Are hatchery‐reared abalone naïve of predators? Comparing the behaviours of wild and hatchery‐reared northern abalone,Haliotis kamtschatkana (Jonas, 1845)

Abalone populations have declined worldwide, generating interest in enhancement using hatchery‐reared individuals. In many cases, such restoration efforts have met with limited success due to high predator‐induced mortality rates. Furthermore, the mortality rates of outplanted hatchery abalone are often considerably higher than for wild individuals. This study uses northern abalone (Haliotis kamtschatkana) as a case study to determine whether hatchery‐reared abalone behave differently than their wild counterparts. In the field, outplanted hatchery‐reared abalone were significantly less responsive than wild abalone, in terms of number of abalone responding and intensity of response, to nearby movement and to physical contact with an inert probe. Also, when encountering a cue to which all abalone responded (a seastar predator), hatchery‐reared individuals remained subdued. Anti‐predator behavioural deficits in hatchery‐reared abalone were more pronounced in 4‐year‐old individuals than in 1‐year‐old individuals, suggesting an influence of either age or amount of time spent in the hatchery environment. These behavioural differences are expected to increase the vulnerability of hatchery‐reared abalone to predators, and are likely a major cause of their elevated predator‐induced mortality when outplanted.     

The predation of trumpet shell, Charonia sp., on eight different marine invertebrate species

In this study, predation of the trumpet shell, Charonia sp., on different invertebrate prey species, e.g. starfish, Asterina pectinifera and Asterias amurensis, abalone Haliotis discus hannai, clam Anadara broughtonii and Tapes phillipiarum, and sea urchin Hemicentrotus pulcherrimus and Anthocidaris crassispina, was measured in a laboratory experiment. Each prey species was placed in a tank with a trumpet shell; prey species were not combined. Each combination of prey and trumpet shell was replicated three times. Trumpet shells did not prey on economically important shellfishes, including Anadara broughtonii, Tapes phillipiarum and Haliotis discus hannai. Sea stars were most preferred by the trumpet shell. The following preference gradient from most to least preferred was found: sea stars > sea cucumber > sea urchin. In selected situations, trumpet shells may be a means of biological control of predators of economically important shellfish.     

Feasibility of Offshore Co‐culture of Abalone,Haliotis discus hannai Ino,and Sea Cucumber,Apostichopus japonicus,in a Temperate Zone

Feasibility of offshore co‐culture of abalone and sea cucumber was investigated in Northern China. Survival and growth of abalone, Haliotis discus hannai Ino, and sea cucumber, Apostichopus japonicus, co‐cultured in abalone cages from suspended longlines, in the offshore area, were examined. Abalone and sea cucumbers were co‐cultured at density ratios of both 3:1 and 6:1 for 1 yr. Abalone were fed with fresh kelp and no additional feed was given to sea cucumbers. Survival of abalone and sea cucumber was 100% for all treatments. Abalone and sea cucumber grew well; the body weight (BW) of abalone and sea cucumber was nearly doubled and had reached a commercial size. There were no significant differences in the growth rates for both abalone and sea cucumber between the two density treatments. The specific growth rate of BW of abalone (SGRbw) was highest in June, with a value of 0.536%/d. Growth rate of sea cucumber (SGRsc) was highest in December, reached 1.84%/d, with an annual average SGRsc of 0.182%/d. Results suggested that the offshore co‐culture of abalone and sea cucumber was feasible offshore. The co‐culture of abalone with sea cucumbers may provide an additional valuable crop without additional financial input.     

Morphological conditioning of a hatchery-raised invertebrate,Callinectes sapidus,to improve field survivorship after release

For recruitment-limited, severely depleted fishery stocks, stock enhancement may become an important technique in the return of population sizes to sustainable levels. Aquaculture-reared individuals, however, may face some disadvantages upon release into the wild due to differences between natural conditions and the hatchery. The goal of this study was to test whether field survivorship of hatchery-raised blue crabs, Callinectes sapidus, could be improved by simple conditioning steps, taking advantage of phenotypic plasticity in certain traits. This species is currently the focus of a preliminary stock enhancement program in the Chesapeake Bay. Results indicate that unconditioned hatchery crabs had lower survivorship than wild crabs in the field and differed in carapace color and lateral spine length. Both traits were plastic. Carapace color was changeable within 1–2 days, without a molt, upon the exposure of crabs to new substrates. However, colors within the range produced in this study did not significantly affect survivorship in a field or a laboratory experiment. Change in spine length required exposure to predators for 1–4 weeks. Exposure to fish predators resulted in increased spine length, though exposure to adult blue crabs had no significant effect. Crabs with lengthened spines had significantly higher survivorship in both laboratory and field experiments, suggesting that this feature may be one on which to focus large-scale conditioning efforts. Results of this study suggest a level of phenotypic plasticity that may contribute to the blue crab's ability to take advantage of multiple estuarine habitat types. On a more applied level, results of this study suggest that at least some deficiencies in hatchery-raised organisms can be alleviated and would likely lead to improved success and efficiency of stock enhancement efforts. Similar studies on other hatchery-raised invertebrates and finfishes may also lead to improvements in their enhancement programs.     

Factors affecting the recapture of undersize western rock lobster Panulirus cygnus George returned by fishermen to the sea

The rock lobster fishery of Western Australia is one of the largest of its kind; its average catch in the years 1974/75 to 1981/82 was almost 10000 tonnes. The fishery has been stable for many years, largely by virtue of licence limitation and other management measures. Among the regulatory measures is a requirement that all traps used in the fishery must be furnished with escape gaps and another requires fishermen to return to the sea all undersize lobsters that enter the traps, but fail to escape and consequently are brought on board the fishing boat when the trap is lifted.Despite the presence of the escape paps, considerable numbers of undersize lobsters are brought aboard; the number is estimated to be some 16 to 20 million in each season. Moreover, it has been estimated that about a quarter of these retained undersize lobsters remain on board for 10 min or more, and some have been observed to remain on board for more than two hours.Studies were therefore undertaken to ascertain whether this cipture-and-release experience was in fact causative of mortality. Laboratory experiments on animals exposed in direct sunlight resulted in an expected time for 50% mortality of 99, 158 and 233 min with increasing temperature compared with a time of 387 min for animals exposed under shade.Behavioural observations showed that as exposure time increased, returned animals exhibited a decreasing rate of descent through the water column, a decrease in the percentage of active animals and increased loss from predators. In addition, in ten laboratory experiments on octopus predation, octopus predated or injured animals exposed for 15 or 30 min, despite a recovery period of 3.5–5.5 h, but not on unexposed animals.Four tagging operations with over 7000 undersize animals resulted in a significant decrease in recapture rates by commercial fishermen with increasing exposure times. Damage (number of appendages lost) incurred by the rock lobsters and displacement beyond the home range were also generally found to reduce the recapture rates significantly. The combination of all these factors resulted in an estimated reduction in recapture rate of 14.6% in the 1978/79 fishing season and after taking into account natural mortality, this would have resulted in a loss of $A6.4 million to the fishery.     

Survival and growth of hatchery-reared individuals of the European lobster, Homarus gammarus (L.), in field-based nursery cages on the Irish west coat

At present, one of two strategies is employed by fisheries managers for enhancing wild stocks of homarid lobsters using hatchery-reared individuals. The first is repeated releases of large numbers (>5000 at a time) of postlarvae (stage IV and V; carapace length [CL]=5–7 mm) to selected bottom locations. This option exists primarily because these programs lack space, time, and/or the finances to rear animals to larger sizes that would most likely have initially higher survival rates. The second is to rear animals in the laboratory for 5–8 months to stage XII+ (CL=12–16 mm) and then release small numbers (<1000) of these relatively large juveniles. To date there has been no attempt to release large numbers of relatively large juveniles because the costs are too prohibitive.

We have developed a low-cost, low-maintenance, field-based nursery caging system for rearing cultured lobsters, Homarus gammarus (L). Individuals (780 and ranging in CL from 5.2 to 7.2 mm) were reared in pre-fouled and unfouled containers (360 cm³) fabricated from an extruded plastic netting (3.2 mm aperture) and in pre-fouled plastic petri dishes (200 cm³) that were deployed in five near-bottom cages for 10 months (September 2000 to June 2001) at two subtidal sites located in a shallow, relatively exposed embayment on the west coast of Ireland. Animals apparently were able to survive and grow by suspension feeding on the plankton and/or foraging on the fouling community that settled on and within individual containers. Mean recovery rate (±95% CI) was independent of a priori fouling treatments, but was site-specific (42.1±7.9% and 27.8±13.7%; n=5). These rates are minimal estimates of survival because we found that at least 20% of the animals were capable of escaping from the mesh containers. Mean recovery in petri dishes that prohibited emigration was 53.3±37.02% at one site and 75.0±23.1% (n=5) at the other. These recovery rates compare favorably with survival rates of fed conspecifics held in the laboratory over the same time (54/81=66.7%). At the end of the experiment, animals in field cages had mean CLs that were significantly smaller than the fed controls. Because of costs incurred with maintaining small lobsters under laboratory conditions, results of this short-term, manipulative field experiment indicate that field-based nurseries represent an economically viable, third option for managers of lobster stock enhancement programs.     

Do predators,handling stress or field acclimation periods influence the survivorship of hatchery‐reared abalone Haliotis kamtschatkana outplanted into natural habitats?

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Interactions between predatory sea stars (Asterias amurensis and Distolasterias nipon) and Japanese scallops (Mizuhopecten yessoensis) and implications for scallop seeding in mariculture

Sea stars are a key group of species in benthic marine ecosystems and represent the primary cause of mortality for cultured scallops. In the mariculture grounds of Japanese scallops (Mizuhopecten yessoensis) in north‐eastern Japan, two sea star species, Asterias amurensis (AA) and Distolasterias nipon (DN), are serious predators. However, the predatory impact of these sea stars on scallops remains unquantified, with limited information being available on the biological characteristics of DN. We compared the predatory impact of both sea star species by evaluating their predatory behaviour (i.e. probability of predation and number of captured scallops) on scallops in laboratory experiments. Both sea star species preferred smaller scallops over large ones, with the probability of predation and the number of scallops being preyed on increasing with increasing water temperature. However, DN had a greater predation impact than AA. For instance, the probability of predation by DN was higher, with more scallops being consumed. In particular, compared to AA, DN continuously captured small scallops and fed on larger scallops. Furthermore, the predatory impact of both sea star species (particularly DN) on small scallops peaked at high temperatures. In conclusion, our results present information that could help improve the survival rate of seeded scallops in mariculture systems.     

Comparison of nutrients release among some maricultured animals

Integrated mariculture is a feasible method to maintain sustainable and high productivity of aquaculture. The choice of cultured animals and biofilters in the integrated system has to be made on the basis of their nutrient release rates and the clearance rate of each component of the system. We are examining the nutrient release rates among fish (mangrove snapper, Lutjanus russeli, and sea perch, Abudefduf septemfasciatus), abalone (Haliotis diversicolor), scallops (Chlamys noblis), and green mussels (Perna viridis) in the laboratory. Fish feed is the major sources of inorganic nutrient input in fish farms. The orthophosphate and ammonia release rates of minced trash fish (1593 μg P g⁻¹ day⁻¹ and 150 μg N g⁻¹ day⁻¹) were respectively 6–12 times and 4–88 times higher than those of cultivated fish. Mangrove snapper had the overall highest nutrient release rate, followed by sea perch, abalone, scallops, and mussels for nitrite and nitrate; and followed by abalone, sea perch, mussels, and scallops for orthophosphate and ammonium. Among mollusks, abalone had the highest orthophosphate (162 μg P g⁻¹ day⁻¹), nitrate (1.4 μg N g⁻¹ day⁻¹), nitrite (1.6 μg N g⁻¹ day⁻¹) and ammonium (25.0 μg N g⁻¹ day⁻¹) release rates per gram wet weight per day. Abalone released large amounts of orthophosphate, nitrite and nitrate in the experiment. Scallops and green mussels had low nutrient release rates.     

A comparison of claw morphology and dominance between wild andcultivated male European lobster

Claw size and dominance in cultivated versus wild European lobsters Homarus gammarus were compared. Normally, lobsters develop a short, high and wide crusher and a slender scissor claw. In culture, both claws often develop into scissor claws. With growth, cultivated males developed one significantly elongated scissor claw (major claw), and one normal scissor claw, compared to wild males (minor claw). The differences increased with size. The wild males had higher claw index than cultured ones, due to the crusher claw. Wild lobsters with higher claw index were dominant. Cultivated males with claw indices at least 200 mm² higher than the opponent, won. Only scissor claws were broken in the encounters. Even if cultivated lobsters in time develop claws equal to wild lobsters, they might still be less robust. In the light of these findings, we suggest that lobsters cultivated for restocking purposes should be given access to an appropriate substrate allowing them to develop one claw into a crusher during the early benthic stage.     

Spatial abundance patterns and recruitment of a virus‐affected commercial mollusc fishery

Infectious pathogens figure prominently among those factors threatening marine wildlife. Mass mortality events caused by pathogens can fundamentally alter the structure of wild fish stocks and depress recruitment rates and yield. In the most severe instances, this can precipitate stock collapses resulting in dramatic economic losses to once valuable commercial fisheries. An outbreak of a herpes‐like virus among commercially fished abalone populations in the south‐west fishery of Victoria, Australia, during 2006–2007, has been associated with high mortality rates among all cohorts. Long‐term records from fishery‐independent surveys of blacklip abalone Haliotis rubra (Leach) enabled abundance from pre‐ and post‐viral periods to be analysed to estimate stock density and biomass. The spatial distribution of abundance in relation to physical habitat variables derived from high‐resolution bathymetric LiDAR data was investigated. Significant differences were observed in both measures between pre‐ and post‐viral periods. Although there was some limited evidence of gradual stock improvement in recent years, disease‐affected reefs have remained below productivity rates prior to the disease outbreak suggesting a reduction in larval availability or settlement success. This was corroborated by trends in sublegal sized blacklip abalone abundance that has yet to show substantial recovery post‐disease. Abundance data were modelled as a function of habitat variables using a generalised additive model (GAM) and indicated that high abundance was associated with complex reef structures of coastal waters (<15 m). This study highlights the importance of long‐term surveys to understand abalone recovery following mass mortality and the links between stock abundance and seafloor variability.     

A rapid onset, post-capture muscle necrosis in the Norway lobster, Nephrops norvegicus (L.) from the West coast of Scotland

A post-capture, abdominal muscle necrosis of rapid onset has been identified in Norway lobsters, Nephrops norvegicus (L.), captured off the West coast of Scotland. Economic losses, as a result of the mortality of these animals in transport, were encountered by Scottish wholesalers during the summer and autumn of 1999. Affected animals show a characteristic whitening of individual muscle fibres and fibre bundles of the abdomen within hours of capture, with a progression towards complete opacity of the abdominal musculature within a number of days. The pathology causes a loss of the normal function of the abdomen; thus, preventing the normal 'tail flip' swimming. Electron microscopy failed to reveal any obvious causative agent but showed that affected tissue displayed a progressive disruption of sarcomere organization, loss of Z-line material, condensation of myofibrils and infiltration of necrotic regions by granulocytes. SDS–PAGE of affected muscle tissue showed that there was a great reduction of most of the major contractile proteins. The condition most closely resembles idiopathic or spontaneous muscle necrosis, a pathology previously reported from both wild and cultured crustaceans. Damage to the integument in conjunction with exposure to various stressors during and immediately after capture is the most likely cause of the pathology. The rapid onset of the pathology has implications for the post-capture handling procedure for N. norvegicus and their subsequent vivier transport to market. It may also be partially responsible for the high mortality rate of undersized N. norvegicus returned to the sea after capture and aerial emersion.     

Acute toxicity of emamectin benzoate (SLICE™) in fish feed to American lobster, Homarus americanus

SLICE? (active ingredient 0.2% emamectin benzoate (EMB)), a feed premix developed by Schering‐Plough Animal Health for the control of sea lice on cultured salmonids, is registered for use in several countries and is being prescribed on an emergency basis in Canada and the United States. The concentration of EMB in feed administered to farmed salmon ranges from 1 to 25 μg g^?1. To determine the acute toxicity of the compound to juvenile and adult American lobster (Homarus americanus), commercial salmon feed was coated with SLICE? at a range of concentrations and provided to the animals for 7 d in the laboratory. The LC₅₀ is estimated to be 644 μg g^?1 (95% CI=428, 1275) for adult lobsters and >589 μg g^?1 for stage V and VI juvenile lobsters. The consumption of medicated pellets by adult lobsters decreased significantly with increasing concentration of EMB. Adult lobsters that died during the study had a significantly greater concentration of emamectin B1a in their muscle tissue than those that survived. These results support the conclusion that salmon feed medicated with EMB at the concentrations used by the aquaculture industry is unlikely to pose an acute lethal threat to adult and small juvenile American lobsters.     

Rock crab predation of juvenile sea scallops: the functional response and its implications for bottom culture

The functional response describes how consumption rate of individual predators changes as prey density changes, and can have important implications for the bottom culture of scallops. We examined (i) the functional response of rock crabs (Cancer irroratus) preying on juvenile sea scallops (Placopecten magellanicus); (ii) the effect of substrate type and scallop size on the functional response; and (iii) the underlying behavioural mechanisms of observed functional responses. Specifically, we quantified predation rate and behaviours, such as the proportion of time spent searching for prey, encounter rate between predators and prey and the outcomes of encounters, when individual rock crabs were offered a range of scallop density (2–50 or 11–111 scallops m⁻²) and two size classes of scallops (∼ ∼25 and ∼ ∼35 mm shell height) on two different substrate types (“glass-bottom” and “granule”). We found that crab predation rate on small juvenile scallops increased at a decelerating rate with prey density to a plateau at high prey density on both substrates, indicating a hyperbolic (type II) functional response. Crab predation rate on large juvenile scallops was independent of prey density (i.e., no functional response evident), suggesting that crabs were at their satiation level. Prey density did not influence any behaviour except encounter rate on small juvenile scallops, which increased as prey density increased. Substrate type influenced crab predation: maximum predation rate of crabs on small juvenile scallops and encounter rate with either size of juvenile scallops was lower on granule than on glass-bottom. Our results in the laboratory suggest that crabs could potentially be swamped if scallops are seeded at a high density in the field. However, many factors in the field may influence the functional response. For example, the presence of multiple prey types may lead to sigmoid functional responses, while the presence of many crab individuals may lead to aggregation of crabs in areas of high prey density.     

野生和养殖三疣梭子蟹消化酶及SOD酶活性的比较分析

为揭示三疣梭子蟹(Portunus trituberculatus)不同生长阶段的消化酶和超氧化物岐化酶(SOD)活性的变化规律,及其与生长环境之间的关系,以野生和养殖三疣梭子蟹的幼蟹、雌性成蟹及抱卵雌蟹为研究对象,分别测定比较了其肝胰腺中的胃蛋白酶、脂肪酶、淀粉酶及肌肉中的SOD活性,结果表明:(1)野生和养殖幼蟹的淀粉酶活性分别为(1.57±0.09)U.mg-1和(2.61±0.01)U.mg-1,显著高于成蟹和抱卵蟹(P<0.05);野生和养殖成蟹的胃蛋白酶活性分别为(5.83±0.45)U.mg-1和(2.77±0.10)U.mg-1,显著高于幼蟹和抱卵蟹(P<0.05),是幼蟹和抱卵蟹的2～3倍;脂肪酶活性以养殖抱卵蟹最高,野生成蟹次之;消化酶活性变化与蟹的生长阶段及食性转变相关。(2)幼蟹、成蟹和抱卵蟹的SOD酶均表现为野生蟹显著高于养殖蟹(P<0.05);野生成蟹的脂肪酶和胃蛋白酶活性亦显著高于养殖成蟹,是养殖成蟹的2.5倍以上。因此,养殖蟹的机体健康水平、免疫保护和抗应激能力不及野生蟹,尤以幼蟹阶段SOD酶活性最低,抗逆境力最差。     

A method for inducing muscle relaxation in the abalone, Haliotis iris

Four chemical and two non-chemical methods for induction of relaxation in the abalone, Haliotis iris, were tested for prospective use in pearl seeding. Requirements were for rapid onset of relaxation, full extension and softening of the foot and epipodium muscle for at least 10 min, and recovery with minimal stress and no mortality. Nembutal at 1 ml/l was most successful, producing relaxed and soft muscle with good accessibility to operation sites, and no mortality. Benzocaine and MS-222 made animals release from container walls within 30–60 min, but the animal's muscle was hard and contracted. Propylene phenoxytol caused muscle contraction and mortality at 2.5 ml/l. The effects of the chemical relaxants were similar in warm (21–22.5°C) and cool (15–16°C) water. Elevation of the water temperature from 18°C to 23°C (without chemicals) caused some softening of the muscle, but was much less effective than Nembutal. Air exposure for up to 4 h was ineffective. This work provides a simple method to relax live abalone for pearl nucleation or other manipulations.     

Community and trophic structures of abalone <Emphasis Type="Italic">Haliotis diversicolor</Emphasis> habitat in Sagami Bay,Japan

Abstract:   The community and trophic structures of the subtidal habitat of the abalone Haliotis diversicolor were examined in Nagai, Sagami Bay, Japan. Conventional community indices showed no significant differences among three sampling stations. The overall continuum of stable isotope ratios was structured into three different trophic linkages: (i) brown algae-dependent benthic food chain; (ii) red algae-dependent benthic food chain; and (iii) planktonic food chain. Brown algae and red algae likely play different roles with respect to carbon sources in the habitat. Conventional fractionation values indicated that the abalone H. diversicolor (δ¹³C = −12.4 ± 1.0‰, δ¹⁵N = 9.3 ± 0.5‰) feeds on the lamina of Undaria pinnatifida during juvenile and adult stages (8.0–65.6 mm shell length). Stable isotope signatures suggested that the juveniles of other abalone species as well as some amphipods and a sea cucumber Holothuria decorata are competitors of H. diversicolor , whereas some Muricidae gastropods such as Thais bronni and Ergalatax contractus are predators. The isotopic differences among macroalgal species and the subsequent transfer to consumers indicate that stable isotopic analysis is an effective means of studying food webs in an open rocky shore community with little influence from external primary production such as terrestrial vegetation.     

Experimental host range and histopathology of white spot syndrome virus (WSSV) infection in shrimp, prawns, crabs and lobsters from India

Experimental studies were conducted by injecting or feeding white spot syndrome virus (WSSV) derived from infected shrimp, Penaeus monodon (Fabricius), collected from the south-east coast of India, to five species of shrimp, two species of freshwater prawns, four species of crabs and three species of lobsters. All species examined were susceptible to the virus. Experimental infections in the shrimp had the same clinical symptoms and histopathological characteristics as in naturally infected P. monodon . A cumulative mortality of 100% was observed within 5–7 days in shrimp injected with WSSV and 7–9 days in shrimp fed with infected tissue. Two species of mud crab, Scylla sp., survived the infection for 30 days without any clinical symptoms. All three species of lobsters, Panulirus sp., and the freshwater prawn, Macrobrachium rosenbergii (De Man), survived the infection for 70 days without clinical symptoms. However, bioassay and histology using healthy P. monodon revealed that crabs, prawns and lobsters may act as asymptomatic carriers/reservoir hosts of WSSV. This is the first report to suggest the carrier/reservoir capacity of these hosts through histological and bioassay evidences. Ultrastructural details of the virus in experimentally infected shrimp, P. vannamei , (Boone), were also studied.     

Survey estimates of fishable biomass following a mass mortality in an Australian molluscan fishery

Mass mortality events are relatively uncommon in commercially fished populations, but when they occur, they reduce production and degrade ecosystems. Observing and documenting mass mortalities is simpler than quantifying the impact on stocks, monitoring or predicting recovery, and re-establishing commercial fishing. Direct survey measures of abundance, distribution and harvestable biomass provide the most tenable approach to informing decisions about future harvests in cases where stock collapses have occurred because conventional methods have been disrupted and are less applicable. Abalone viral ganglioneuritis (AVG) has resulted in high levels of mortality across all length classes of blacklip abalone, Haliotis rubra Leach, off western Victoria, Australia, since May 2006. Commercial catches in this previously valuable fishery were reduced substantially. This paper describes the integration of research surveys with commercial fishermen's knowledge to estimate the biomass of abalone on AVG-impacted reefs. Experienced commercial abalone divers provided credible information on the precise locations of historical fishing grounds within which fishery-independent surveys were undertaken. Abalone density estimates remained low relative to pre-AVG levels, and total biomass estimates were similar to historical annual catch levels, indicating that the abalone populations have yet to adequately recover. Survey biomass estimates were incorporated into harvest decision tables and used with prior accumulated knowledge of the populations to determine a conservative harvest strategy for the fishery.     

Status and habitat associations of the threatened northern abalone: importance of kelp and coralline algae

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