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The ecosystem of Bandon Bay, in the Gulf of Thailand (GoT), has been impacted since 2007 by the continued stocking of larval blue swimming crab Portunus pelagicus, also called a crab bank. In this study, the food web in the Bay was modelled using Ecopath software to compare the trophic status, interaction and energy flow among the components in the system in 2007 and 2016 (i.e., before and 10 years after the crab bank intervention). The models were based on data collected from trawling. Twenty fish and shellfish components were used in the 2007 model, while 22 were used in the 2016 model. A significant increase in biomass was found in blue swimming crab, but biomass declined for other demersal fishes, cephalopods, and Penaeid shrimps. The production/biomass ratios of most components were higher in 2016 but the consumption/biomass ratios were relatively unchanged. The ecotrophic efficiency indicated that shellfishes were more exploited than fishes. Changes in most of the ecological indices revealed higher maturity and stability after 10 years of crab bank operation. The mixed trophic impact indicated bottom-up regulation, and that the increase of blue swimming crab negatively impacted only Mantis shrimp. Overall, the results indicate positive impacts of the crab bank intervention. [ABSTRACT FROM AUTHOR]

The livelihood of crab collecting, practised for generations in the Sundarbans forest of India, has undergone a radical moral makeover in recent years. Largely landless crab fishers are now the subject of frequent public denunciations by local authorities for their supposed greed and reckless endangerment of the entire ecosystem. While greed and its related category of need emerge from a local moral ecology of the region, internationally funded conservation campaigns and recent disruptions in the global crab supply chain reveal how accusations are activated and the means through which they play out amidst pre‐existing village hierarchies. This article accounts for the political, economic, and moral shifts that underpin these accusations. In counterpoint, I present the defences of the accused, and explore crab collectors' notions of a sufficient life and the rich moral distinctions they themselves make between greed (lobh), need (aubhav), desire (chahida), and habit (swabhav). I then step back to show the broader political contours that shape the discourse of 'greedy' crab collectors. I argue that both the conservation movement and allied state actors have distorted the material and moral resources intended to combat climate change and other environmental threats by scapegoating the politically disenfranchised: local fishers. Powerful stakeholders, as a result of their own political impotency, are deployed in a game of crab antics that fails to address the underlying environmental catastrophe while displacing the psychic burden of greed onto the poor. [ABSTRACT FROM AUTHOR]

Abstract The Jonah crab, Cancer borealis , supports a rapidly growing commercial fishery in southern New England. However, a lack of data concerning its life history, including growth dynamics, hinders the creation of a thorough stock assessment for the species. In this study, the incremental growth and seasonality of molting in Jonah crabs from Rhode Island Sound was examined in specimens collected from commercial traps and monitored in flow-through seawater tanks. Regression analysis from molt increments of 119 female and 91 male crabs indicated growth dimorphism in mature Jonah crabs, with diverging trends in proportional growth with size between the sexes at the sizes observed. Molting seasonality and size-dependent molt probabilities in male Jonah crabs were studied via periodic sampling and observation of male specimens in a laboratory setting across a range of 10-mm carapace width size bins throughout a year-long period. Laboratory results were corroborated by seasonal patterns in shell disease and molting conditions recorded while sampling at sea in Rhode Island Sound during commercial fishing operations. A discrete molting season was identified in June for male Jonah crabs smaller than 120 mm. Molting probability decreased with increasing carapace width and males larger than 120 mm did not molt during the year-long study, suggesting that growth is slow and molting events are rare for C. borealis at larger sizes in this region, or that there are ontogenetic migrations in the species and molting occurring outside the study region. Results presented here provide fundamental growth information for C. borealis with direct implications for management of the Rhode Island Sound fishery. [ABSTRACT FROM AUTHOR]

The size at the onset of maturity of the blue crab (Portunus pelagicus) is an important reference for decision making in fisheries management. The size at 50% sexual maturity (SOM50) was investigated for crabs from the opposite coasts (east and west) of peninsular Malaysia. A total of 1554 and 1546 crabs from Kuala Kedah (west) and Mersing (east), respectively were utilized. Four common models were used for estimating SOM50. The SOM50 estimated for females (113-118 mm) were higher than males (105-110 mm). Crabs from Kuala Kedah attained maturity at bigger size than crabs from Mersing. The Akaike information criterion corrected for small sample indicated that the models were comparable but Lysack's model appeared the best for female crabs from Kuala Kedah. The use of gonadosomatic index (GSI) to estimate size at maturity for this species is not precise. [ABSTRACT FROM AUTHOR]

Fish are important for food supply, especially in developing countries. In Southeast Asia, including Myanmar, the mud crab fishery is an important livelihood that represents a valuable source of income and food to coastal communities. However, the increasing demand for mud crab in domestic and international markets and poor management has generated concern about the status of this fishery across Southeast Asia. In this region, at least four species of mud crab in the genus Scylla are recognised but their correct identification and occurrence remain to be fully explained. Relying on accurate taxonomic identification of mud crab species represents the cornerstone of the successful implementation of management plans as life history biology and relative exploitation rates may vary by species due to gear susceptibility. Toward this aim, tissue samples from mud crabs were collected from four fishing communities of the Mergui archipelago, in the Tanintharyi region of southern Myanmar. All crab samples were DNA barcoded for species identification through sequencing. This study is the first genetic characterization of the mud crab fishery in Myanmar and revealed that Scylla olivacea was the only species found in the sampled fisheries of the Tanintharyi region. The populations studied across the Mergui archipelago did not show evidence of genetic structure, but gene flow appeared to be limited among conspecifics from neighbouring countries. [ABSTRACT FROM AUTHOR]

Spatial distributions of fished species must be well characterized to avoid local depletions, identify critical habitat, and predict and mitigate interactions with other fisheries. The Bristol Bay red king crab (Paralithodes camtschaticus) fishery is one of the largest crab fisheries in Alaska. Summer crab distributions have been well documented by decades of bottom trawl surveys. However, crab movement and distribution are poorly understood outside the summer survey period, which creates several management challenges. One important component of fishery management is the existence of no-trawl zones, which are intended to protect crab from bottom trawl fisheries. However, it is difficult to evaluate the placement of no-trawl zones, because most crab bycatch occurs in trawl fisheries during winter when crab distributions are unknown. Daily fishing logs, kept by skippers in the red king crab fleet since 2005, contain detailed information on the spatial distribution of catch and effort of legal sized male crab during the autumn crab fishery. However, data contained in these hand-written logbooks have not been readily accessible. We digitized daily fishing logs from 2005 to 2016 and used spatial information on catch and effort to infer geographic distributions of legal sized male king crab during the crab fishing season. Changes in distribution were tracked across this 12-yr period and comparisons were made between warm and cold temperature regimes. In warm years (2005, 2014–2016), crab aggregated in the center of Bristol Bay, Alaska, while in cold years (2007–2013) they were closer to the Alaska Peninsula. The majority of crab were caught in no-trawl areas (63.4% on average), but variations occurred among years and with temperature regime (40.0–86.8% in no-trawl zones). As temperatures continue to shift in the Bering Sea, it will be important to continue monitoring crab distributions outside the summer survey period. [ABSTRACT FROM AUTHOR]

The delayed mortality rate of crab discarded during fishing operations can be under- or overestimated in laboratory holding experiments, given the unnatural conditions and the short-term duration of these experiments. To evaluate the extent to which a method affects accuracy in these estimations, we compared mortality rates established through laboratory holding with mortality inferred from a yearand- a-half long tag-return study of Dungeness crab (Cancer magister) discarded in Oregon crab fisheries. The reflex action mortality predictor (RAMP) approach, which relates reflex impairment to probability of mortality, was applied in both studies. Similar patterns in mortalityand tag return- rates with respect to fishery, sex, reflex impairment, shell hardness, and injury from the 2 studies lends support to the reliability of the laboratory-generated mortality rates. However, results suggest that mortality rates determined in captivity are likely underestimated when crab are dropped a distance of greater than 6 m (and potentially less) back to water. This underscores the importance of determining the contribution to mortality of variables in the capture, handling, and discard process that are not incorporated in a study to estimate mortality of discarded animals. Both studies also highlighted the significance of sample size when applying the RAMP approach to a fishery with low rates of discard mortality. [ABSTRACT FROM AUTHOR]

The fishing effort of a Sinaloa crab fishery in the Gulf of California in 2014 was analysed based on fishermen’s interviews, official catches and permits, and information from a sample of fishing logbooks from five fishery cooperatives operating in four coastal lagoons that contained the daily catch from individual fishing trips. Unauthorized gear, a double-ring net (DR), was used most frequently (>70% of the fishers) for crab fishing, although authorized single-ring nets and Chesapeake traps (CT) were also used with low frequency. The estimated fishing effort was 641 boats/day in the four coastal lagoons, which was 34% more than authorized, and 818 boats/day were employed in all of Sinaloa. A total of 57 479 fishing gears were estimated for the study area, which was 49.9% greater than the maximum authorized number, and 80 822 nominal fishing gears were estimated for the entire Sinaloa crab fishery, 14.15% more than the total gear limit (70 800). The size of the mesh used in the gear was smaller than the authorized limit of 76 mm, and >50% of the catches included crabs of unlawful size. It is argued that the effort must be regulated in terms of the number of vessels, per unit time, and not the number of gears. The information from this study demonstrates a failure to monitor compliance with current regulations and thus means that other strategies for the sustainable management of the fishery, such as co-management, should be tested. [ABSTRACT FROM AUTHOR]

Commercial exploration of swimming crab is rapidly increasing worldwide. In 2015, total production of crabs (fisheries plus aquaculture) reached almost 1300 thousand tons. One of the most valuable marketing forms is called 'soft-shell crab'. The internet is one of the most important marketing channels for soft-shell crab, with prices starting at US$3.5 a unit, but going up to US$8.00-10.00, depending on the size and presentation form of the product (live, cooled, frozen, or processed). In luxury restaurants, a dish containing one large animal may cost well over US$75.00. Increasingly, this market requires exporting companies to present some kind of quality certification of the product or process (mainly certifications related to food safety). Almost all soft-shell crab production is based on crabs caught in the wild, by either trawling or trapping. Crab populations are suffering from environmental impacts associated with human activity, so much that obtaining the raw material (crabs in pre-molt stage) has become the biggest challenge for companies that market soft-shell swimming crab nowadays. Even recognizing the aquaculture as an alternate form to acquire crabs, it is necessary to understand that technology for commercial crab cultivation is still incipient and restricted to some species of few genera, such as Scylla, Portunus, and Callinectes. The present article reviews and discusses the problems and challenges related to the productive chain of soft-shell swimming crab, and presents an overview of the worldwide market, identifying the main exporting and importing centers, and their respective trading methods. [ABSTRACT FROM AUTHOR]

The Hawke Box is an offshore area (8610 km2) of the boreal Northwest Atlantic that at the request of local fishers was closed to trawling and gillnetting in 2003, but remained open to seasonal snow crab ( Chionocetes opilio) pot fishing. Closure was a precautionary management measure primarily to sustain the crab fishery and secondarily to conserve cod known to aggregate there. Fall (1996-2013) and spring (1996-2003, 2015) surveys indicated that biological community assemblages changed significantly before-after and inside-outside the closure (PERMANOVA P < 0.01). Crab fishery data (1996-2013) indicated that landings and relative production declined throughout the region after closure, but was significantly more outside than inside. Atlantic cod ( Gadus morhua) increased inside and outside the closure, and several other demersal species increased significantly more inside. The Hawke Box provides a unique boreal area for the study of restrictions on trawling and gillnetting in an area with historically strong fisheries, restrictions that are strongly supported by local fishers. The overall evidence suggests that within a decade the Hawke Box has benefited fisheries communities, fisheries production, and biodiversity conservation. [ABSTRACT FROM AUTHOR]

We found that crab discarded from Oregon (USA) commercial and recreational fisheries for Dungeness crab ( Cancer magister) have lower postrelease mortality than previously estimated. This aligns with the goals of the '3-S' management strategy currently employed for these fisheries, to protect discarded sublegal male (Size), female (Sex), and soft-shell (Season) crab. We found that for the commercial ocean Dungeness fishery, overall discard mortality rates (5 days after release) were 0.080 (95% confidence interval: 0.061-0.100) for females; 0.012 (95% confidence interval: 0.002-0.022) for hard-shell males; and 0.092 (95% confidence interval: 0.026-0.157) for soft-shell males. The overall discard mortality rate for the recreational bay fishery (from a boat) was estimated to be 0.009 (95% confidence interval: 0-0.018). A reflex action mortality predictor relationship, which relates reflex impairment to mortality probability, was created and utilized to estimate mortality rates. Our study highlights the importance of looking not only at discard and mortality rates to evaluate 3-S fishery management, but also the mortality- and bycatch-per-retained ratios and temporal trends relative to changes in effort, animal condition, and catch composition. [ABSTRACT FROM AUTHOR]

The effects of antibiotics on the external deformities, growth and survival of mud crab Scylla serrata larvae and juveniles were determined. Zoeae were exposed to oxytetracycline ( OTC) (0, 3.0, 6.0, 9.0, 12 mg L−1) and furazolidone ( FZD) (0, 0.5, 1.0, 1.5, 2.0 mg L−1) in the first and second experiments, respectively, until the late megalopa. The crab instars were grown in nursery tanks for 1 month. Larvae survived until megalopa only at 3.0 and 6.0 mg L−1 OTC or 0.5 and 1.0 mg L−1 FZD. These four concentrations were run simultaneously in another experiment. Morphological deformities in zoea 5 were bent dorsal, rostral and furcal spines. There was no significant difference ( P > 0.05) on the deformities of zoea 5 in 3.0 and 6.0 mg L−1 OTC and 0.5 and 1.0 mg L−1 FZD. Significantly ( P < 0.05) higher survival and faster growth were attained in 3.0 mg L−1 OTC and 0.5 mg L−1 FZD. Deformities observed in juveniles were fused frontal and lateral spines, asymmetrical and depressed tip of abdominal flap and gap between sternites. High percentage occurrence of deformities was observed in the 6.0 mg L−1 OTC and 1.0 mg L−1 FZD in the first and third experiments, respectively. There was no significant difference ( P > 0.05) observed in the survival of juveniles in OTC and FZD treatments. However, growth was significantly ( P < 0.05) faster in lower concentrations of the two antibiotics. The study shows the effects of OTC and FZD in the morphology of mud crab. Therefore, there is a need to eliminate the use of antibiotics and find alternatives. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The diamondback terrapin ( Malaclemys terrapin ) is endemic to marshes, coves, and tidal creeks on the Atlantic and Gulf coasts of the United States. Currently, the terrapin is listed as a species of special concern in several states where one of the prominent threats to populations is the drowning of terrapins in commercial crab pots. Bycatch reduction devices (BRDs) that narrow the funnel opening on crab pots exclude terrapins, but BRDs face opposition from the fishing industry due to fears that they will decrease target species catch. The primary goals of this research were to examine the efficacy of two sizes of BRDs in excluding terrapins from crab pots and to assess the impact of BRDs on blue crab catch. Crab pots were deployed in paired and triplicate designs at estuarine sites along the central and southern coast of North Carolina in the summers of 2012 and 2013. A total of 4039 legal sized blue crabs and 14 terrapins were captured over the course of the study. Bycatch reduction devices did not have a statistically significant effect on catch rates or carapace width of legal-sized blue crabs. Thirteen of the 14 captured terrapins were in control pots, and one male terrapin was captured in a pot equipped with a large size BRD. An integrated approach that combines data on the spatial ecology and demography of terrapins with information on the most appropriate BRD dimensions for terrapin exclusion is most likely to succeed in addressing the issue of terrapin bycatch. [ABSTRACT FROM AUTHOR]

Owing to the influence of the Humboldt Current many cold-water adapted brachyuran crabs of commercial interest have vast (>40°latitude) distributional ranges along the Pacific Coasts of Peru and Chile. Development of artisanal diving and trapping fisheries on these crabs (mainly Cancridae and Xanthidae) is either uncontrolled (Peru) or existing management measures, like the minimum landing size of 12 cm carapace width, and the prohibition to catch ovigerous females, are poorly enforced (Chile). Under El Niño conditions, occurring on average every 4 years, the upper temperature limit of these temperate species can be exceeded in Peru, leading to mass mortalities of adult crabs and a breakdown of the artisanal crab fishery. Temperature changes (latitudinal or in the course of El Niño Southern Oscillation) may have pervasive effects on reproduction and early life history stages as represented for Romaleon setosus, which ultimately determine the recruitment of crabs to the fishery. The recent development of the fishery, namely the decline of the landings of Romaleon setosu s and Homalaspis plana in Central- to Northern Chile, compensated by the rapidly developing fishery on Metacarcinus edwardsii in Southern Chile is presented and discussed in the light of temperature effects on the crabs’ (reproductive) biology. We conclude that an enforcement of the legal minimum size is needed to allow for a sustainable fishery of both species throughout their distribution range. [ABSTRACT FROM AUTHOR]

Octopus maya is a major socio-economic resource from the Yucatán Peninsula in Mexico. In this study we report for the first time the chemical composition of the saliva of O. maya and its effect on natural prey, i.e. the blue crab (Callinectes sapidus), the crown conch snail (Melongena corona bispinosa), as well as conspecifics. Salivary posterior glands were collected from octopus caught by local fishers and extracted with water; this extract paralyzed and predigested crabs when it was injected into the third pereiopod. The water extract was fractionated by membrane ultrafiltration with a molecular weight cut-off of 3kDa leading to a metabolic phase (>3kDa) and a neurotoxic fraction (<3kDa). The neurotoxic fraction injected in the crabs caused paralysis and postural changes. Crabs recovered to their initial condition within two hours, which suggests that the effects of the neurotoxic fraction were reversible. The neurotoxic fraction was also active on O. maya conspecifics, partly paralyzing and sedating them; this suggests that octopus saliva might be used among conspecifics for defense and for reduction of competition. Bioguided separation of the neurotoxic fraction by chromatography led to a paralysis fraction and a relaxing fraction. The paralyzing activity of the saliva was exerted by amino acids, while the relaxing activity was due to the presence of serotonin. Prey-handling studies revealed that O. maya punctures the eye or arthrodial membrane when predating blue crabs and uses the radula to bore through crown conch shells; these differing strategies may help O. maya to reduce the time needed to handle its prey. [ABSTRACT FROM AUTHOR]

Demographic models of pre- and post-recruitment population dynamics were developed to account for the effects of ocean acidification on biological parameters that affect southern Tanner crab (Chionoecetes bairdi) larval hatching success and larval and juvenile survival. Projections of stock biomass based on these linked models were used to calculate biological and economic reference points on which fisheries management advice is based and thus provide fisheries managers with strategic advice on the likely long-term consequences of ocean acidification. The models utilized information for southern Tanner crab in the eastern Bering Sea. This information included the monitoring data on which conventional size-structured stock assessments are based, as well as the functional relationships that determine survival based on experiments that evaluated the consequences of ocean acidification over the next 100-200 years on crab larval hatching success, larval survival, and the survival of juvenile crab. The results highlighted that juvenile survival had the largest effect (~20% decrease over 75 years) on biological and economic reference points, while hatching success, particularly if density dependence occurs after hatching, and larval survival have smaller effects (<10% decrease). Catch and profits would be expected to decrease by >50% in 20 years if natural mortality is affected by ocean acidification. Additional laboratory data on oocyte and embryo development leads to large changes in biological reference points depending on the timing of ocean acidification effects relative to natural mortality. The results highlight the need for experiments to evaluate the longer term physiological effects of ocean acidification on multiple life history stages and to measure indices that directly inform population dynamics models to evaluate future management scenarios. [ABSTRACT FROM AUTHOR]

Aquaculture is an important source of atmospheric methane (CH4) K and nitrous oxide (N2O), while few direct flux measurements are available for their regional and global source strength estimates. A parallel field experiment was performed to measure annual CH4 and N2O fluxes from rice paddies and rice paddy converted inland crab--fish aquaculture wetlands in southeast China. Besides N2O fluxes dependent on water/sediment mineral N and CH4 fluxes related to water chemical oxygen demand, both CH4 and N2O fluxes from aquaculture were related to water/sediment temperature, sediment dissolved organic carbon, and water dissolved oxygen concentration. Annual CH4 and N2O fluxes from inland aquaculture averaged 0.37 mg m-2 h-1 and 48.1 µg m-2 h-1, yielding 32.57 kg ha-1 and 2.69 kg N2O--N ha-1, respectively. The conversion of rice paddies to aquaculture significantly reduced CH4 and N2O emissions by 48% and 56%, respectively. The emission factor for N2O was estimated to be 0.66% of total N input in the feed or 1.64 g N2O --N kg-1 aquaculture production in aquaculture. The conversion of rice paddies to inland aquaculture would benefit for reconciling greenhouse gas mitigation and agricultural income increase as far as global warming potentials and net ecosystem economic profits are of concomitant concern. Some agricultural practices such as better aeration and feeding, and fallow season dredging would help to lower CH4 and N2O emissions from inland aquaculture. More field measurements from inland aquaculture are highly needed to gain an insight into national and global accounting of CH4 and N2O emissions. [ABSTRACT FROM AUTHOR]

The intergenerational continuity of fishing communities is a growing concern for the sustainability of small-scale fisheries around Europe. This is exemplified through the case of an English crab fishery where young people are being encouraged into fishing through funded training programmes with limited success. Opportunities for work have declined, most notably through a reduction in crew size to save costs. Interviews with fishermen of different ages are explored using access theory to elucidate how the social reproduction of fishing has changed. This shows how the agency of young aspiring fishermen is increasingly constrained by regulatory and financial factors. Improved social and spatial mobility among fishing families mean that recruitment into the fishery through a father-to-son pathway is increasingly uncommon. Youngsters from non-fishing families face additional financial and relational barriers. Funded courses alone cannot provide a solution. A holistic approach to rural coastal development is required to build social resilience in fishing communities across Europe faced with similar problems. [ABSTRACT FROM AUTHOR]

The prevalence of disease in edible crabs ( Cancer pagurus ) was assessed at two sites in South West Wales; one estuarine (Pembroke Ferry) and another facing open water (Freshwater East). Diseases included pink crab disease caused by Hematodinium sp., an infection of the antennal gland caused by Paramikrocytos canceri and an idiopathic inflammatory condition of the connective tissue surrounding the anterior ganglionic masses. This latter condition was only found in crabs from Pembroke Ferry. There was a significantly higher prevalence of pink crab disease at Freshwater East than Pembroke Ferry, although both sites had similar levels of infection by P . canceri . [ABSTRACT FROM AUTHOR]

Sperm depletion in males can occur when polygynous species are intensively exploited under a male-biased management strategy. In fisheries involving crabs species, the effects of this type of management on the reproductive potential is far from being understood. This study tests whether male-biased management of the principal Chilean crab fishery is able to affect the potential capacity of Metacarcinus edwardsii males to transfer sperm to females. Five localities in southern Chile, recording contrasting crab fishery landing, were selected to assess the potential of sperm depletion triggered by fishery. Seasonally, male crabs from each locality were obtained. Dry weight and histological condition of vasa deferentia and the Vaso-Somatic Index (VSI) were determined in order to use them as proxies for sperm depletion and male reproductive condition. A manipulative experiment was performed in the laboratory to estimate vasa deferentia weight and VSI from just-mated males in order to obtain a reference point for the potential effects of the fishery on sperm reserves. Sperm storage capacity is significantly affected by fisheries; during the mating season vasa deferentia from localities with low fishery intensity were heavier than those from high intensity fisheries, and these differences were even more evident in large males. Histological section showed that this disparity in vasa deferentia weight was explained principally by differences in the quantity of spermatophores rather than other seminal material. VSI was always higher in males from localities with low fishery intensity. Males from localities with high fishery intensity showed little capacity to recover sperm reserves and the VSI of these males remained below the values of the just-mated males. Detriment in the capacity of males to transfer sperm is the first step to sperm limitation in an exploited population, thus detection of sperm depletion can be an alert to introduce changes in the current management of crabs. [ABSTRACT FROM AUTHOR]

Highlights: [•] B MSY estimates are needed to manage Alaska crab fisheries. [•] Proxy methods for estimating B MSY are currently used for management. [•] Methods which use stock and recruitment data and allow for changes in productivity due to the environment are outlined. [ABSTRACT FROM AUTHOR]

Small-scale mud crab aquaculture was introduced in East Africa in late 1990s as a mangrove friendly aquaculture to improve the livelihood of coastal communities through organised community groups (OCGs). The OCGs approach was a strategy aimed at ensuring benefits to the village and regulating access to the open access resource (land in mangrove forests). A social and economic assessment was conducted at Majaoni, Makongeni, Ihaleni and Dabaso along the Kenyan coast. The paper looks at the social and economic characteristics of the groups, their management systems, contribution of mud crab aquaculture to the livelihoods of local communities and policy issues related to the interventions. There is wider involvement of the mijikenda community in mud crab farming; however, the level of women participation is low. A strong market link exists between the groups and the different market outlets, where hotels and exporters offer the highest prices. Regional price variations existed and may need networking between the groups. The paper concludes that national policies may need to be redirected to support small-scale aquaculture development and ensuring capacity building for women, operation and management of groups, provision of extension services, data management and provision of user rights for communities working in the mangrove environment. [ABSTRACT FROM AUTHOR]

The fisheries for crabs and lobsters (Reptantia, Decapoda) are shaped by environmental variation through the distribution ecology, productivity or even their market traits such as colour and size. Many crabs and lobsters have a wide latitudinal distribution and therefore are exposed to significant abiotic gradients throughout their geographic range. Environmental factors affect reptantians throughout their complex life cycle, including embryo development, timing and length of the spawning period, the duration and quality of the larval stages, the level and spatial distribution of the settlement, growth rates and size of the juveniles, size at maturity, and catchability. The most consistent environmental response is of growth and reproduction to temperature. Growth rates increase with increasing temperatures in a parabolic function, tapering and then declining as the boundaries of thermal tolerance are reached. With increasing temperature the intermoult duration decreases. Once the upper thermal boundary is reached, increases in temperature result in longer intermoult duration and smaller growth increments so that growth is reduced. Declines in temperature generally suppress moulting, and consequently reptantians rarely moult in winter. Increasing temperature decreases the time for egg incubation, larval development and the maturational age. Catchability increases with water temperature and also varies, although less predictably, with moon phase and wind strength. Catchability decreases with an increase in population density. Larval settlement of many reptantian species depends on current strength, increasing with the strength of certain local currents. Reptantians can tolerate a wide-variety of conditions and have flexible life-histories to respond to conditions throughout their broad geographic ranges. Information on environmental effects on reptantians not only assists in understanding probable effects of ocean warming and acidification, but also seasonal and interannual changes in fisheries production. [ABSTRACT FROM AUTHOR]

Malaclemys terrapin terrapin (Northern Diamondback Terrapin) is susceptible to drowning in commercial-style pots used for the Callinectes sapidus (Blue Crab) fishery. Regulations to reduce by-catch mortality vary by state. We compared three different regulatory strategies with respect to crab catch and their relative effectiveness at reducing terrapin by-catch. To mimic their possible use by recreational crabbers, we grouped and fished together ten unbaited crab pots with no by-catch reduction devices (BRDs), ten with large BRDs, and ten with small BRDs in a tidal creek in southeastern Virginia. Over 24 sampling days, the total legal crab catch (crabs ≥ 12.7 cm) in pots with no BRDs (29.9 ± 10.0 SD crabs pot-1) and large BRDs (27.9 ± 6.2 crabs pot-1) was significantly greater than catch in pots with small BRDs (14.0 ± 5.8 crabs pot-1). Legal crabs varied in average size from 14.1 ± 1.2 cm, 14.0 ± 1.2 cm, and 13.7 ± 1.0 cm from pots with no BRDs, large BRDs, and small BRDs, respectively, but these differences were not significant. Of a by-catch of 71 terrapins, 69 were from pots with no BRDs, 2 from pots with large BRDs, and none from pots with small BRDs. The potential mortality of terrapins in pots without BRDs would have reduced the population in this tidal creek by 42% in just 24 days. Based on these results, regulations requiring the use of large BRDs come closest to the objective of reducing by-catch mortality of terrapins without a large effect on crab capture in Virginia. Both recreational crabbing and commercial crabbing with no BRDs on pots in terrapin habitat can contribute to declines in local terrapin populations. [ABSTRACT FROM AUTHOR]

Abstract: Parasites can significantly impact ecosystems by altering the distributions and population sizes of their host organisms. Some hosts are thought to find refuge from parasitism by entering habitats where their parasites cannot survive. The nemertean worm Carcinonemertes errans is an egg predator that infects the Dungeness crab, Cancer magister, throughout the host's range. To determine if C. magister experiences a refuge from C. errans within estuarine environments, we examined the distribution of C. errans on Dungeness crabs within Oregon's Coos Bay Estuary. Year-round sampling over a three-year period also allowed us to test for temporal variation in the parasite's distribution. We found that parasite prevalence, mean intensity, and parasite density of C. errans infecting C. magister varied along a clear estuarine gradient, with crabs nearest the ocean carrying the heaviest parasite loads. Larger crabs were more heavily infected with worms, and seasonal infection patterns were observed at some sites within the bay. Crabs sampled from coastal waters near the estuary carried significantly more worms than did crabs from the bay, suggesting that the estuary is acting as a spatiotemporal parasite refuge for this important fishery species. [Copyright &y& Elsevier]

The Sustainable TEchnologies for LittoraL Aquaculture and MArine REsearch (STELLA MARE) platform has as an objective to provide data for the management of the sea in relation with the fishing industry. In this paper, we introduce the first experiment on the active tracking of a crab species, Maja squinado, symbolic of the deregulation of fishing activity. This paper introduces the method used for monitoring Maja squinado and the first collected data on the behavior of this little-known species. [ABSTRACT FROM AUTHOR]

Highlights: [•] The swimming crab P. trituberculatus is the world's largest crab fishery. [•] AFLP population genetics analyses were conducted among its main fishing areas. [•] Genetic diversity appears high in populations from its three main fishing areas. [•] Genetic differentiation occurs among populations from its three main fishing areas. [•] A genome-wide signal of population genetic differentiation was detected. [ABSTRACT FROM AUTHOR]

Abstract: Many crab fisheries target large males, which can cause their densities to differ greatly in areas where they are fished and areas where they are protected, such as inside marine reserves. The size and gender of crabs potentially affect their ability to compete for resources, with competition likely to favour larger male crabs, raising the potential for cascading effects on females or smaller crabs in reserves. The role of size and gender in structuring the outcomes of competitive interference interactions between mud crabs (Scylla serrata Forskal) was tested by placing crabs in tanks with a competitor of smaller, equal or greater size, and of the same or differing gender. The behaviour of crabs was recorded for 15min, and the times spent feeding, attacking, threatening and avoiding were compared among the different size and gender combinations. Male and female crabs spent less time feeding and more time avoiding in the presence of larger male than larger female crabs. Female crabs spent more time avoiding male crabs of equal size than female crabs of equal size. Male crabs of equal size spent the most time attacking. The size and gender-dependent responses of mud crabs to competition may lead to quite unexpected effects inside marine reserves. [Copyright &y& Elsevier]

Sethi, S. A., Dalton, M., and Hilborn, R. 2012. Managing harvest risk with catch-pooling cooperatives – ICES Journal of Marine Science, 69: 1038–1044.Catch-pooling cooperatives are a strategy for fishers to manage variability which can be organized independently of a central management agency. We examined the statistical properties of equal-share catch-pooling cooperatives, and tested their potential to mitigate risk using data from two Bering Sea crab fisheries prior to rationalization. The results suggest that small cooperatives of crabbers could have reduced vessel-level catch risk by as much as 40% in the red king crab fishery, but would have been ineffective in the snow crab fishery. Analytical examination of catch variances under cooperatives explains the discrepancy between the two fisheries and demonstrates that variability reduction depends on the degree of correlation amongst participants' catches. In the best-case scenario, catch-pooling cooperatives can diversify away all season to season variation resulting from individuals' luck and skill, leaving only variation in fishery-wide harvest. [ABSTRACT FROM PUBLISHER]

Abstract: From a historical perspective, several protistan taxa, including the recently re-aligned Microsporidia, have been associated with or identified as causes of mortalities in crustacean populations. Depending upon the host species, associated protistan prevalences could be as low as 5% or approach 100%. It has generally been assumed that reported prevalences translated directly into significant mortalities that could impact the distribution and abundance of affected populations. However, this assumption may be incorrect especially when the dynamics of host–pathogen–environment interactions are not entirely understood. We will discuss the presumed impact of several protistan pathogens on temperate and cold water commercial crab species. By using selected examples such as a ciliate in the Dungeness crab (Cancer magister) and Hematodinium sp. infections in North Pacific crabs, we will attempt to contrast differences between prevalence and mortality, acute and chronic infections/mortalities, age or size selectivity of affected population, and geographically restricted and widespread epizootics. We will also briefly discuss the potential impact of environmental changes such as climate change and ocean acidification on both host and protistan pathogen. [Copyright &y& Elsevier]

ABSTRACT. Crustaceans worldwide are infected with alveolate parasites of the genus Hematodinium, causing substantial losses to langoustine and crab fisheries. The distinct seasonality in Hematodinium occurrence in their decapod hosts, as well as unsuccessful attempts at transmission, suggest the existence of life stages outside their benthic crustacean hosts. We used a nested polymerase chain reaction method to detect Hematodinium rDNA in the environment and in potential alternative hosts. Environmental samples from the Clyde Sea, Scotland, were screened during the April release of dinospores and during June and August, when infection prevalence is rare in benthic crustaceans. Hematodinium rDNA was amplified in 15% (14/94) of isolated langoustine larvae, and in 12% (13/111) of crab larvae. In addition, Hematodinium rDNA was present in mixed plankton samples devoid of decapod larvae, but including the 2 μm-10 mm fraction of particulate organic matter in the water column, containing phytoplankton and other zooplankton. These results indicate that Hematodinium occurs in the water column and is harboured by planktonic organisms, including larval stages of the crustacean hosts, when infections are at their lowest in adult hosts. [ABSTRACT FROM AUTHOR]

The shore crab Carcinus maenas is a commercially important species, utilised as sea angling bait as well as supporting a European-wide fishery. Hatchery production could provide an alternative source of bait crabs, alleviating potential competition between these sectors and environmental concerns regarding bait collection practices. A series of experiments were carried to investigate the potential for hatchery production, focusing on effects of dietary regimes and stocking densities through the zoeal stages and the influence of tank substrates and stocking density during the megalopa stage. Inclusion of the rotifer Brachionus plicatilis as live food for early larval stages conveyed no advantage in terms of survival or rate of development compared to a diet of Artemia nauplii. Increasing zoea stocking densities (from 94 to 557 l) had a significantly negative effect upon survival to the megalopa stage (from 75% down to 47%), although this was off-set by a significant increase in production, with 260 megalopae produced from an initial density of 557 zoeae l. The inclusion of substrates for megalopa stages had no impact on production or development rate, compared to tanks with no substrate. The completely benthic behaviour of megalopae indicates that tank floor area will be a limiting factor for crab production. Increasing stocking density of megalopae was found to significantly and negatively influence survival, although above 10,000 megalopae m the rate of decline in survival stabilised and maximum production (3,114 juveniles m) of juvenile crabs could be achieved at the highest stocking densities tested (40,000 m). [ABSTRACT FROM AUTHOR]

The juvenile Chinese mitten crabs Eriocheir sinensis (1.40 ± 0.43 g) were cultured in water of 5.34 ± 0.43 (hypoxia, treatment group) and 21.02 ± 0.06 kPa (high dissolved oxygen (DO), control group) DO for 24 h, respectively. The total hemocyte counts (THC), the hyaline hemocyte counts were measured at 0 and 24 h in the treatment group, and superoxide dismutase (SOD) activity, concentrations of lactic acid and hemocyanin (Hc) in hemolymph and the metabolism of hepatopancreas (concentrations of glucose, total cholesterol, uric acid, total protein, urea, triglyceride in hepatopancreas) were assayed at 0, 2, 8, and 24 h in both treatment and control groups. The hyaline hemocyte counts and THC decreased significantly by 66 and 49% after exposure to hypoxic water for 24 h, respectively. SOD activity, Hc and lactic acid content were significantly affected in treatment group, and there were significant differences between treatment and control groups. In the treatment group, the concentration of glucose, cholesterol and uric acid in hepatopancreas had a significant variation for 24 h. The concentration of total protein, urea and triglyceride between treatment and control groups was not significantly different after 0, 2, 8, 24 h. However, there were significant differences between treatment and control groups in terms of total protein, glucose, and uric acid concentration. Taken together, the effect of hypoxia is comprehensive in juvenile Chinese mitten crab Eriocheir sinensis. [ABSTRACT FROM AUTHOR]

Abstract: Laying artificial materials on the shore to create refugia that attract crustaceans is a ‘fishing’ technique known mainly from South America and the UK. In the UK, this method of fishing is known as ‘crab-tiling’, which involves laying of roof tiles, pieces of guttering or car tyres (‘crab-tiles’) intertidally in estuaries to provide habitat for Carcinus maenas. Crabs are then harvested for use as angling bait. C. maenas are known to reside under crab-tiles during low tide, however the extent to which crab-tiles influence the distribution and behaviour of crabs and other estuarine fauna during high tide is not clear. To investigate this, fixed underwater video cameras were deployed on a mudflat over two separate occasions in control (non-tiled) and tiled sites. Crabs were significantly more abundant in crab-tiled sites than control sites, and they remained relatively stationary, travelling less in tiled sites than those in control sites. The abundance of mobile fauna (e.g. benthic gobies, mysids, crabs and pelagic fishes) was greater in control sites than in tiled sites during July. The same trend was observed in March but was not significant. Diversity (number of taxa) tended to be greater in control sites than tiled sites on both occasions, but the trend was not significant. The faunal assemblage was not different between control and tiled treatments in either March or July. Crabs occupied crab-tiles throughout high tide immersion, and qualitative observations indicated a tendency to aggressively defend particular tiles. It also seems likely that the tiles provided some protection for the crabs from fish and diving birds. [Copyright &y& Elsevier]

Dvoretsky, A. G., and Dvoretsky, V. G. 2010. Epifauna associated with an introduced crab in the Barents Sea: a 5-year study. – ICES Journal of Marine Science, 67: 204–214.Species composition, prevalence, intensity, and spatial distribution of macro-invertebrates colonizing the invasive red king crab (Paralithodes camtschaticus) in a typical bay of the Barents Sea, Dalnezelenetskaya Bay (depths 5–40 m), and adjacent deeper water (120–180 m) were examined in the summers of 2004–2008. In all, 43 associated species were found on the crabs. The most common epibionts were Mytilus edulis (Bivalvia), Obelia spp. (Hydrozoa), and Circeis armoricana (Polychaeta). Symbiotic species included Ischyrocerus commensalis and Ischyrocerus anguipes (Amphipoda), Harmothoe imbricata (Polychaeta), and Johanssonia arctica (Hirudinea). There were no significant differences in the prevalence of infestation between male and female crabs. The prevalence of most of the common species was greater in crabs with old shells than in crabs with new shells. Infestation levels of J. arctica were higher in deeper than in shallow water, and M. edulis was less abundant in deep water. All species found on the crabs appear to be native to the Barents Sea. However, I. commensalis amphipods were not found at the site examined before the introduction of the red king crab, indicating that their distribution may have changed after association with this host species. Introduced hosts may well influence the distribution of rare native species. [ABSTRACT FROM PUBLISHER]

Abstract: This study investigates the potential for using data from a vessel monitoring system (VMS) to create indices of commercial fishery performance that may be used in monitoring snow crab resource status. Fishing hours were screened from hourly positional signals to create an index of fishing effort (hours fished) for comparison with that derived from logbooks (number of trap hauls). Similarly, a VMS-based fishing catch per unit of effort (CPUE) index was developed for comparison with CPUE derived from logbooks. Analysis of these indices showed that VMS-based fishing effort and CPUE indices can be interpreted to provide reliable complementary or alternative indices to logbooks for assessment of fishery performance in the Newfoundland and Labrador (NL) snow crab (Chionoecetes opilio) fishery. We also developed a VMS-based index of fishing efficiency and illustrate how it can be applied toward understanding various behaviors and anomalies in the fishery. VMS data may offer other potential applications for snow crab assessment and management. Our approach and methods are applicable to other commercial fishery resources worldwide that are monitored using vessel monitoring systems. [Copyright &y& Elsevier]

The article presents a study which provides information on the discovered offshore areas of female blue crabs that are vulnerable to fishery exploitation and sand-mining disturbance. It examines the use of the Ship, Trinity, Tiger Shoal Complex (STTSC), as evidence for spawning , hatching, and foraging of blue crabs, through the analyses of condition factor, reproductive condition, and abundance. Moreover, it also examines the implications of the ecology, sand mining, and fishery management.

Variations in catch per unit effort (CPUE), distributions of size-structure, sex ratio, and spawning female conditions from a fishery were examined to better understand the impact of fishing activities. We collected data from crab fishery, which is a small-scale fishery in Chonburi, an eastern province of Thailand, during October 2006 - September 2007. Both CPUE and size-structure of the swimming crab varied seasonally. Sex ratio from the catch was not 1:1 and the distributions of both male and female varied by season. Even though it is premature to conclude that the stock is overfished, more management measures are recommended to prevent overfishing due to the concern of high proportion of females and the presence of numbers of spawning females in the catches. [ABSTRACT FROM AUTHOR]

The unusual goneplacoid crab, Vultocinus anfractus Ng & Manuel-Santos, 2007, the only member of the family Vultocinidae, is recorded from New Caledonia for the first time. The species, previously known only on the basis of males from the Philippines and Vanuatu, is now also represented by females. The female characters of the species are described and intraspecific variation is discussed. [ABSTRACT FROM AUTHOR]

Laboratory experiments were firstly conducted to determine the possibility of modification of the collapsible pot for blue swimming crab Portunus pelagicus by designing appropriate escape vents in terms of shape, position, and size to improve size selectivity by reducing the catch of immature crabs. In laboratory observations, nearly square-shaped vents of 35 mm height and 45 mm length, located at the lower part of the side panel, showed the best performance to allow the escape of immature-size crabs by side-crawling escape behavior through the vents, with L 50% selection carapace length (CL) of 39.1, 44.4, and 48.7 mm CL for 40, 45, and 50 mm vent length, respectively. Comparative fishing trials between conventional and vented pots with vents of 35 × 45 mm size were conducted to examine the crab size and species selectivity. Use of the vented pots was found to reduce the number of immature crabs in the catch from 70.5% to 11.0% on average, while not affecting the catch efficiency of mature-size crabs. The vented pots also had a selective effect for reducing the catch of bycatch species in comparative fishing trials. [ABSTRACT FROM AUTHOR]

Stentiford, G. D. 2008. Diseases of the European edible crab (Cancer pagurus): a review. – ICES Journal of Marine Science, 65: 1578–1592.The edible crab (Cancer pagurus) supports an important fishery in European waters. The fishery is increasing in size and in relative importance as stocks of marine finfish decline. Despite its importance, though, studies on the pathogens and parasites of this crab species are relatively lacking compared with studies of commercially exploited finfish and molluscan hosts. Recent basic surveys of C. pagurus stocks from the English Channel carried out by the Cefas laboratory at Weymouth have identified a new viral infection (C. pagurus bacilliform virus, CpBV) in juvenile crabs, and several new species of protistan parasite (Hematodinium sp., Paramarteilia canceri, and Enterospora canceri) in the adult population. The histopathology and prevalence of each of these pathogens suggests that each can induce host mortality and, further, that specific pathogens are differentially prevalent in juvenile and adult cohorts from similar geographic locations and at different times of the year. In this review, these newly discovered pathogens are placed in context with previously described bacterial, fungal, protistan, and metazoan pathogens of C. pagurus, and the potential for these pathogens to impact on the health of individuals and populations within the English Channel fishery is discussed. [ABSTRACT FROM PUBLISHER]

Abstract: Collection of marine invertebrates for use as fishing bait is a substantial activity in many parts of the world, often with unknown ecological consequences. As new fisheries develop, it is critical for environmental managers to have high quality ecological information regarding the potential impacts, in order to develop sound management strategies. Crab-tiling is a largely unregulated and un-researched fishery, which operates commercially in the south-west UK. The target species is the green crab Carcinus maenas. Those crabs which are pre-ecdysis and have a carapace width greater than 40 mm are collected to be sold to recreational anglers as bait. Collection involves laying artificial structures on intertidal sandflats and mudflats in estuaries. Crabs use these structures as refugia and are collected during low tide. However, the effect that this fishery has on populations of C. maenas is not known. The impact of crab-tiling on C. maenas population structure was determined by sampling crabs from tiled estuaries and non-tiled estuaries using baited drop-nets. A spatially and temporarily replicated, balanced design was used to compare crab abundance, sizes and sex ratios between estuaries. Typically, fisheries are associated with a reduction in the abundance of the target species. Crab-tiling, however, significantly increased C. maenas abundance. This was thought to be a result of the extra habitat in tiled estuaries, which probably provides protection from natural predators, such as birds and fish. Although crabs were more abundant in tiled estuaries than non-tiled estuaries, the overall percentage of reproductively active crabs in non-tiled estuaries was greater than in tiled estuaries. As with most exploited fisheries stocks, crabs in exploited (tiled) estuaries tended to be smaller, with a modal carapace width of 20–29 mm rather than 30–39 mm in non-tiled estuaries. The sex ratio of crabs however; was not significantly different between tiled and non-tiled estuaries. These results illustrate the potential to manage fished populations using habitat provision to mitigate the effects of fishing pressure. [Copyright &y& Elsevier]

Wahle, R. A., Bergeron, C. E., Chute, A. S., Jacobson, L. D., and Chen, Y. 2008. The Northwest Atlantic deep-sea red crab (Chaceon quinquedens) population before and after the onset of harvesting. – ICES Journal of Marine Science, 65: 862–872.The population structure of deep-sea red crab (Chaceon quinquedens) in a nearly unexploited state is compared with its condition three decades later after more than a decade of sustained harvesting. Our study is based on a camera and net trawl survey conducted in 1974, which we repeated between 2003 and 2005 on the southern New England shelf break. Although the overall biomass of red crabs was estimated to be higher than in 1974, the abundance of large males, which are targeted by the fishery, was considerably lower. In particular, the biomass of large males (≥114 mm carapace width), considered in 1974 to be marketable, declined by 42%. Declines were most evident at depths and regions most accessible to the fishing fleet based in southern New England. With the change in fishery selectivity towards smaller male crabs, the abundance of currently harvestable crabs is about equal to 1974 levels. No declines were observed in the biomass of female and smaller male crabs not targeted by the fishery. Indeed, the abundance of juveniles appears considerably higher than in 1974. Perhaps, adverse effects on reproduction attributable to a reduction in the numbers of large males may be a consequence of fishing, but fishery impacts and productivity are difficult to assess because key biological information is lacking. [ABSTRACT FROM PUBLISHER]

Abstract: This study tests the hypothesis that the scaly projections (scutes) on the shells of juvenile giant fluted clams, Tridacna squamosa, are an adaptation against crushing predators such as crabs. The forces required to crush scutes and clams were measured with a universal testing machine whereas crab chela strength was measured with a digital force gauge connected to a set of lever arms. Results for shell properties and chela strength are used to create two, non-mutually exclusive, predator–defense models. In Model 1, scutes increase the overall shell size, consequently reducing the number of crab predators with chelae that are large enough to seize and crush the prey. In Model 2, the chela has to open more to grasp a prey with these projecting structures which leads to a loss of claw-closing force such that crabs fail to crush the scutes, and consequently the clam. Clam scutes may also deter crab predators by increasing the risk of claw damage and/or handling time. [Copyright &y& Elsevier]

Declining populations of the blue crab, Callinectes sapidus, may be suitable for enhancement with hatchery-reared juveniles. For three years, field experiments were conducted to determine if shallow, unvegetated, marsh-fringed nursery habitats in lower Chesapeake Bay are below carrying capacity and thus capable of supporting additional juvenile crabs. The field experiments included sampling of wild and hatchery-reared juvenile blue crabs and their major benthic prey, and manipulative experiments to assess the survival of juvenile crabs and the abundance of benthic prey in enhanced and control coves. Densities of the clam Macoma balthica, a major prey of the blue crab, were initially high in enhanced coves and decreased to a level equivalent to that in control coves by the end of the experiment, but always remained well above a low-density threshold. Survival of juvenile crabs was lowest where clam densities were highest, suggesting that alternative prey did not deter predation on juvenile crabs, but instead led to higher densities of cannibalistic crabs through bottom-up control. Crab densities correlated with densities of major benthic prey and prey density never dropped below a low-density threshold. Marsh-fringed nurseries are apparently below carrying capacity for the blue crab and could be enhanced through the release of hatchery-reared juveniles. [ABSTRACT FROM AUTHOR]

Aquaculture of the Native Chinese mitten crab (Eriocheir japonica sinensis) has developed quickly in China to reach 570,000 mt in 2005, which exceeds all other worldwide production of crab from aquaculture and capture fisheries combined. We review the development of aquaculture techniques and stock enhancement that account for this successful production of Chinese mitten crabs. There are two models for mitten crab larviculture. In the first model, intensive larviculture occurs in indoor concrete ponds, with conditions of temperature control, aeration, and a plentiful supply of food (algae, egg yolk, rotifers, Artemia nauplii). In the second model, outdoor extensive larviculture occurs in earth ponds with no temperature control. Grow-out of the mitten crab focuses on release of cultured seed crabs into net enclosures in lakes. As a rule, the production of adult crabs is l50-450 kg/ha and as high as 975 kg/ha. Recently, Chinese researchers noticed deterioration of water quality and the exhaustion of natural food resources in many lakes due to over-stocking crabs, and many studies are now beginning to investigate a model for the sustainable aquaculture of Chinese mitten crab in these systems. [ABSTRACT FROM AUTHOR]

Over the last decade, hatchery production of mud crabs has become technically and economically more feasible, enabling evaluation of the potential effectiveness of hatchery release in fisheries enhancement. The high growth rates and limited movement of released crabs mean that fisheries' yields in isolated mangrove systems with restricted recruitment can be enhanced within a few months. Thus, a release program may be an effective strategy for short-term enhancement in carefully selected specific areas. To date, results are very promising, with recovery rates up to 50% and increases in fisheries' yield up to 46% over baseline catches. In contrast, mark-recapture studies in more open mangrove system populations show that recruitment success and subsequent stock abundance may be largely determined by habitat availability. For these populations, restoration of lost or degraded mangrove areas has been shown to be effective in promoting stock recovery through natural recruitment, with replanted mangroves supporting fisheries of equivalent economic value to that of natural mangroves, though it may take some years to reach these levels. Thus, a balanced approach to stock management could integrate both hatchery-release and habitat restoration programs, depending on local conditions and over different time scales, with parallel co-management to support effectiveness. [ABSTRACT FROM AUTHOR]

We compared the capture efficiency and catch dynamics of collapsible square and conical pots used in resource assessment and harvesting of red king crabs (Paralithodes camtschaticus [Tilesius, 1815]) in the Barents Sea. After two days of soaking, square pots caught three times as many crabs as conical pots, and their catches consisted of a higher proportion of male crabs and male crabs larger than 160 mm carapace length compared to the catches in the conical pots. Catches in the square pots did not increase as soak times were increased beyond two days, which indicates equilibrium between the rate of entries into and the rate of exits from the pots. Catches in conical pots, however, increased with increasing soak times up to eight days, the longest soak time examined in this study. These findings demonstrate the higher efficiency of square pots and the importance of understanding catch dynamics when making population assessments based on catchper-unit-of-effort data. The favorable catch characteristics and handling properties of the collapsible square pot may make this pot design suitable for other crab fisheries, as well. [ABSTRACT FROM AUTHOR]