Stress and mortality in the supply chain of live scallops Pecten maximus L., from scuba diver to market

Here, we report results from a project where the aim was to study stress and mortality in the supply chain from harvest to market for live scallops Pecten maximus L., hand‐picked by scuba divers. With experiments conducted both during the warm (September) and cold (April) seasons, emphasis was put on how mechanical influence, stacking height, post‐harvest water storage and dry transport affected scallop fitness. When scallops were exposed to mild‐ or hard mechanical shocks (dropped three times from 50 or 150 cm), it was found that hard mechanical shock caused up to 90% mortality during subsequent water storage. Results from the experiments where scallops were stored at different stacking heights (15, 30 and 50 cm) in water showed that both the duration of storage and the stacking height had a significant effect on mortality. Higher stacking heights also affected survival in subsequent transport. For long‐term storage (>7 days), it is recommended to limit the stacking height of scallops stored in tanks to reduce risk of mortality. Respiration experiments showed an average oxygen consumption of 0.10 and 0.24 mg O₂ min^?1 kg^?1 f.w. in the cold and warm season respectively. Water supply during storage of scallops should be adjusted to water temperature and biomass. Registration of mortality and analysis of the Adenylic Energy Charge of scallops followed through the production cycle from harvest to market indicate that it is the sum of stressors that are determinable for final survival.     

Survival and growth of hatchery-produced postlarvae and spat of the Caribbean scallops Argopecten nucleus and Nodipecten nodosus

A study was made of the growth and survival of postlarvae and spat of Argopecten nucleus and Nodipecten nodosus produced in the laboratory and exposed to different conditions of settlement and culture. An evaluation was made of the different types of collection substrates (onion-bags, artificial-grass, fibreglass-plates), two types of settlement inducers (epinephrine, low temperature), and two culture environments (sea, laboratory). The results showed that larger numbers of postlarvae were obtained in artificial-grass collectors than on fibreglass-plates or in the onion-bags. The growth of the A. nucleus postlarvae was not affected by the collector type, while that of N. nodosus was higher on fibreglass-plates, and lesser in the onion-bags. Both thermal and chemical stimulation of the competent larvae resulted in recovery of a greater percentage of postlarvae. The growth of postlarvae of A. nucleus was better in groups exposed to the two methods of settlement induction, while those of N. nodosus remained unaffected by this treatment. The survival of the postlarvae and spat was greater in the laboratory than at sea except in the case of A. nucleus postlarvae attached to collectors, whose survival was similar in both environments. The growth of postlarvae and spat was greater in the sea than in the laboratory.     

Efficacy of Netminder® silicone release coating for biofouling reduction in bay scallop grow‐out and comparative effects on scallop survival,growth and reproduction

Netminder^®, a water‐based silicone barrier release coating, was highly effective in reducing biofouling of lantern nets during grow‐out/overwintering of bay scallops, Argopecten irradians irradians, in a large‐scale restoration programme in New York, USA. Compared with untreated nets, scallops held in Netminder^®‐coated nets experienced reduced survival after 8 months, probably due to higher loads of epibionts on their shells. However, this was countered by higher reproductive and overall condition of scallops in treated vs. untreated nets; there were no consistent differences in shell growth in different net treatments. Although further testing is recommended under a wider range of conditions, we conclude that for the purposes of our scallop restoration work, coating nets with Netminder^® would eliminate the need for a gear change in spring, thus reducing labour costs; the coating process should be refined so that Velcro closures of nets do not become sealed shut.     

Influence of the type of collector and collector preparation periods on the settling rate of the scallop Nodipecten nodosus L. in the laboratory

We analysed the settling rate of Nodipecten nodosus L. scallop spats during winter and spring, testing different types of collectors and collector preparation periods. Larval rearing was conducted with water exchange every 48 h, density at 2 larvae mL⁻¹ and feeding between 0.5 and 2 × 10⁴ microalgae cellsmL⁻¹. The recovery larvae based on D-larvae produced were 31.6% (Winter Trial) and 47.2% (Spring Trial), without any antibacterial additives. The mean settling rates obtained in Winter Trial were from 0.04% to 0.79% withstand in Spring Trial were 24.99–48.65%. In the Winter Trial, there was no statistical difference between the settling rate of collectors prepared for 6 or 12 days. The settling rates of the netlon collectors with pine leaves were up to 19 times higher than those of the other types of collectors. In the Spring Trial, there was no statistical difference between the settling rates of the netlon and plastic net fruit collectors. Collectors with pine leaves produced a yield of spats up to 48.65%, more than those without pine leaves ( P <0.01). The efficiency of larval rearing and settling obtained in spring, pine leaves and low-cost local material indicate the feasibility to improve and facilitate regular production of N. nodosus spats for promotion of the growth of scallop culture in Brazil.     

Growth,survival and immune activity of scallops,Chlamys farreri Jones et Preston,compared between suspended and bottom culture in Haizhou Bay,China

We examined the growth, survival and immune response of the scallop, Chlamys farreri, during a 1‐year period in deep water of Haizhou Bay. Scallops were cultured using two methods: (1) in lantern nets at a 5 m depth and (2) in a bottom culture system (sleeves) on the seabed at about a 25 m depth. Shell heights, meat dry weight and immune activities in the haemolymph (superoxide dismutase and myeloperoxidase) were measured bimonthly or quarterly from July 2007 to June 2008. Survival was measured at the end of the study and environmental parameters in the experimental layers were monitored during the experiment. The growth and immune activities of scallops were lower when the water temperature was high, which was consistent with the main mortality occurring in summer. The growth and immunity of scallops were higher in the suspended culture than in the bottom culture during the experiment, with the exception of shell growth during the last study period. Survival of scallops in the suspended culture (54.6±12.3%) was significantly lower than that in the bottom culture (86.8±3.5%) at the end of this study. We conclude from our results that the high mortality of C. farreri can be prevented by culturing them in a bottom culture system before November of the first year, and then transferring them to a suspended culture to improve scallop production.     

提高海湾扇贝虾池保苗成活率技术研究

利用６５亩虾池进行提高海湾扇贝保苗成活率技术研究，入池稚贝２．１亿粒，经４３天暂养，出池商品苗９７２０万粒，成活率达４６．３％，纯益３５．８４万元。而海上保苗成活率仅为１０％左右。１９９４年２月，专家鉴定认为，本研究居国内先进水平。     

Utility of high-density plantings in bay scallop, Argopecten irradians irradians, restoration

Two different methods of establishing high-density spawner sanctuaries for bay scallop (Argopecten irradians irradians) restoration were evaluated over 2 years at a site in Northwest Harbor, East Hampton, New York, USA. Hatchery-reared scallops, which had been overwintered at nearby sites, were free-planted directly to the bottom in late March/early April at an initial target density of 94?C128 scallops/m². In addition, scallops were stocked in off-bottom culture units consisting of three vertically stacked 15-mm mesh ADPI^® bags at densities of 50, 100, or 200 scallops/bag (=117, 234, or 468 scallops/m²), respectively. Survival of scallops differed significantly by year, planting method, and scallop source. Survival of free-planted scallops was generally lower than caged scallops. Better survival of free-planted scallops in 2005 versus 2006 likely reflected the presence of luxuriant eelgrass beds in 2005, which were absent in 2006. Survival of scallops in ADPI bags was not appreciably related to stocking density. Shell growth was highest for free-planted scallops; in cages, growth was somewhat better at 50 versus 200 scallops/bag. Wet weights of epibionts were significantly higher in caged versus free-planted scallops. Reproductive condition of scallops stocked at 50/bag was usually higher than at 200/bag. Both free-planting and off-bottom systems yielded high densities of adult bay scallops at the time of spawning, which ensures a higher probability of successful fertilization of spawned eggs and thus a greater potential for success of restoration efforts.     

Incidental catch and discard of red drum, Sciaenops ocellatus, in a large mesh Paralichthyidae gillnet fishery: experimental evaluation of a fisher's experience at limiting bycatch

Abstract  The ability of a commercial fisher to limit red drum, Sciaenops ocellatus (Linnaeus), bycatch was evaluated by comparing the catch of directed sets (net site chosen by the commercial fisher) vs randomly placed gillnets during 70 days of gillnetting ( n  = 691 sets). Catch rate did not differ between directed sets and nets set randomly. Thus, fisher experience did not lead to reduced bycatch; however, this may have been influenced by overall low red drum bycatch (0.41 fish net⁻¹ for 12 h sets and 0.59 fish net⁻¹ for 24 h sets). Catch rates of southern flounder were much higher at 3.97 and 3.37 fish net⁻¹ for 12 h and 24 h sets, respectively. Fishing 10 nets per day, the catch of red drum exceeded the daily bag limit of seven red drum on 23% of the days. Of the 326 red drum retrieved from gillnets, 32.5% were dead at the time of retrieval; but only 15 of the 106 dead red drum had to be discarded due to size limits, and six were discarded dead based on bag limits. Current fisheries management regulations (bag limit and window limit of 457–686 mm) are supported by these findings given the conditions (e.g. red drum densities) at which the study was performed.     

Effects of temperature, density and early weaning on the survival and growth of Atlantic ditch shrimp Palaemonetes varians larvae

This investigation examined the effects of temperature, density and early weaning on the survival and growth of Palaemonetes varians larvae. Survival of larvae raised at 17.5 °C was not significantly different (average + standard deviation) (94 ± 5%) from the survival of those raised at 19.5 °C (95 ± 5%) and at 21.5 °C (94 ± 4%). However, the duration of the larval stage was significantly longer for shrimp reared at 17.5 °C (17.3 ± 0.8 days) compared with shrimp reared at 19.5 °C (14.3 ± 0.7 days) and at 21.5 °C (11.3 ± 0.6 days). No significant differences ( P >0.05) were found in the survival rate, final weight and length of larvae reared at the densities of 5, 10, 20 and 50 larvae L⁻¹. The survival of P. varians larvae fed solely on Artemia was significantly higher ( P <0.05) than larvae weaned with an artificial practical diet from Zoea II stage (94 ± 4% and 82 ± 1%, respectively, for Artemia and artificial diet-fed larvae), but no significant differences ( P >0.05) were observed in the final larval weight or length between these two treatments. The survival and growth of the larvae fed with the practical diet tested is a promising step ahead in the development of the culture of this species as it eliminates both the need for Artemia throughout all larval stages, and the need for more expensive artificial diets.     

Analysis of mesh breaking loads in cotton gill nets: Possible solution to ghost fishing

ABSTRACT:   A small number of fishers in Chiba Prefecture of eastern Japan use cotton gill nets to catch Japanese spiny lobster Panulirus japonicus. To examine the advantages of cotton gill nets, we analyzed changes in mesh breaking load of a new cotton gill net used in a fishing operation. A new cotton gill net was also soaked in a seawater tank to simulate ghost fishing conditions. The average mesh breaking load of new cotton mesh was 50.3 N. This value decreased to 19.0 N after 38 days (∼912 h), and after 82 days (∼1968 h) the mesh could be easily torn (breaking load 0.07 N). Under fishing conditions, the cumulative soak time was only 744.4 h over 19 months. The average breaking load at the end of this period was 43.1 N, a strength 86% that of the presoaked mesh. The mesh breaking load of a cotton gill net continuously soaked for 744.4 h was 26.1 N, as estimated from tank experiment data. Thus, a cotton gill net maintains reasonable strength under typical use conditions, but will degrade if lost at sea.     

Effect of cold shock and hormone on growth and male morphotypes of freshwater prawn,Macrobrachium rosenbergii (de Man)

A study was carried out to determine the effects of cold shock and 17α‐methyl testosterone hormone on growth in male morphotypes of giant freshwater prawn Macrobrachium rosenbergii. Juvenile males were exposed at 18 ± 0.25°C for 24 h with normal feed and cultured at 27 ± 0.7°C for 70 days as well as administrated feed with hormone separately at 400 mg kg^?1 feed for the first 30 days of culture period (70 days). The growth (Mean ± SD) of male juveniles at harvest was closely homogenous in the cold shock (CLS) treated group; while it was heterogeneous in hormone‐treated (MH) and control (CO) groups. Although total body weight of blue claw (BC) males was not significantly different in the controls and the treatments, the 2nd pereiopods (claw) weight and length of the BC was significantly lower in CLS (0.52 ± 0.05 g, 10.02 ± 0.65 cm) than that in the CO (0.71 ± 0.16 g, 12.53 ± 0.57 cm) and MH (0.75 ± 0.08 g, 12.85 ± 1.18 cm) treatments. Survival of prawns was similar in treatments. The morphotypes of male prawn were significantly different with 59% of BC males with small‐sized claws in CLS and, 45% and 30% of BC males with large‐sized claws in MH and CO respectively. Cold shock adversely affected male morphotypes of the prawn so that numbers of BC males with small‐sized claw was the highest in CLS tank. However, the CLS treatment resulted in more uniform marketable prawns and suggested a high production of BC males in an all‐male culture system.     

Use of biological reference points for the conservation of Atlantic salmon, Salmo salar, in the River Lune, North West England

Abstract  The development and use of biological reference points (BRPs) for salmon, Salmo salar L., conservation on the River Lune, England were examined. The Lune supports recreational and net fisheries with annual catches averaging 1332 and 2146 salmon, respectively. Using models transported from other river systems, BRPs were developed that were exclusive to the Lune; specifically the number of eggs deposited and carrying capacity estimates for age 0+ and 1+ parr. The conservation limit was estimated at 11.9 million eggs, and to ensure that the conservation limit was exceeded 80% of the time, the management target was set at 14.4 million eggs (equivalent to ∼5000 adults). Between 1989 and 1998 the management target was exceeded in only 2 years. Comparison of juvenile salmon densities in 1991 and 1997 with estimates of carrying capacity indicated that 0+ and 1+ parr densities were at around 60% of carrying capacity and may relate to the number of eggs deposited in 1990 and 1996 being approximately 70% of the target value. From, and including, the 2000 fishing season, regulations to ensure that the conservation limit is met 4 years out of 5 were introduced. These consisted of a reduction from 26 to 12 haaf nets, from 10 to seven drift nets and a four-fish bag limit for the rod fishery. In the period between 2000 and 2004 there was a marked increase in the estimated number of salmon spawning and the management target value of ∼5000 spawning adults was exceeded in all years. There was also an increase in the juvenile salmon population. The estimated level of exploitation in the net and rod fisheries reduced from 29.9% to 13.8% and from 26.4% to 14.8% respectively, after the introduction of the regulations.     

Polyculture of sea scallops (Placopecten magellanicus) suspended from salmon cages

Commercial and developmental operations for the culture of the seascallop, Placopecten magellanicus, are present in AtlanticCanada and New England. In an experiment designed to examine the commercialfeasibility of polyculture of scallops with Atlantic salmon(Salmo salar), we measured growth andsurvival of sea scallops grown in suspension at two salmon aquaculture sites innortheastern Maine (Johnson Cove (JC) and Treats Island (TI)). Sea scallop spatwere grown in pearl nets and deployed on drop lines containing ten nets inAugust 1994. One drop line of ten nets was sampled about every four months andscallops were counted, measured and weighed. Scallop tissues were also analysedfor paralytic shellfish toxins (PSP). The maximum level of PSP recorded duringthe study was 1174 g STX equiv.·100 gtissue^–1 (excluding adductor muscle weight). After one year,shell heights were 53.6 and 56.4 mm, growth rates were 0.11 and0.12 mm per day and wet adductor muscle weights were 3.3 and 4.1g (TI and JC, respectively). These growth rates were comparable tosea scallops grown in suspension culture to a nearby scallop aquaculture siteand other areas in Atlantic Canada. Reduced rates of survival were found duringthe latter part of the experiment and were attributable, in part, to heavyfouling, predators and high stocking density. The potential for supplementalincome, diversification of the salmon aquaculture industry, and feasibility ofculturing scallops at adjacent sites to salmon operations does exist.     

Reproduction of hatchery-reared and transplanted wild bay scallops, Argopecten irradians irradians, relative to natural populations

Efforts to restore bay scallop populations in the United States throughtransplantation of wild stock and reseeding of hatchery-reared individuals haveincreased due to declines in natural populations, yet little is known of thecomparative spawning patterns and relative reproductive investment of thesedifferent groups. In this study, spawning patterns of wild scallops from asource population in Northwest Harbor, New York and of scallops transplanted toa distant site in the same embayment (Flanders Bay) were similar.Hatchery-reared scallops held in pearl nets in Hallock Bay, New York showed thesame temporal spawning pattern and level of reproductive investment as scallopsfrom adjacent wild populations and wild scallops held in pearl nets. We suggestthat hatchery-reared scallops may be equally valuable as potential broodstockfor reseeding operations as wild scallops of the same size, provided thatappropriate conditioning and rearing practices are maintained. Both wild andhatchery-reared scallops may be transplanted a short period (i.e. 2–4weeks) prior to expected spawning to provide a source of potential broodstockinareas where natural population densities are low.     

The culture of the southern bay scallop in Tampa Bay, an urban Florida estuary

Bay scallop, Argopecten irradians concentricus (Say), stocks were collected from a Homosassa (Florida) population in 1991 and were kept in seawater from Bayboro Harbor on Tampa Bay, an urban Florida estuary. They were fed with Isochrysis galbana and Tetraselmis sp. Spawning was allowed to occur after the scallops became ripe. The hatching rate of the F1 eggs to D-shaped larvae was 72%. Settlement and metamorphosis began 11 days after fertilization. When spat reached a shell height of 0.8 mm in the laboratory, they were placed with substrates into 300 and 800 m mesh bags, and later in lantern nets, suspended from a dock in Bayboro Harbor. The F1 scallops successfully survived to gonad maturity in the fall of 1992, with mean (sd) shell height of 49.8 (4.0) mm on 6 September 1992. The scallops experienced heavy mortality during the summer, partially as a result of heavy fouling. From early August to October of 1992, F1 scallops grown in Bayboro Harbor were successfully spawned in the laboratory. Growth and survival of the F2 scallops were comparable to those of the F1 scallops. Results have shown that bay scallops can complete an entire life cycle in an urban estuary such as Tampa Bay, and a hatchery for bay scallops on the estuary can assist in the restoration of the population. Fouling represents a possible severe limitation and alternatives to caging for grow-out should be considered.     

The effects of epibionts and predators on the growth and mortality rates of Argopecten purpuratus cultures in southern Chile

Epibiont and predator effects on the growth and mortality of the northern scallop Argopecten purpuratus were evaluated in cultures in southern Chile.The most common epibionts were bryozoans, hydrozoans and algae in both study sites, Metri Bay (41°36; 72°43W) and Chidhuapi Channel (41°49S; 73°05W).After 12 months of culture in pearl nets and lantern nets, the scallops size did not show statistically significant differences in cultures with and without epibionts in both study sites nor were there differences in the growth either with or without the presence of predators (decapod crustaceans). The growth rate was higher in Chidhuapi Channel than in Metri Bay.Mortality was concentrated in the initial phase of culture in pearl nets. During the culture phase in lantern nets, the mortality rate was lower than 3%. The mortality rate in scallops with epibionts was higher than when these were removed in the culture phase in pearl nets. In Metri Bay the mortality rate with predators was higher than without predators. Epibionts and predators did not affect mortality in the culture phase in lantern nets.Epibionts and predation are important factors in the early mortality of scallops and therefore in the success of culture. Epibiosis, however, is not important in scallop growth in southern Chile. This is related to the composition of the epibionts and to the low temperatures which probably limit the growth of algae and invertebrates.     

Growth and production of endangered Indian butter catfish,Ompok bimaculatus (Bloch) at different stocking densities in earthen ponds

Growth, survival and production of endangered Indian butter catfish (Ompok bimaculatus) fingerlings were examined at different stocking densities. The experiment was conducted for 8 months in nine earthen ponds having an area of 0.03 ha each. 30‐day‐old fingerling, stocked at 40 000 ha^?1 was designated as treatment‐1 (T1), 50 000 ha^?1 as treatment‐2 (T2) and 60 000 ha^?1 as treatment‐3 (T3). At stocking, all fingerlings were of same age group with a mean length and weight of 3.36 ± 0.08 cm and weight of 0.83 ± 0.02 g respectively. Fish in all the treatments were fed with a mixture of rice bran (50%), mustard oil cake (30%), fish meal (19%) and vitamin‐mineral premix (1%). Physicochemical parameters, plankton populations and soil parameters were at the optimum level for fish culture. Highest weight gain was observed in T1 and lowest in T3. Final length, weight and survival of fish also followed the same trend as weight gain. Highest specific growth rate was observed in T1 followed by T2 and T3. Feed conversion ratio was significantly lower in T1 followed by T2 and T3 in that order. Significantly higher amount of fish was produced in T1 than T2 and T3 respectively. Higher net benefit was obtained from T1 than from T2 and T3. Overall, the highest growth, survival and benefit of fish were obtained at a density of 40 000 fingerlings ha^?1. Hence, of the three stocking densities, 40 000 fingerlings ha^?1 appears to be the most suitable stocking density for culturing of Indian butter catfish in grow‐out system.     

Holding wild Snow crab,Chionoecetes opilio: effects of stocking density and feeding on survival and injury

In this study the effects of different stocking densities on survival, injury and weight of captive male snow crab were examined. The first experiment (I) was carried out in square plastic tanks (700 L) with stocking densities of 100 (L), 150 (M) and 200 kg m^?3 (H) for 30 days. In a second experiment (II) snow crabs were kept at a stocking density of 50 kg m^?3 and were either fed (F) or not fed (S) for the same period of 35 days. The last experiment (III), was carried out with stocking densities of 25 kg m^?3 for 21 days with two groups, one with inactivated claw and one without rubber bands, with three replicates per treatment. In the first experiment mortality (H = 27, M = 26 and L = 36%) and occurrence of injuries (H = 27, M = 20 and L = 16%) were high in all groups. The weight loss during the experimental period was; H = 15.3, M = 10.9 and L = 15.5 g, and was not significant different between the groups. In experiment II the mortality (F = 13% and S = 14%) and injuries were lower (F = 12% and S = 17%). The average weight increased in the fed treatment and decreased in the starved treatments. In the last experiment there was no mortality in any of the groups and the levels of injury were low (5% and 7%). The results show that adult male snow crab cannot be stored at densities equal to or higher than 25 kg m^?3 for 3 weeks without risk of mortality.     

On the relationship between low winter temperatures and mortality of juvenile scallops, Pecten maximus L., cultured in western Norway

The mortality of juvenile scallops (Pecten maximus L.) cultured at two densities at 8‐ and 15‐m depth was investigated at 17 trial locations along the western Norwegian coast between latitudes 58 and 65°N. During the winter of 1995/1996, scallops suffered high mortality at many sites. The results show a clear relationship between minimum temperature recorded on the sites and scallop mortality. All the scallops died at sites where minimum temperatures were lower than 2°C, while a mortality rate below 30% was only obtained at locations where the minimum temperature was 4–5°C. At temperatures between 2 and 4°C, mortality was intermediate, ranging from 52% to 100%. There were no mortality differences between culture densities, while a significantly higher mortality at 8‐ than at 15‐m depth was shown for two of the four sites with a total mean mortality lower than 30%. The results are discussed in relation to low‐temperature conditions along the Norwegian coast to suggest risk assessments for site selection in scallop culture.     

Effects of stocking density on intermediate culture of the razor clam Ensis arcuatus (Pharidae: Bivalvia)

Commercial production of most bivalve species involves a phase of intermediate cultivation during which juveniles are grown under protected conditions until they can be transferred to the final grow‐out location. Consequently, the aim of this study was investigating the effect of density on growth and survival in the intermediate culture of the razor clam Ensis arcuatus in raft. Two series of experiments were performed, using in the first experiment two holding systems: 5‐L plastic bottles and PVC cylinders, both perforated, covered with a 1 mm mesh net to prevent razor clam escape and a 10‐cm layer of coarse grained sand (300–1200 μm grain diameter). In this trial, two stocking densities were tested: 0.15 and 0.30 kg m^?2. In the second one‐two densities were essayed (0.62 and 1.24 kg m^?2) in the PCV cylinders. In the first experiment after 27 of trial higher growth in cylinders at low density was observed. At the end of this trial all juveniles died in the 5‐L plastic bottles and higher growth and survival were recorded in the cylinders at low density. In the second experiment, significant differences in growth and survival were found on day 70, with the best results at low density. Five‐L plastic bottles must be rejected as holding system for the intermediate culture of E. arcuatus and the PVC cylinders at low densities could be a good alternative. At the end of the experiment razor clams reached the adequate size for their transfer into the grow‐out system.