed the mussel diet yielded significantly higher survival rates compared to lobsters fed either the rotational diet or shrimp feed diet only. An imbalance in the fatty acid profile of the shrimp feed could have been a major contributing factor to the poor growth and survival in lobsters fed the shrimp feed only diet as the level of linoleic acid (LOA) was exceptionally high resulting in a high (n -6):(n-3) ratio (1.01) compared to the mussel and rotational diets (0.17 and 0.56 respectively). The low level of arachidonic acid (ARA) in the shrimp feed diet could be a further contributing factor explaning for the poor growth and survival of juvenile rock lobsters. An economic feasibility study was conducted at the end of the experimental phase by modelling a hypothetical shore based rock lobster farm. A projection of production costs and revenues was based on the typical costs of a shore based abalone farm and the current market prices for wild harvested J. lalandii. The economic viability was evaluated using benefit-cost ratios, payback period, internal rate of return and breakeven analysis. Sensitivity analyses revealed that the projected lobster growth and survival rates were the main biological factors influencing the economic feasibility of the hypothetical rock lobster farm. An assumed four year grow out period at a low stocking density yielded more lucrative internal rate of return (IRR), benefit-cost ratio, payback period and net present values (NPV) than a five year grow out period at a high density. The four year grow out scenario proved to be more robust to the fluctuating Rand/US$ exchange rate and could accommodate a lower lobster survival rate. Results presented in this study indicate that rock lobster farming is a marginal commercial prospect based on current production performance and costs. Further research to develop effective puerulus collection techniques as well as to make lobster grow out technology more cost effective is required.
The release of juvenile lobsters for enhancement purposes was initiated in Tasmania on a pilot scale as part of puerulus harvest operations. The puerulus stage of southern rock lobsters is reached after an 18-24 month larval life following which puerulus can be captured on collectors that mimic natural reef. After a further 12 months in culture, juvenile southern rock lobsters grow to around 35 g, which is the size of animals released in this study. This around the size at which southern rock lobsters begin to become sociable and cohabit in dens. It is believed that the release of juveniles at this size allows them to avoid the period of high mortality that occurs during the first 12 months with natural survival during this period estimated at less than 10%.
This study aimed to develop release protocols for rock lobster enhancement operations that optimised survival. Part of this research involved large-scale releases that simulated release operations conducted for enhancement purposes. Research was conducted in both Tasmania and New Zealand to utilise expertise across the broad range of behavioural and ecological processes that affect survival of juvenile lobsters.
Release protocols to minimise mortality
An initial concern was that the altered behaviour of juvenile lobsters reared in tanks would affect their survival after release. In particular, juveniles cultured in tanks tend to emerge from shelter during the day and forage in open areas. This behaviour does not occur in the field and was considered to represent a probable risk of increased predation. This issue was addressed in two ways. First, we examined methods for initiating more natural behavioural patterns of lobsters in tanks during the grow-out phase. Secondly, we examined the behaviour of “naïve” lobsters following release onto natural reef: did they respond normally to predators?
We found that the foraging and emergence patterns of juvenile lobsters in captivity could be made equivalent to natural patterns by the controlled addition of a predator, such as a fish. This acclimatisation to a predator is used widely in enhancement operations for finfish where survival after release is subsequently improved. Although
the addition of a predator produced normal foraging behaviour, it also reduced growth and condition as juveniles spent more time sheltering rather than feeding. A more appropriate solution for culture situations was to supply feed to lobsters at dusk. This simple change in husbandry could be achieved using automatic feeders that dispensed food at dusk and was highly effective for inducing normal foraging behaviour.
Although it was possible to modify the behaviour of juveniles, subsequent experiments demonstrated that these steps are not necessary for enhancement operations. Key findings from video observations of released juveniles were that juveniles grown in captivity appear to retain an innate ability to recognise and respond appropriately to predators. This is an encouraging result for enhancement operations and also suggests that juvenile lobsters do not need to be habituated to predators prior to release. The risk of cannibalism in culture may help in maintaining appropriate predator avoidance behaviour.
The timing of predation was examined in both Tasmania and New Zealand to identify the times of day that should be avoided during release operations. This issue was examined in two ways. Lobsters were tethered to stop watches so that the timing of predation was recorded automatically. In addition, released juveniles were monitored by remote video with infra-red illumination that was invisible to both juvenile lobsters and potential predators. Both methods confirmed that mortality of released juveniles was highest in the first two hours after release and around dawn. Best survival was between midnight and dawn. Consequently, it is recommended that release operations aim to release animals around midnight.
Releases of juvenile lobsters in enhancement operations in Europe have been impacted by high predation during the release of juveniles. We examined this issue using diver and camera observations of pilot-scale releases. In Tasmania, these showed that while predation occasionally occurred immediately following release, the process of releasing lobsters did not attract large numbers of predators. This was caused by behaviour of the dominant daytime predator in Tasmania: male blue-throated wrasse (Notolabrus tetricus). As these species are fiercely territorial, pilot scale releases generally occurred within the range of only 1 or 2 fish, resulting in low predation pressure from these species at the time of release. These fish often actively excluded other predators from the release site to maintain their territory. Predation during daylight releases in New Zealand had the potential to be higher than in Tasmania because of the presence of a small diver-positive wrasse (spotties; Notolabrus celiodotus) that schooled when they attacked juvenile lobsters.
One method for improving survival of lobsters at release, if this was of concern, is to place the animals inside cages that exclude predators so that they can find shelters without risk of mortality. We released lobsters into mesh cages of 3m x 3m placed on reef for 48 h. These increased the number of lobsters resighted in later dive surveys, although acoustic tracking suggested that this was largely due to suppression of a ‘flight’ response rather than a decrease in mortality. Lobsters that had been caged for 48 h were less likely to move beyond the area searched by divers than uncaged lobsters. The usefulness of cages is dependent on habitat complexity. Where there are insufficient hides for all lobsters within the caged area (likely in commercial-scale releases), the effectiveness of cages is diminished. This is because those lobsters without suitable shelters tend to disperse widely as soon as the cage is removed. Given the apparently high survival of lobsters released directly by divers, the prescription that cages be used for commercial release would be an extremely conservative move likely to incur considerable costs to operators.
During the planning of commercial releases of juveniles in Tasmania there was concern that survival may be lower in some seasons than others. We compared survival of juveniles released in winter and summer at sites in 2 bioregions in Tasmania. Sites in different bioregions were selected to provide diversity of potential predators. At the southern site (Adventure Bay) there was no seasonal difference in predation rate. At the northern site (Rheban Beach) predation pressure was significantly higher in summer. The conclusion for these experiments is that winter releases are preferred.
In summary, optimal release protocols can be based on a few simple elements. Optimal timing for releases appeared to be late in the night during winter months. Juveniles reared in captivity appeared to respond appropriately to predators after release. A highly conservative release strategy would include conditioning of juveniles to nocturnal foraging prior to release and caging of animals on complex reef for a period of 48 h before release.
Selecting release (micro)habitats for optimising the benefit of enhancement operations
Another objective of the project was to provide recommendations on release habitats. This involved comparing the survival of juveniles released onto a range of habitats. Note that we only selected healthy rocky reef ecosystems for release sites, as this was a more realistic scenario for future commercial-scale releases. A large amount of preliminary research was involved in the development and testing of methods to determine differences in survival between habitats.
We examined several methods to compare survival between habitats. Each had varying levels of complexity, expense and power. These techniques were: (1) Baited video drops; (2) Tethering trials; and (3) Pilot-scale releases. For methods 1 and 2 it was necessary to know the identity of predators, which we established using a remote video system with infrared illumination.
The baited underwater video technique was a possible method for testing sites prior to large scale releases. It is a quick and simple method involving dropping a frame with a video and bait from a vessel, and recording the number of fish predators attracted within a period of time, say 15 minutes. Although this proved to be effective for assessing the abundance of finfish predators, it failed to measure the total abundance of predators. This was because a high proportion of predation events were by octopus. Consequently, we failed to detect any correlations between predation of juvenile lobsters and fish abundance measured by baited video.
Another method to compare between sites was the measurement of survival of juvenile lobsters that were tethered so that they couldn’t roam large distances away from the site of release. Video observations of these lobsters suggested caution in the interpretation of tethering results. Tethered lobsters were monitored by video at 4 sites in Tasmania. Surprisingly, large lobsters and a crab species (Nectocarcinus tuberculosis) were found to be significant predators of tethered juvenile lobsters. Validation trials in a mesocosm or ‘artificial reef’ showed that this was largely an artefact of tethering – large lobsters and crabs were generally unable to capture untethered lobsters. This implies that for tethering results to be used to compare habitat types, there must also be video observations to identify the predator.
In selecting sites for tethering and pilot-scale release trials we targeted only sites that we believed appropriate for releases. Sites were selected on the basis of the presence of wild juvenile lobsters, an obvious abundance of appropriate sized shelters for the size of lobster being released and a moderate to high algal density to provide cover when lobsters were first released. At each site, microhabitat data including rugosity, algal density and species abundance, den size and distance from the reef edge were collected. Variability in predation pressure between sites as measured by tethering was low, and few correlations were found with microhabitat variables. These results, combined with high apparent survival of lobsters, suggest that our selection criteria for sites were appropriate and that there is little to be gained from the added expense of microhabitat surveys when selecting sites for commercial release.
One aspect that appears to provide guidance in the selection of habitat for releases is the effect of reef size. Acoustic tracking and modelling of movement from pilot-scale releases revealed that lobsters exhibit a ‘flight’ response when first released. During this period they do not respond to habitat boundaries, and are likely to move onto sand. Apparently reduced survival at one pilot-scale release site (Adventure Bay), where the reef was small and isolated from other areas of reef, appeared to be due to lobsters leaving the reef during this ‘flight’ response period. Diver observations at that site confirmed this with some juveniles found exposed in areas of open sand on the day after the release. We propose that lobsters should be released on large areas of reef rather than isolated or patch reef. If the area of reef available for releases is limited, seafloor cages could be employed to suppress the ‘flight’ response.
In summary, suitable release habitats can be adequately selected by divers on the basis of presence of other juveniles, abundance of shelter, and good algal cover without the need for expensive surveys of potential predation rates. Large-scale releases should be conducted on large areas of contiguous reef, as sand boundaries do not constrain movement in the initial 48 h after release.
Evaluating survival of juveniles in pilot-scale releases
All pilot scale releases of cultured lobsters were combined with tagging of control, wild juveniles and survival was measured relative to those wild juveniles. This was because the object of releasing juveniles was not to eliminate predation, only to reduce it to the same level as experienced by wild juveniles. Pilot scale releases were conducted at 4 sites that spanned 2 bioregions.
A total of 2244 lobsters were released and all were individually marked with antennal tags. These tags allowed divers to identify the juveniles without capturing them. The survival of juveniles after release was monitored by a series of intensive diver surveys on the release reef and also neighbouring areas. Survival was estimated from this resighting data using modern survival estimation models (Cormack-Jolly-Seber and multistate derivatives). We used these models in an attempt to separate movement from survival, although it is clear that our estimates of survival remained biased lower by movement. That is, our estimates of “mortality” include some individuals that left the site by walking, rather than dying.
Initial releases took place on isolated patch reefs with the aim of retaining lobsters within an area that could be readily searched by divers. This approach was later changed to release on contiguous reef when it was apparent that a sand edge was not a barrier to lobsters movement during their initial ‘flight’ response. Models that included movement parameters (multistate models) and acoustic tracking revealed that on-grown lobsters tend to move further than wild-caught lobsters during the initial ‘flight’ response.
At 3 of the 4 sites, there was no detectable difference between survival of cultured and wild-caught lobsters, suggesting that any artefacts of the ongrowing and release processes had no effect at these sites. This result was encouraging for enhancement operations as it implied that the risk of mortality for released juveniles rapidly became equivalent to that of a wild juvenile.
At the 4th site (Adventure Bay), apparent survival was lower for on-grown lobsters in the first 24 h post release. Video-referenced tethering trials showed that predation pressure at that site was no higher than at other sites. However, this site differed from the others in that it was the smallest area of reef, with proportionally more ‘edge’ due to it’s long and narrow shape. The reef was surrounded by large expanses of sand with little neighbouring reef. The observed difference in apparent survival was likely to be caused by these site differences. As naïve lobsters move further than wild-caught lobsters on release, a larger number will move off the reef and onto sand. As there was little other reef surrounding the release reef, mortality amongst lobsters that leave this reef was apparently high.
At 3 of the 4 sites, apparent survival was lower for the first 24 h post release than for the remainder of the trials. Evidence from diver and camera observations following release, maximum likely predation estimates from camera-referenced tethering trials, and an experiment using seafloor cages in combination with acoustic tags suggest that this lower “survival” was due to movement away from the survey site rather than high predation when released.
In summary, survival of released juveniles appears equivalent to that of wild lobsters of an equivalent size after 48 h post release. Estimates of survival of cultured juveniles were sometimes lower than that of wild controls in the first 48 h post release, although these occasions appeared to be biased to some extent by movement. That is, released juveniles appear to have disappeared from surveys by walking rather than from predation.
KEYWORDS: rock lobster enhancement, Jasus edwardsii, survival estimation, mark-recapture.
Novel options for enhancing catch in the Tasmanian rock lobster fishery have been proposed,
including the harvest and ongrowing of puerulus, and the translocation of under-size lobsters
from slow growth to fast-growth regions. Both of these proposals involve translocating
lobsters between locations, which has led to concerns about the risk of disease transfer
between regions. The issue of disease transfer is even broader than these novel management
measures because rock lobsters are extensively moved around the State through normal
fishing operations. In response to these concerns, a health survey was initiated to determine
what diseases are present in Tasmanian rock lobster populations, and the distribution of those
diseases.
The survey assessed the health of 374 juvenile southern rock lobsters, and compared the
health of the 234 wild animals from six of the seven recognised bioregions around Tasmania
and the 140 animals from four cultured populations that had been ongrown since collection as
pueruli. (The seventh Tasmanian bioregion contains few animals and was not included in the
sampling.) The cultured groups comprised two populations raised in consecutive years from
one on-shore flow through facility, and two populations raised in sea-cages. The number of
ongrown samples was less than anticipated due to slower than expected development of the
ongrowing sector, but represented samples from all the available populations.
Examinations consisted of gross and histological examination of a range of tissues from all
animals, plus culture and haematology counts from selected animals. No clinical,
bacteriological or histopathological evidence of significant infectious diseases was detected in
any groups, though mild lesions associated with ubiquitous organisms and occasional
individual animals with more marked pathology were seen.
An assessment of the risk posed by release of these ongrown animals into wild areas was
carried out, and was completed with no potential hazards identified from the survey. A
contraction of further planned releases from ongrown juveniles prevented development of a
tailored health testing protocol for this sector. Nevertheless a precautionary approach to future
translocations, and a proactive approach to continued general health surveillance for the wild
as well as ongrowing sector is recommended.
Findings were further analysed to increase understanding of disease processes and reactions
in this species, to aid diagnosis and health testing in the future, to compare the health
implications of the two culture systems, and to allow comparisons with populations sampled
in the future. A summary of major findings from these analyses is as follows:
• The only conditions consistently more marked in ongrown than wild stock were those of
gill fouling and minor integument erosion, which were probably related. There were more
differences between the batches within each type of culture system than between the
systems, with length of culture period (and its corollary, size) appearing to be the major
determinant of the severity.
• The level of bacterial carriage was low in all groups, despite other evidence of capture and
transport stress. The aim for bacterial culture was to sample at least 10% of animals,
including any ill animals. The actual number of haemolymph cultured was 87 (23%), with
very few ill animals detected. Although eight animals showed carriage of low levels of
bacteria, bacteria were not isolated in sufficient number from any animal to indicate active
infection prior to sampling, and there was no histological evidence of bacterial disease in
these animals. The bacteria identified from haemolymph cultures were low numbers of
Vibrio splendidus I on seven occasions, from two ongrown animals (one on-shore, one
sea-caged), and five wild animals from two growing areas, and one isolate of Vibrio
navarrensis. While V. splendidus I has been implicated as a pathogen from some species it
is more commonly seen as an opportunistic invader, V. navarrensis has not been reported
as a pathogen in aquatic animals. Both are regarded as opportunistic infections of animals
stressed by the collection process.
• Histological examination only occasionally showed bacteria within the tissues of other
animals apart from surface fouling. Bacteria were detected in one wild animal with severe
and apparently long-standing hepatopancreas damage resulting in almost total destruction
of this organ. Similar cases have been reported elsewhere in this and other decapod
species, generally as sporadic cases or related to inadequate manufactured diets.
• Several external parasites were associated with a mild host reaction though the overall
effect on lobster health appeared slight. Parasites were almost entirely restricted to
ectoparasites of the gill and (of less significance) the skin. These included protozoan
fouling agents, turbellarians, goose barnacles, and other unidentified small crustacea.
Turbellarians appear not to have been previously reported from lobsters, though they are
common ectoparasites of molluscs.
As well as the recognisable mild pathology associated with these pathogens, a number of
tissue changes of uncertain origin were seen. One change, a zonal degeneration of the
antennal glands, was regarded as of sufficient severity to be of concern with regard to
long-term health of these individuals, though the number of affected animals was low and
virtually all were in wild caught lobsters. The appearance generally was that of a recent
change, though it was not established whether any of these lesions were likely to have
been present prior to capture. Electron microscopic examination, undertaken as a
precautionary measure only, excluded viruses as a cause of this condition but did not
establish the nature of the cell changes. This change has been reported previously in
Australia in one tropical lobster, and similar but not identical changes have occasionally
described from other species. Though the cause or causes have not been identified for any
of these, they do not appear to be infectious.
• Acute muscle damage was very common (almost 100% in one wild group), and was
suspected to be an indication of capture or post-collection stress. The most severely
affected group also showed a number of animals with mild turgid lobster syndrome.
• The reactions and cell changes associated with this and other pathology were examined
for possible correlations which may warrant follow up under more controlled conditions,
or by comparison of more sample sets over time. The detailed record of findings from this
survey will facilitate subsequent examinations.
OUTCOMES ACHIEVED
The project provided confirmation that:
• the overall disease levels in juvenile southern rock lobsters Jasus edwardsii in Tasmania
are low;
• that there was no evidence of major diseases, and;
• that juvenile rock lobsters could be ongrown under conditions which did not enhance
diseases in a manner posing a risk to wild populations, if released.
As well as providing background data on health status of Tasmania’s rock lobsters, this
project provided knowledge on interpretation of pathological changes and tissue variations in
this species.
The 2000/2001 assessment investigated a number of issues relating to the rock lobster
assessment model. These were:
1. correction of systematic errors in the catch and effort database associated with
translations between catch weight estimation errors;
2. incorporation of new recreational catch estimates and the ability to vary this
annually;
3. changes in the fleet dynamics component of the model;
4. adjustments to the size at onset of maturity in each area; and
5. evaluation of the magnitude of lobster movement between areas.
The effects of these changes are documented in this report.
No trigger points were reached in this year’s assessment. Catch rates (commercial and
research), legal-sized biomass and egg production were all above the reference years.
Compared to the 1999/2000 fishing season, indicators were either stable (catch rates) or
improving (legal-sized biomass). Egg production was improving in northern regions
except in area 4, which had a decline. This decline follows the rapid increase in egg
production estimated in 1998/1999 and 1999/2000 fishing seasons as a large
recruitment pulse occurred in the fishery in this region.
Puerulus settlement indices in eastern Tasmania continue to provide a strong correlation
with 5 year lagged catch rates from the fishery for the East Coast. If this correlation is
maintained, the puerulus index indicates that catch rates on the East Coast will decline
and remain relatively low over the next 5 years. Although the period of puerulus
settlement monitoring has not been sufficient to determine a relationship between
puerulus index and lagged catch rates in north-western Tasmania, a relatively large
puerulus settlement occurred in 1999 which may result in improved catch in this region
over forthcoming years. The ability of the fleet to move to different locations to
improve or maintain catch rates (fleet dynamics) is therefore likely to be important over
the next 5 years.
Harvest strategies based on the current TACC of 1500 tonnes and increases to 1523,
1550 and 1576 tonnes were evaluated up to 2004. In general TACC’s of up to 1550
tonnes show relatively stable projections of biomass to the year 2004, although there is
considerable uncertainty around the 2004 estimates. Regionally, predicted biomass
improvements in the east are expected to be offset by declines in the west. Statewide
egg production predictions increased under all TACC scenarios. Egg production in
northern regions is currently less than the target of 25% of an unharvested population.
Expected future trends in these regions were mixed with improvements expected in
north eastern regions while minor declines are expected in north western regions. None
of the TACC scenarios indicate that egg production in northern regions will reach the
25% target by 2004.
Future projections of regional biomass and egg production estimates are dependent on
the movement of the fishing fleet between regions. Evaluation of a number of fleet
dynamic models using differing years of data suggests that there has been a change in
fishing patterns since the introduction of the ITQ management system in March 1998.
However, as only two years of data are available for a purely post-ITQ fleet dynamics
model, future projections are based on a 10 year data set from 1990 to 2000. As the
majority of data is from the pre-ITQ period, caution is required when interpreting
regional estimates.
The number of recreational licences has continued to increase although estimates of
catch have not increased at the same rate. Nevertheless, the catch is moving towards the
10% of commercial catch trigger point and monitoring needs to be continued.
Projects focusing on socio-economics of the fishery, ecosystem interactions and
aquaculture are underway and details of these projects are incorporated in the report.
Ecosystem projects are addressing the increased prevalence of the barren forming
urchin Centrostephanus rodgersii, the impact of the major loss of the giant kelp
Macrocystis pyifera and the biology and ecology of a main lobster predator Octopus
maorum.
Aquaculture is dependent on obtaining post-larval lobsters from the wild. To
compensate for their removal a percentage of these lobsters have to be returned to the
wild after one year in culture, Research projects are addressing issues such as mortality
rates, growth and disease to ensure minimal impact on the resource and no negative
impact on the commercial catch.
