The status of the Delaware whelk dredge fishery was assessed from state landings reports and from data collected by an onboard observer. Mean annual whelk landings for 1994 to 2000 were 18.5 mt of meats and increased to 241.6 mt for the period 2001 to 2004. Annual landings for 2001 to 2003 were 88% to 119% of the sum of dredge and trawl fishery landings reported by the remaining states on the United States Atlantic coast. Although knobbed whelks, Busycon carica, are landed throughout the year, 88% of pooled monthly landings for 1994 to 2004 were taken between March and June inclusive. Eleven observer cruises were conducted March to June 2004. Total estimated daily take of legal (length ≥127 mm) knobbed whelks ranged from to 197–3,710 organisms. Expected catch rates were estimated at 83.2 legal knobbed whelks per hour per meter of dredge width. Dredges were generally towed parallel to bathymetric contours and adjacent to shoal features in 2–20 m depths. Estimates of the area of bottom dredged on each cruise ranged from 4.9–14.2 ha. At times, multiple boats were observed dredging the same bottom, suggesting a cooperative fishing technique. Seventy-nine percent of dredge tows occurred on bottom comprised of mud and sand, and mean numbers of knobbed whelks in 0.04 m³ samples were greatest from mud/sand habitats. Twenty-one taxonomic groups of organisms were observed in samples taken from dredges. Knobbed whelk and horseshoe crabs, Limulus polyphemus, dominated dredge catch by number. Whelks collected in the Atlantic Ocean were significantly larger than those collected in the Delaware Bay. Mean lengths of whelks collected in the Bay in 2004 were significantly less than lengths of Bay whelks collected in 1994 prior to the inception of the minimum length regulation. Shifts in size distribution and the cyclical nature of other whelk fisheries suggest that the elevated landings experienced during 2001 to 2004 are not sustainable.

The hard clam (Meretrix lusoria) is one of the most important cultured molluscs in Taiwan. Although it is mainly cultured in ponds and supplemental feeding of artificial feed is commonly practiced, no scientific information on its preferred foods and appropriate feeding strategies are available. Six diets: fishmeal (F), soybean meal (S), commercial hard clam feed (C), microalgae Tetraselmis chui (T) and Nannochloropsis oculata (N) and bread yeast (Y), were fed to hard clams. Each diet was fed at 3 concentrations (20 mg L⁻¹, 200 mg L⁻¹ and 633 mg L⁻¹) and was fed to clams of 3 sizes (7–11g, 12–17 g and 18–26 g total body weight) to gauge their effects on weight-specific filtration rate and pseudofeces production. Overall, the filtration rates for diets in descending order were S > C > F = Y > N > T. Particle size of the diets played an important, but not the only. role in determining the filtration rate. Diets with regular particle shape (N, T, Y) yield lower filtration rates and higher pseudofeces production than diets with irregular shape (C, F, S). Both filtration rate and pseudofeces production were higher for yeast than for algae (T, N). Filtration rate and pseudofeces production were also higher for the mixed component diet (C) than for single component diets (F, S). Filtration rate, but not pseudofeces production, was higher for the plant-based diet (S) than for fishmeal (F). Both diet concentration and clam size had inverse correlations with weight-specific filtration rate. The effects of all interactions between diets, diet concentrations, and clam sizes on filtration rates were significant, reflecting the complexity of feeding behavior of Meretrix lusoria.

We review the variety of methods that have been used over the last 50 y in the Former Soviet Union, Eastern and Western Europe, and recently in North America to determine growth rate and longevity in zebra mussels (Dreissena polymorpha [Pallas]). These methods include: counting annual rings, analysis of size-frequency distributions, following growth under experimental conditions and monitoring marked mussels under natural conditions, without removing them from substrate. The last method provides the most reliable data, however this is the least common method used. Dreissena polymorpha growth rates depend on water temperature, season of the year, location in the water column, food availability, oxygen concentrations, water velocity and various other environmental factors. However, it is very difficult to separate the independent effects of each of these factors, especially in natural waterbodies. Several factors may overlap and have additive or synergistic effect that makes it difficult to determine the effects of a single factor. When comparing among studies that used the same methods, we found that zebra mussels grow faster in reservoirs than in lakes. The reported longevity of D. polymorpha varies from 2–19 y and it is not clear to what extent this variation is caused by biological variability and environmental conditions and what amount of the variation is caused by the methods used to assess age and longevity.

As the number of native species targeted for aquaculture and enhancement in British Columbia (BC) rises, fisheries managers must develop policies and species-specific management plans that facilitate industry expansion while protecting the integrity and fitness of wild stocks. Whereas genetic introgression of domesticated stocks with wild stocks cannot be completely eliminated, some control can be gained by limiting the collection and culture of domesticated stocks to geographic units defined by the genetic structure of wild stocks. We describe the genetic structure of two species that are targeted for intensive enhancement and aquaculture in BC: Geoduck clams, Panopea abrupta and red sea urchins, Strongylocentrotus franciscanus. Based on a survey of eight polymorphic microsatellite loci, P. abrupta contained significant geographic structure within BC, with the distribution of genetic variation consistent with stepping stone gene flow under an isolation-by-distance model. A survey of seven polymorphic microsatellite loci covering a similar geographic range revealed genetic homogeneity of S. franciscanus in BC. Based on the different levels of structure displayed in the two species, we propose three geographically-based management units for P. abrupta and two for S. franciscanus in BC.

In the scope of expanding seeding operations of juvenile scallops (Placopecten magellanicus) around Îles-de-la-Madeleine (Quebec, Canada), this study assesses the influence of substrate on growth, survival, dispersal and predation rates in controlled experiments. Three substrates were tested: gravel, sand and sand with empty scallop shells (to investigate the feasibility of modifying the substrate as a management strategy). Dispersal rates were studied with a substrate choice experiment. Predation experiments with two major scallop predators, the rock crab Cancer irroratus and the sea star Asterias vulgaris, were carried out on different substrate types. No significant difference in growth was observed among substrates and no mortality was observed during the experiment. This suggests other factors, such as hydrodynamics, may be more important than substrate. The dispersal rate was significantly greater on sandy substrate, whereas gravel and sand–shells had similar results. Crab predation was lower on the more heterogeneous substrate (i.e., gravel) whereas, sea star predation was lower on sand. Modifying the natural sand substrate by adding scallop shells could improve seeding success because it diminishes dispersal and predation by crabs.

Two infaunal species, the purple clam Amiantis purpurata and the razor clam Solen tehuelchus, are common species in the 15–20 m sandy bottom sediments between southern Brazil and central Argentina. Both species are food sources for the coastal food web, but the extent of their contribution to this food web is still unknown. Based on stomach content analysis and δ¹⁵N and δ¹⁵C stable isotope signatures we explored the position of these clams in the food web. Stomach content shows that the ray Sympterigia bonapartei and the white croaker Micropogonias furnieri prey on entire A. purpurata and S. tehuelchus. The stable isotopic analysis confirms this result. The elephant fish Callorynchus callorynchus and the Brazilian codling Urophycis brasiliensis also show values of C and N consistent with those expected from species that are preying on A. purpurata. Based on the prediction from the isotopic analysis the clam A. purpurata is a food source for the shrimps Artemesia longinaris, Pleoticus muelleri, the anemone Antholoba achates and the gastropod Buccinanops monilifer. The gastropods Adelomelon brasiliana, Olivancillaria deshayesiana, Olivancillaria urceus and Zidona dufresnei also show evidence of consuming A. purpurata but with contribution from other species with heavier C content. According to complementary results the razor clam Solen tehuelchus may be this other species. The stable isotopic analysis shows that both clam species are at the base of the consumers in the food web. A. pupurata showed lighter C mark than S. tehuelchus, but the N isotopic mark showed higher value but still being within the same trophic level.

Light and electron microscopical studies were carried out to characterize the hemocytes of the oyster, Crassostrea ariakensis. Three types of hemocytes were recognized: granulocytes, large hyalinocytes and small hyalinocytes. The large hyalinocytes and small hyalinocytes were agranular cells. The large hyalinocytes presented thin cytoplasm and high nucleus: cytoplasm ratios. The small hyalinocytes were the most homogeneous in shape and showed round or oval. They have the highest nucleus: cytoplasm ratios and contained very thin cytoplasm. The granulocytes showed abundant cytoplasm and low nucleus: cytoplasm ratios. At the ultrastructural level, the large hyalinocytes cytoplasm contained a variable number of mitochondria, Golgi complex and endoplasmic reticulum. They showed a total absence of cytoplasmic granules or a few small electron-lucid vesicles of different sizes. The granulocytes showed more polymorphic than the agranular cells, with numerous pseudopodia sprouting off their surface. The granulocytes showed similar organelles, but on the contrary they had abundant electron-dense particles or electron-lucent granules in the cell cytoplasm. The small hyalinocytes presented a total absence of cytoplasmic granules and few organelles and only one or two mitochondria were sometimes observed in the cytoplasm. Total hemocyte counts gave a mean (±SE) concentration of 2.06 ± 0.20 × 10⁷ cells mL⁻¹ of hemolymph. Differential hemocyte counts identified the granulocytes as the predominant cell type, followed by the large hyalinocytes and the small hyalinocytes. The percentages of the three cell types in the hemocyte population of C. ariakensis were 68.4%, 21.6% and 9.0%, respectively. The quantitative study of phagocytosis showed that the granulocytes were phagocytic cells and the agranular cells showed a limited phagocytic ability. After the separation in Percoll density gradient, the granulocytes were separated from agranulocytes and pure granulocytes were obtained. However, the separation of different agranular cell types (large hyalinocytes and small hyalinocytes) was not achieved by Percoll or Ficoll gradient centrifugation. Our study provides a morphofunctional basis for the cellular defense mechanisms in C. ariakensis.

The Suminoe oyster, Crassostrea ariakensis, has been under investigation since the early 1990s for potential use in restoring the commercial harvest or for aquaculture of oysters in the Chesapeake Bay, USA. Initial studies focusing on C. ariakensis documented a significant level of tolerance to the protozoan parasite Perkinsus marinus, a pathogen found in almost all reaches of the Bay and widely acknowledged as one of the main reasons for the decline in the eastern oyster, Crassostrea virginica, harvest since the late 1980s. Crassostrea ariakensis was demonstrated to acquire P. marinus, however infection intensities, as measured using Ray's thioglycollate medium assay indices, generally were found to be light. As part of a series of experiments to study potential impacts on the Chesapeake Bay region of pathogens found in C. ariakensis in Asia, a challenge experiment was conducted to study the pathogenicity of Perkinsus olseni to C. ariakensis. During this study, we observed the acquisition of moderate and heavy infection intensities of P. marinus in triploid C. ariakensis oysters being maintained in the laboratory. Results suggest that there may be some risk of mortality from P. marinus if C. ariakensis is held under stressful conditions at least in hatchery or laboratory settings.

Shell height at age estimates from Suminoe (Crassostrea ariakensis) and Pacific (C. gigas) oysters from a natural oyster reef in Laizhou Bay, China were compared with shell height at age estimates from triploid C. ariakensis of known age from the Rappahannock River, Virginia. C. ariakensis and C. gigas reach shell heights in excess of 76 mm (3 inches) within 2 years after settlement regardless of the source location. This fast growth appears to continue through at least age 4 or age 5 in wild individuals, because the growth trajectories for both species had not reached asymptotic height in the oldest individuals collected. Estimates of the asymptotic maximum height (SH_max) from fitted Von Bertalanffy (VB) growth models were greatest for Chinese C. ariakensis (244.0 mm, standard error of the mean [SE] 30.4) and near the maximum shell height (227.0 mm) measured at the time of collection. Maximum shell heights measured on live Chinese C. gigas (173.0 mm) and Rappahannock C. ariakensis (190.0 mm) were also within the standard error estimates for the SH_max estimates from the fitted VB models for Chinese C. gigas (158.6 mm, SE 20.3) and Rappahannock C. ariakensis (183 mm, SE 19.1). Fitted VB growth curves were not significantly different between species within the same habitat, within species in different habitats or between species in different habitats. The ratio of shell height to shell width and shell height to shell inflation for triploid C. ariakensis was significantly less than similar ratios observed in wild C. ariakensis and C. gigas oysters.

Perkinsus (= Dermocystidium) marinus is a major cause of mortality in eastern oysters, Crassostrea virginica. Because initiation of infection and progression of disease are favored by high temperature and high salinity, we hypothesized that climatic cycles influence cycles of disease. Analyses of a 10-y time series of disease prevalence and intensity, chlorophyll a, suspended sediments, water temperature and salinity from a Louisiana site, using a wavelet technique, show a teleconnection between the El Niño-Southern Oscillation (ENSO) and oyster disease in the northern Gulf of Mexico. Salinity increases precede increased disease prevalence by several months. The changes in salinity that trigger changes in disease prevalence and intensity are strongly driven by ENSO events. Interannual variation is important in the initiation and intensification of disease, and salinity is the primary driving factor. The patterns in the environmental and disease time series suggest that epizootics can be initiated within 6 mo of a La Niña event, which produces increased water temperature and salinity. This relationship suggests an approach for predicting epizootics of P. marinus from climate models, which in turn can inform the management of oyster populations.

We conducted an arbitrary fragment length polymorphism (AFLP) analysis followed by tests of association to search for potential genetic markers associated with resistance to infection by Vibrio vulnificus and Perkinsus marinus in a sample of North Carolina oysters. We used 48 AFLP markers and found significant associations for two of these markers with the incidence of infection of P. marinus and two separate markers associated with the magnitude of infection of V. vulnificus. Further, there was evidence of epistatic interactions of genes affecting infection levels of both pathogens. This suggests existence of genes or groups of genes that are located on chromosome fragments close to the identified AFLP markers and that act directly or indirectly (through epistasis) to control the levels of infection by these microorganisms in oysters. The impact of the direct and epistatic effects of these unknown genes on infection level variability amounted to about 40% for both P. marinus and V. vulnificus. This study demonstrates the utility of the AFLP approach to identify genetic markers of pathogen/parasite resistance in eastern oysters. However, the identified AFLP markers are considered preliminary and suggestive only because of the limited sample size analyzed in this study. Further studies using this approach on a larger sample size are required to identify a set of robust molecular markers that would serve in a marker-supported breeding program designed to improve the quality of the oyster stock.

Munida subrugosa is the most abundant benthic species in the Beagle Channel (55°S, 68°W), Tierra del Fuego. Moreover, this species has two simultaneous but different feeding habits: predator and deposit feeder. Because of its high abundance (100 ind·100 m⁻²) and trophic position, this species plays a key role in the subantarctic benthic ecosystems. However, little is known about its energetic content and changes in dry mass during its reproductive cycle. Samples of M. subrugosa were obtained in 2000 to 2001 by means of an epibenthic trawl. The relative water content (WC) and the energetic content (EC) (kJ·g⁻¹ ash free dry mass [AFDM]) of whole adult animals, and the relative dry mass (RDM) and EC of tissues and organs of females were measured throughout one year. The EC investment of adults at the time of maximum gonadal development was evaluated. The EC was measured using a bomb calorimeter. The mean WC and EC for M. subrugosa was 59% ± 7% and 19 ± 2 kJ·g⁻¹ AFDM, respectively. WC and EC for whole adult animals varied significantly throughout the year, attaining maximum values in autumn or summer respectively, after the pattern of seasonal reproduction and feeding. Moreover, the EC of M. subrugosa varied by 30% annually. The RDM and EC investment in gonadal development was significant higher in females. The hepatopancreas in M. subrugosa is used as an energetic storage organ, because RDM and EC increased before vitellogenesis and moulting.

The effects of salinity, Na/K ratio and their interaction on growth, molting, nutrient retention and food conversion of Litopenaeus vannamei were investigated. The test shrimp were reared in artificial seawater and fed fresh polychaete worms, Neanthes japonica (Izuka) for 30 days. Two salinities (30 and 15 ppt) and 5 Na/K ratios (25.6, 34.1, 47.3, 102.1 and 153.3, mmol/mmol) were set, and each treatment had four replicates. During the feeding trial, the molting frequency (MF) was affected by neither salinity nor interaction effects, but Na/K ratio had an effect (P < 0.05). And there was a tendency that MF rose with the increment of Na/K ratio at both salinities. Final body weight, weight gain (WG) and specific growth rate (SGR) were significantly influenced by salinity, Na/K ratio and interaction effects (P < 0.05), whose mean values at salinity 15 ppt were significantly higher than those at 30 ppt. At 30 ppt, WGs and SGRs of shrimp exposed to Na/K ratio 34.1 and 47.3 were respectively more than 26% and 15% higher than of those exposed to the other ratios (P < 0.05), but no significant differences in growth were found among treatments at 15 ppt (P > 0.05). Na/K ratio and interaction effects significantly affected the nutrient retention (PR and ER), food conversion (FCE) and protein utility (PER) of the shrimp (P < 0.05), whereas salinity showed little impact. At 30 ppt, the PR and ER of shrimp exposed to Na/K ratio 153.3 were more than 30% lower than of those exposed to the other 4 ratios (P < 0.05); the FCEs of shrimp exposed to Na/K ratio 34.1 and 47.3 were more than 20% higher than of those exposed to Na/K ratio 25.6 and 102.1 (P < 0.05), and the FCE of shrimp exposed to Na/K ratio 153.3 was even lower (P < 0.05). At 15 ppt, no significant differences in FCE among treatments were found (P > 0.05). PER showed the similar tendency as FCE at both salinities. It was indicated that the shrimp were more adaptable to abnormal Na/K ratios at low salinity than at higher salinities, and good growth could always be obtained within a Na/K range of 34.1–47.3 (mmol/mmol) regardless of salinity.

This study examines the influence of feeding on digestive enzyme activities in the black tiger prawn, Penaeus monodon, using histological and biochemical techniques. Juvenile P. monodon (>50 mm total length) were sacrificed after feeding at sequential time intervals, with unfed controls also sacrificed at the same time intervals. Resin histology revealed that there were no morphological changes in the digestive gland F-cells between fed and unfed P. monodon over time. There were no significant changes in α-amylase specific activities in fed animals over time post feeding, nor were there any changes in starved animals through time. Trypsin and α-glucosidase activities were significantly higher in unfed animals than fed animals. There was a significant peak in α-glucosidase activities at 0 min post feeding but this could not be conclusively determined as an influence from feeding because of high variability and the near negligible levels of α-glucosidase activities. A peak in lipase activity was observed at 60 min post feeding, but because there was no significant differences in lipase activities between fed and unfed animals it was therefore inconclusive. Results from histological and biochemical analyses failed to prove that feeding had a significant influence on digestive enzyme production of P. monodon and suggest that digestive enzyme production in P. monodon may be continuous and is not strongly influenced by feeding.

Using the percentage of mature females as an index, the reproductive period of the brown shrimp, Farfantepenaeus californiensis, off the coast of Sonora in Mexico, has been shown to occur throughout the year with two peaks of mass spawning. The objective of this study is to determine if a similar reproductive period occurred off Agiabampo, at the Sonora-Sinaloa border. By combining 3 indices of mature females: size structure, abundance and fecundity at size, a single egg production index (EPI) was calculated. Monthly samples from January through December 2002 were collected during 5 continuous days around the full moon (full moon ± 2 days). Trawl net tows were used at depths from 1–9 m, 2 km north and south of the mouth of a coastal lagoon. Using the EPI, a single reproductive peak, May to August, was found, with May as the most important egg production month. On the other hand, the percentage of mature females showed a two peak reproductive period, one more intensive from May to August and the second one less intensive in November. We concluded that the best determination of the reproductive period of the brown shrimp required the use of three indices. Particularly off Agiabampo, this species has a well-defined reproductive period with just one massive spawning peak.

Domoic acid (DA) the toxin responsible for amnesic shellfish poisoning (ASP) has proven problematic for king scallop Pecten maximus fisheries and aquaculture in Ireland. Toxin concentration in hepatopancreas of individual scallops and composite samples of gonad and adductor muscle of scallops suspended from a submerged longline, 2 m beneath the water surface and on a seabed site, 12–15 m beneath the suspended scallops were monitored from February 2003 to February 2004 at an aquaculture site in Clew Bay, Ireland. DA concentration in hepatopancreas of scallops from the seabed and longline peaked in April 2003, individual concentrations reaching 1037.1 μg·g⁻¹ and 1212.6 μg·g⁻¹ respectively. No statistically significant differences were exhibited between DA concentration in hepatopancreas of seabed and longline scallops except on 1 of the 10 sampling occasions. Slow depuration of DA toxin from hepatopancreas occurred from April 2003 to June 2003 and the concentration remained relatively stable from June 2003 to Feb 2004. Interpretation of DA concentrations in gonad were complicated by the lower concentrations recorded and the variable size of the gonad caused by the reproductive cycle over the 12-month study duration. DA concentrations in adductor muscle were below the limit of detection throughout the investigation. In summary DA concentration between scallops held in suspension or maintained on the seabed exhibited minor difference, and routine monitoring samples could be collected annually and held in suspended culture systems rather than using more expensive diver collection for sample procurement.

Typical operating procedures used in the wild harvest pearl aquaculture (Pinctada maxima) industry in Western Australia are described as a basis for examining the potential environmental impact of the industry. A risk analysis workshop was held, which included industry representatives, marine scientists, regulatory agencies and conservation interests. The goal of the workshop was to document the main potential environmental and ecological risks that arise from the various activities carried out by the P. maxima industry. Thirteen environmental and ecological issues were identified across the P. maxima fishery. None were considered to be high risks; all were ranked as either moderate (23%) or low (77%). Moderate risk rankings included: introduction of disease from seeding; attraction of other fauna and introduction of exotic organisms. Low risks were: spread of disease; introduction of disease from hatchery; introduction of disease from translocation; impact to protected and endangered species resulting from entanglement; impact of habitat; impact to protected and endangered species resulting from farm lighting; nutrient impacts in sediment; perceived change in water quality; potential for litter and reduction of primary productivity. The low ratings given to disease risks took into account current strict regulatory controls for minimizing disease risks. The industry is considered to be environmentally benign. However, recommendations are made on how to further minimize risk.

Abalone aquaculture is dependent on cultured algae to induce larval settlement and as a food source for the early life stages of abalone until formulated feed or macroalgae such as Macrocystis sp., Porphyra sp. and Ulva sp. are introduced into the growout system. In the natural environment, abalone larvae settle on coralline red algae, which provide one of the strongest and most consistent settlement cues available for abalone larvae. However, propagation of coralline red algae is not practical commercially. Abalone farms in Japan successfully settle abalone larvae (Haliotis discus hannai) on the green alga Ulvella lens. U. lens also proved to be suitable to enhance settlement of cultured southern Australian abalone species (Haliotis laevigata, H. rubra). Most abalone farms in Australia are now growing U. lens for that purpose. U. lens is easy to culture, no specific facilities are needed and the alga can be grown on PVC settlement plates in commercial nursery tanks. However, U. lens has limited value as a feed for young postlarvae. Instead, cultured diatoms can be added after larvae successfully settle and start feeding. Juvenile abalone (>3 mm in shell length) can consume U. lens and grow rapidly on this alga. Diatom cultures and biofilms developing on settlement plates are not axenic and the role of bacteria in early postlarvae feeding is poorly understood. It has been suggested that bacteria may perform metabolic activities in the undeveloped gut of young postlarvae. At later stages of the nursery phase it becomes increasingly difficult to maintain adequate feed on the plates and this is still regarded as a significant bottleneck for the abalone aquaculture industry. Recent investigations have indicated that sporelings of macroalgae like Ulva sp. or diatoms that can provide more biomass may provide a suitable additional food source for juveniles (>3 mm in shell length).

Pearl oysters (Pinctada imbricata) were held in the laboratory and exposed to various levels of the heavy metals lead and zinc and the aliphatic hydrocarbons hexadecane and octacosane for 2 months. Individual oysters were followed over the course of the experiment, allowing specific calculation of total oyster growth (wet weight) and shell growth. Significant reductions in total oyster growth were observed when oysters were exposed to high concentrations (270μg L⁻¹) of either zinc or lead. Exposure to the aliphatic hydrocarbons had no effect on total oyster growth. High concentrations of lead completely halted shell growth, the first demonstration of pollutant induced cessation of biomineralization in pearl oysters. Conversely, exposure to moderate levels of lead and the long-chain hydrocarbon octacosane resulted in significant increases in shell width growth. The results from this study indicate that P. imbricata is relatively tolerant of the selected pollutants and could be deployed within a remediative context in moderately polluted coastal areas.

The recreational Roe's abalone fishery is concentrated on easily accessible reefs that adjoin metropolitan Perth in Western Australia. There is a restricted recreational fishing season of 1.5 h a morning, for six consecutive Sundays in November and December each year. The reefs near Perth are also the focus of the commercial Roe's abalone fishery in Western Australia. The recreational catch and effort for each 10 nautical mile section of the Perth fishery is estimated from a creel survey with instantaneous counts, aerial surveys and interviews with fishers, from 1997–2003. Most of the recreational and commercial catches were taken from small areas of the fishery, with approximately 87% of the recreational catch coming from two 10 nm sections, and 98% of the commercial catch coming from these two and one additional 10-nm section. An annual quota of 36 t limits the commercial catch, whereas estimates of the recreational catch increased from 33–51 t between 1997 and 2003. Recreational catch and effort estimates from 1999 on were corroborated by an independent telephone survey, with independent estimates falling within the 95% confidence intervals.

Silver-lip pearl oyster (Pinctada maxima) spat surveyed in the Eighty Mile Beach section of the North West Shelf have been used in conjunction with outputs from a particle dispersion model to identify likely spawning grounds. The dispersion model consisted of a 3-dimensional regional circulation model in which large numbers of individual particles were tracked over the period 1994 to 1999. From the settlement areas defined by the spat data, larvae were tracked back in time over their estimated pelagic phase of 24–31 days within the main spawning period of mid October to late December. The reverse calculation was also undertaken looking at larval dispersion from known broodstock populations. Results demonstrate that large tidal currents in the region move larvae back and forth across the shelf, whereas lower frequency currents influence their net transport. Whereas some model larvae traveled more than 60 km, most were transported less than 30 km. The model results suggest that spawning in the Eighty Mile Beach region is concentrated around the recently surveyed broodstock distribution between 8 and 15 m depth, with potential smaller contributions from the northeast. These spawning events are likely to lead to successful recruitment locally and alongshore to the southwest. They also feed larvae into neighboring shallow coastal environments (through tidal oscillations) and deeper waters to the west (~20 m). However, spat abundances seem to be low in these areas, suggesting that recruitment is strongly limited by habitat availability and possibly high mortality rates in shallow water. High local abundances of broodstock and spat observed occasionally in deeper water (~30 m) seem to be supported by intermittent larval transport from inshore populations. However, spawning in this area seems to contribute little to recruitment in the inshore populations.

Managing the broodstock conditioning process is important to the successful establishment of an abalone industry that can reliably produce juveniles from captive stock and pursue selective breeding. Four conditioning periods of 6, 8, 10 and 12 wk intervals were tested with captive greenlip abalone (Haliotis laevigata), using a constant conditioning temperature and ambient temperature as a control. The conditioning periods of 6, 8, 10 and 12 wks are equivalent to ~420, 560, 700 and 840 EAT (effective accumulative temperature), based on a biological zero point (BZP) of 6.9°C for gonad development. Greenlip abalone broodstock collected from the wild (87.5–142.1 mm in shell length and 108.2–482.8 g in whole weight) were spawned in all seasons including numerous induced spawnings outside of the normal breeding period with conditioned stock. Over the whole trial period, greater egg production from prescheduled spawnings occurred in the conditioned group with an average of 1.70 × 10⁶ eggs per tub of 5 female abalone per planned spawning, compared with abalone held in ambient control tubs that only produced an average of 0.40 × 10⁶ eggs per tub. Animals that were spawned every 8 wks produced the largest average number of eggs per holding tub, however, there was very little difference between conditioning periods in terms of number of successful spawnings per spawning round. The egg production for all planned spawnings was highest before the “natural spawning season” for greenlip abalone. In comparison, the highest numbers of unplanned spawnings occurred around the natural spawning period for the conditioned and control groups. Handling abalone did reduce egg production within the trial, but this was not statistically significant. Histological examination showed that using the visual gonad index is not a good indication of maturation of the abalone and confirmed that abalone can be conditioned out of season.

Both nutrient provisioning of eggs, during development within the ovary, and egg diameter are believed to be important factors governing the development and survival of invertebrate larvae. The diet of female broodstock and the conditioning regimen are likely to influence these parameters. In this study we examine the effect of broodstock diet (three formulated diets differing in levels of the fatty acid, Arachidonic acid [ARA], and a red seaweed diet) and spawning frequency on egg diameter variability both within a batch of eggs spawned from one female and between batches of eggs. Greenlip abalone broodstock were spawned at the beginning of the experiment and again every 16 wks (1131°C days effective accumulative temperature [EAT]) using commercial hatchery practices. The variability of egg diameter within batches spawned from the same female over three consecutive spawning rounds and within diet treatments was determined. Cytoplasm diameter, vitelline layer and jelly coat thickness of unfertilized eggs were also compared between eggs spawned from individual females and between females. In addition, the relationships between broodstock parameters (weight and shell length) and egg diameter were explored. Eggs spawned from females feeding on a red seaweed diet were smaller than eggs from the low ARA treatment. Depending on spawning frequency, broodstock diet can influence the cytoplasm diameter and jelly coat thickness. No relationship between egg diameter and broodstock parameters was found. However, batches spawned from the same female abalone became more variable over time with a shift in size frequency distribution. Results indicate that the variability of egg diameter within a batch changes from female to female and highlights the importance of selecting successful broodstock for conditioning at commercial hatcheries.

Growth, mortality, recruitment and sex-ratio of wild stocks of the silver-lipped pearl oyster Pinctada maxima were studied at sites spanning the geographic extent of the commercial fishery using mark-recapture experiments, recruitment cohort analysis and research surveys of stock abundance and reproductive status. Growth parameters (L_∞, K) from the von Bertalanffy growth equation were estimated at 210 mm dorso-ventral measurement (DVM) (±16 mm SD) and 0.74 at the Lacepede Islands, L_∞ of 199 mm DVM (±6 mm SD) and K of 0.79 on 80 Mile Beach, and L_∞ of 194 mm (±6 mm SD), and K of 0.72 at Exmouth Gulf respectively. Estimates of natural mortality (M) by tagging were very low (0.02–0.03), compared with catch-curve analysis, which estimated M to be between 0.1 in deeper (30–34 m) populations and 0.18 in shallow (9–12 m) populations. Settled P. maxima spat (0 and 1 age classes) on adult shell were quantified (e.g., 1,317 spat found on 119,000 shell in 2003) to obtain an annual recruitment index, which showed clear temporal trends in abundance. Over 7 y (1992 to 1995; 2001 to 2003) the annual recruitment index varied from 5.1–8.0 spat per 1,000 shell for the 0 age class, and 3.5–6.2 spat per 1,000 shell for the 1 age class. Preliminary predictions of future abundance showed promise, however more work is required on spatial and habitat effects on spat settlement before the potential of the 0 and 1 recruitment indices can be realized. We also confirm that Western Australian populations of P. maxima are protandrous hermaphrodites, with a 50:50 sex ratio not achieved until females are 170 mm DVM, which is above the maximum size fished.

The diverse and often complex essential components of successful marine stock enhancement are briefly reviewed. Progress on a project to enhance the New South Wales blacklip abalone (Haliotis rubra) fishery is discussed to demonstrate that for sedentary reef invertebrates such as abalone, successful enhancement entails an understanding of recruitment and production limiting factors. These include age and size specific growth and mortality rates. These variables encompass the influence of other species within reef ecosystems, especially predators and species that compete directly with them for space, shelter and food. This discussion is also used to demonstrate that such difficult projects can be facilitated and refined using a simple bio-economic model centered on two interdependent tasks. The first is to minimize net costs per unit of additional sustainable production generated by enhancement. The second is to determine the minimum amount of additional sustainable production required to render a project cost-effective. This first task has, as expected, proven complex and its resolution protracted and expensive, requiring innovative biotechnology and a comprehensive knowledge of the natural biology of blacklip abalone. This discussion principally reflects the perspective of the direct potential beneficiaries of abalone fisheries enhancement, namely commercial and recreational fishers and does not deal extensively with wider views and interests of other stakeholders, namely relevant government agencies and NGOs and the general public.

The tropical abalone, Haliotis asinina, is an ideal species to investigate the molecular mechanisms that control development, growth, reproduction and shell formation in all cultured haliotids. Here we describe the analysis of 232 expressed sequence tags (EST) obtained from a developmental H. asinina cDNA library intended for future microarray studies. From this data set we identified 183 unique gene clusters. Of these, 90 clusters showed significant homology with sequences lodged in GenBank, ranging in function from general housekeeping to signal transduction, gene regulation and cell-cell communication. Seventy-one clusters possessed completely novel ORFs greater than 50 codons in length, highlighting the paucity of sequence data from molluscs and other lophotrochozoans. This study of developmental gene expression in H. asinina provides the foundation for further detailed analyses of abalone growth, development and reproduction.

Mollusc culture, particularly the cultivation of pearl oysters, is an important component of the aquaculture industry in Western Australia. As a result, there has been a long-term investment in surveys of commercial mollusc species for potential diseases of concern. A number of pathogens, particularly haplosporidans, identified within wild-stock shellfish have the potential to adversely affect mollusc populations. Others pose risks for translocations associated with aquaculture. The microsporidan Steinhausia mytilovum (Field), found in ova of the blue mussel Mytilus galloprovincialis (Lamarck), poses intriguing questions about the origin and dispersal of its host.

Germlings of the green alga Ulva sp. were developed as a diet for juvenile Haliotis laevigata (≥3.5 mm shell length) and compared with a current commercial diet consisting of Ulvella lens plus the diatom species Navicula cf. jeffreyi. The utilization of macroalgae germlings (juvenile gametophyte and sporophyte) allowed 3-dimensional growth and subsequently provided greater feed biomass in comparison with the current 2-dimensional commercial feed for the later nursery phase consisting of 5–10 mm (shell length) juvenile abalone. The juvenile abalone showed active feeding on both the Ulva germling diet and the current commercial diet. The Ulvella lens/Navicula cf. jeffreyi diet resulted in abalone of significantly larger shell length at the end of the 14-wk feeding trial. However, the Ulva germling diet recorded significantly larger abalone for the first 4–5 wk, whereas the commercial diet produced significantly larger abalone from week 6 to the end of the trial. The growth rate on both diets exceeded 100 μm.day⁻¹ and the specific growth rates were maintained above 1%.day⁻¹ for the duration of the feeding trial with neither measure portraying significant differences between diets. There was no significant difference in juvenile abalone mortality feeding on the two diets. The Ulva germling consumption exhibited a spike (500 germling blades.abalone⁻¹.day⁻¹) in consumption at week three then, once reduced, a gradual increase occurred until the end of the trial. Ulvella lens consumption demonstrated a similar pattern to Ulva germlings consumption and was significantly, positively correlated. Consumption rates for the two green algae both correlated with juvenile abalone growth. The diatom (Navicula cf. jeffreyi) consumption was affected by plate rotation (light intensity and grazing pressure) rather than juvenile abalone.

This study reports growth rates estimates for Hexaplex (Trunculariopsis) trunculus (Gastropoda: Muricidae) from mark/recapture experiments carried out in the Ria Formosa lagoon (Algarve coast, southern Portugal). A total of 726 specimens (shell length and total weight ranging between 20.65–58.36 mm and 0.86–19.89 g, respectively) were marked with Dymo tape tags and released into a fish culture earth pond. During the marking process, no adverse effects on the whelks' health and behavior or immediate postmarking mortality were detected. Periodical recapture operations were undertaken using a traditional fishing gear designated locally as “wallet-line” and by hand gathering by scuba divers. A total of 170 whelks were caught, with a total of 216 recaptures (shell length and total weight ranging between 36.22–65.97 mm and 4.42–27.35 g, respectively), thus corresponding to a recapture rate of 29.8%. Despite the loss of one tag, all remaining tags were intact and easily readable. Marked individuals presented low monthly growth rates, in terms of shell length (1.0 mm/month or 2.3%/month), shell perimeter (2.0 mm/month or 3.1%/month) and total weight (0.7 g/month or 10.8%/month), which were highly variable between individuals and higher in smaller specimens. Data were used to estimate the von Bertalanffy growth parameters (length and weight) (K = 0.41, L_∞ = 82.76, W_∞ = 49.97 and t₀ = −0.05). The growth rate of T. trunculus was compared with results obtained in similar studies with other gastropod species to evaluate its potential for molluscan aquaculture.

No Abstract available.