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The marine diatom Haslea ostrearia is known for its ability to produce marennine, a blue-green water-soluble pigment, which is responsible for the oyster greening phenomenon in the French Atlantic Coast. Marennine can be considered a bioactive extracellular compound (BEC) as it exhibits activities against detrimental pathogens in bivalve aquaculture. However, marennine could also be toxic to animals. The aim of this experimental study was to assess the effect of marennine produced by H. ostrearia upon three commercially important bivalve species, the American oyster Crassostrea virginica, the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus. Effect of this BEC was also assessed on different ontogenic stages of scallops. The animals were exposed to 3 mg L−1 of marennine and physiological response associated with clearance rates (CR), oxygen consumption and condition index (CI) were measured after 16 h of exposure (day 0), and after one subsequent week of recovery (day 7). In the short term, CR and oxygen consumption on mussels and oysters were significantly altered by marennine but not for scallops. CR recovery was observed in oysters after seven days, but no depuration was observed in mussels. Nevertheless, oxygen consumption in both mussels and oysters recovered on day 7. CI in the marennine-exposed group for both adult oysters and scallops was not significantly different, yet CI of mussels was lowered by 18.2 % compared to control. Scallop adults seemed largely resistant to marennine, but juveniles were more susceptible with a reduced CR and oxygen consumption by 71.9 % and 24.5 %, respectively, and no depuration activity observed until day 7. Additionally, CI in marennine-exposed juvenile scallops was 27 % lower than that of control. This study demonstrates species- and age-specific effect of marennine on bivalves, thus highlighting the importance of further assessment on the utilization of this pigment as a natural product decreasing pathogenicity of bacteria in shellfish aquaculture systems.

State‐space models (SSMs) are now popular tools in fisheries science for providing management advice when faced with noisy survey and commercial fishery data. Such models are often fitted within a Bayesian framework requiring both the specification of prior distributions for model parameters and simulation‐based approaches for inference. Here we present a frequentist framework as a viable alternative and recommend using the Laplace approximation with automatic differentiation, as implemented in the R package Template Model Builder, for fast fitting and reliable inference. Additionally we highlight some identifiability issues associated with SSMs that fisheries scientists should be aware of and demonstrate how our modelling strategy surmounts these problems. Using the Bay of Fundy sea scallop fishery we show that our implementation yields more conservative advice than that of the reference model. The Canadian Journal of Statistics 47: 27–45; 2019 © 2018 Statistical Society of Canada [ABSTRACT FROM AUTHOR]

We developed a climate-niche species distribution model to evaluate spatiotemporal trends in Atlantic sea scallop (Placopecten magellanicus) along the coastal waters of the Gulf of Maine. We used a Tweedie-generalized additive model (GAM) to quantify the relationships between scallop abundance and key environmental variables. A boosted regression tree was used to identify significant interactions among environmental variables to integrate within the Tweedie GAM and a regional circulation model was incorporated with the Tweedie GAM to hindcast projections of scallop distribution and assess the impacts of environmental change on this species. Additionally, we evaluate two common model fitting and variable selection methods for GAMs to ensure high model performance. A classic backward variable selection procedure was compared to penalized thin plate regression splines. Projections from the climate-niche species distribution model show higher scallop density along inshore areas relative to those farther offshore. An increasing temporal trend in scallop density was observed along inshore areas and a decreasing temporal trend was observed in areas farther offshore. Additionally, we found that the GAM incorporating thin plate regression splines outperformed the widely used backwards stepwise procedure. This modeling framework will help to inform adaptive management strategies for the scallop fishery within the context of a changing Gulf of Maine ecosystem. [ABSTRACT FROM AUTHOR]

Placopecten magellanicus (Gmelin, 1791), a deep-sea Atlantic scallop, holds significant commercial value as a benthic marine bivalve along the northwest Atlantic coast. Recognizing its economic importance, the need to reconstruct its genome assembly becomes apparent, fostering insights into natural resources and generic breeding potential. This study reports a high-quality chromosome-level genome of P. magellanicus , achieved through the integration of Illumina short read sequencing, PacBio HiFi sequencing, and Hi-C sequencing techniques. The resulting assembly spans 1778 Mb with a scaffold N50 of 86.71 Mb. An intriguing observation arises – the genome size of P. magellanicus surpasses that of its Pectinidae family peers by 1.80 to 2.46 times. Within this genome, 28,111 protein-coding genes were identified. Comparative genomic analysis involving five scallop species unveils the critical determinant of this expanded genome: the proliferation of repetitive sequences recently inserted, contributing to its enlarged size. The landscape of whole genome collinearity sheds light on the relationships among scallop species, enhancing our broader understanding of their genomic framework. This genome provides genomic resources for future molecular biology research on scallops and serves as a guide for the exploration of longevity-related genes in scallops. • The high-quality chromosome-level genome of Placopecten magellanicus was firstly reported. • The genome size of P. magellanicus was the largest in the family Fanbeidae. • This scallop had more repetitive sequences and longer intergenic regions. • The highly completed genome assembly potentially benefits biological studies on this species. [ABSTRACT FROM AUTHOR]

Abstract Larval Atlantic sea scallops (Placopecten magellanicus) simulations in the Middle Atlantic Bight (MAB) from 2006 to 2012 were performed to investigate annual and inter-annual dispersal and connectivity patterns among stock regions. These simulations used a circulation model based on the Regional Ocean Modeling System (ROMS) and an individual-based larval model (IBM) that included larval behavior. The circulation model used realistic dynamical forcing (e.g. , winds, tides, and open ocean boundary conditions), thermo-dynamical fluxes (e.g., solar radiations, sensible and latent heating), and hydrological forcing; the larval IBM included vertical swimming and sinking behaviour, temperature-dependent growth, and settlement. Simulated larvae that reach settlement size and suitable habitat in 45 days are considered 'successful', and two regions are considered 'connected' by larval dispersal when larvae successfully disperse from one region to the other. In general, simulated larval dispersal patterns varied seasonally (28% higher in September and October compared to May and June), among years (2007 through 2009 had 5% lower larval success during August and September compared to other years), and spatially, with larvae released from the northern regions like Long Island acting as a substantive larval source with 14% greater dispersal success and 15% greater connectivity with other regions than those released elsewhere. Over the seven years simulated, the MAB scallop stocks showed high rates of connectivity to regions to the south and more limited and variable connectivity to regions to the north. In species like sea scallops with limited adult mobility, larval dispersal supplies recruits, enables range expansion, and connects populations. Thus, appreciation of dispersal patterns are essential for fishery management of this economically valuable stock. [ABSTRACT FROM AUTHOR]

Management of the “General Category” component of the US Atlantic sea scallop (Placopecten magellanicus) fishery changed from open access with a soft, or target, catch limit, to limited access with a hard catch limit, to individual fishing quotas (IFQs) in just three years. Two differences-in-differences (DiD) models are used to examine the causal effects of management on price and revenue. A hedonic price model finds that the IFQ program had minimal direct effects on prices. A landings composition model finds that the IFQ program increased landings of the largest scallops. The Limited Access fleet, which lands most of the scallops in the region and is managed primarily with input controls, serves as a control for both models. Our policy simulation finds that IFQs increased revenues by 2.6% compared to hard catch limits. However, the IFQ program did not increase revenues relative to the regulated open-access system. [ABSTRACT FROM AUTHOR]

Abstract: Environmental factors can influence diversity and population structure in marine species and accurate understanding of this influence can both improve fisheries management and help predict responses to environmental change. We used 7163 SNPs derived from restriction site‐associated DNA sequencing genotyped in 245 individuals of the economically important sea scallop, Placopecten magellanicus, to evaluate the correlations between oceanographic variation and a previously identified latitudinal genomic cline. Sea scallops span a broad latitudinal area (>10 degrees), and we hypothesized that climatic variation significantly drives clinal trends in allele frequency. Using a large environmental dataset, including temperature, salinity, chlorophyll a, and nutrient concentrations, we identified a suite of SNPs (285–621, depending on analysis and environmental dataset) potentially under selection through correlations with environmental variation. Principal components analysis of different outlier SNPs and environmental datasets revealed similar northern and southern clusters, with significant associations between the first axes of each (R2adj = .66–.79). Multivariate redundancy analysis of outlier SNPs and the environmental principal components indicated that environmental factors explained more than 32% of the variance. Similarly, multiple linear regressions and random‐forest analysis identified winter average and minimum ocean temperatures as significant parameters in the link between genetic and environmental variation. This work indicates that oceanographic variation is associated with the observed genomic cline in this species and that seasonal periods of extreme cold may restrict gene flow along a latitudinal gradient in this marine benthic bivalve. Incorporating this finding into management may improve accuracy of management strategies and future predictions. [ABSTRACT FROM AUTHOR]

Sea scallops (Placopecten magellanicus) live along the Northwest Atlantic continental shelf and are aggregated over a broad range of spatial scales (m²-105 km²). However, little is known about the spatial distribution of local scallop neighborhoods, the scale at which spawning, intra-specific competition, and predator-prey interactions occur. We surveyed 30,995 km² of Georges Bank and the Great South Channel annually from 2003 to 2010 counting the number of scallops in 54,016 locally replicated 3.24-m² quadrats with underwater video. There were about 4 billion scallops occupying 11,200 km² of the study area in concentrations from 1 to 41 scallops per scallop. Scallop spatial distribution switched from dispersed to aggregated at a concentration of 3-4 scallops in every year. High concentrations (>3) occurred in 11% but were only persistent in 4% (449 km²) of scallop habitat. There were 13 persistent high-concentration aggregations (7-217 km²), and all but two occurred on gravel-dominated sediments left by prehistoric glacial retreat. Model-derived benthic boundary shear stresses in the persistent aggregations averaged two times higher than in scallop habitat, but the seabed was about two times more stable because it had significantly less sand and more granule-pebble and cobble sediment. The area occupied by scallops each year varied little (9%) despite a 49% increase in total scallop abundance between 2005 and 2007, suggesting Georges Bank scallops have a proportional density population structure. Most scallops occurred alone or at low concentrations (=2) where fertilization success is probably poor. The persistent high-concentration aggregations we identified may be critical for successful reproduction and sustainable harvest. Observing organisms at scales corresponding to their individual interactions reveals important processes shaping their landscape-scale spatiotemporal distributions. These processes are obscured by the methods typically employed to estimate abundances of commercial fishery species. The spatiotemporal structure of sea scallop distribution has important implications for the design of abundance surveys and the assumptions underlying stock assessment methods. These should be investigated. Finally, this work suggests that natural disturbance (sediment stability) may play a substantial role in shaping spatiotemporal distributions and dynamics of benthic marine populations. [ABSTRACT FROM AUTHOR]

An invasive colonial tunicate (Didemnum vexillum) was initially observed on Georges Bank in 1998, and it has since spread in benthic environments on fishing grounds and areas closed to bottom-fishing. It can form dense mats on gravel substrates that are also a preferred habitat for the Atlantic sea scallop (Placopecten magellanicus), which supports one of the most valuable commercial fisheries in the United States. We used HabCam, a vessel-towed underwater imaging system, to investigate the spatial distributions of P. magellanicus and D. vexillum in a region that includes fishing grounds and an area protected from bottom-fishing. We found a negative relationship between P. magellanicus and D. vexillum, even after controlling for substrate and management status, suggesting that D. vexillum competes for habitat with P. magellanicus. We also applied the geostatistical method of universal kriging to interpolate the distribution of D. vexllium based on the covariables gravel, depth and area. Our results indicate that D. vexillum is more common in areas open to fishing than in the areas closed to fishing, even taking bottom substrate effects into account. Didemnum vexillum appears to have spread over portions of the northern edge of Georges Bank. This research evaluates potential fish and invertebrate habitat degradation caused by an invasive species. [ABSTRACT FROM AUTHOR]

Most stock assessment models assume that the probability of capture for all individuals of the same size or age in the stock area is equal. However, this assumption is rarely, if ever, satisfied. We used spatially referenced simulations, based on the US Atlantic sea scallop ( Placopecten magellanicus) fishery, to generate catch, survey index, fishing effort, and size structure data that we input into a (nonspatial) catch-at-size stock assessment model to estimate abundance and mortality rates. We show that spatial patterns in fishing mortality degrade model performance for sessile stocks. Fishing mortality tended to be overestimated and abundance underestimated because trends in fishing mortality were exaggerated and the model misestimated the numbers of larger individuals due to spatial fishing patterns. These results are particularly relevant to sedentary species such as scallops, but are applicable wherever strong spatial patterns exist in fishing mortality. [ABSTRACT FROM AUTHOR]

Management for the major sea scallop ( Placopecten magellanicus) fisheries in Canada is based on maximum sustainable yield (MSY) biomass and fishing mortality reference points applied to the whole stock, under the assumption that fishing mortality is uniformly distributed in space. However, scallop fishing vessels concentrate fishing in areas that consistently exhibit high densities resulting in a nonuniform spatial distribution of fishing effort. This study applies a spatial model for fishing effort derived from satellite vessel monitoring system data, scallop habitat suitability maps, and relative scallop density from a spatial stock assessment model to evaluate precautionary approach reference points in support of sustainable management. Target harvest rates were evaluated in terms of MSY for the higher habitat suitability areas. The results indicated that although MSY for the spatial model were similar to those when assuming a uniform distribution of effort, the biomass and catch rates over all areas were higher. The spatial model predicted that the MSY would be taken with less fishing effort, potentially lessening the benthic impacts from the scallop fishery. [ABSTRACT FROM AUTHOR]

Understanding patterns of dispersal and connectivity among marine populations can directly inform fisheries conservation and management. Advances in high-throughput sequencing offer new opportunities for estimating marine connectivity. We used restriction-site-associated DNA sequencing to examine dispersal and realized connectivity in the sea scallop Placopecten magellanicus, an economically important marine bivalve. Based on 245 individuals sampled rangewide at 12 locations from Newfoundland to the Mid-Atlantic Bight, we identified and genotyped 7163 single nucleotide polymorphisms; 112 (1.6%) were identified as outliers potentially under directional selection. Bayesian clustering revealed a discontinuity between northern and southern samples, and latitudinal clines in allele frequencies were observed in 42.9% of the outlier loci and in 24.6% of neutral loci. Dispersal estimates derived using these clines and estimates of linkage disequilibrium imply limited dispersal; 373.1 ± 407.0 km (mean ± SD) for outlier loci and 641.0 ± 544.6 km (mean ± SD) for neutral loci. Our analysis suggests restricted dispersal compared to the species range (>2000 km) and that dispersal and effective connectivity differ. These observations support the hypothesis that limited effective dispersal structures scallop populations along eastern North America. These findings can help refine the appropriate scale of management and conservation in this commercially valuable species. [ABSTRACT FROM AUTHOR]

The concentration patterns in the Northeast U.S. sea scallop industry are examined from 1996-2014 using generalized indices of concentration and exploratory spatial data analysis. Absolute and relative Theil indices of concentration are computed to describe the regional pattern of concentration within ports over time. Moran's I provides a complementary measure of concentration of activity among neighboring ports. The Moran scatterplots and confidence plots provide insight into local patterns of concentration in this industry. The analysis reveals large changes from year to year in the geographic concentration of the scallop industry, which is likely to be related to natural variability of the environment and regulations enacted by fisheries managers in response to the variability of the environment. [ABSTRACT FROM AUTHOR]

The clinically important anticoagulant heparin, a member of the glycosaminoglycan family of carbohydrates that is extracted predominantly from porcine and bovine tissue sources, has previously been shown to inhibit the β-site amyloid precursor protein cleaving enzyme 1 (BACE-1), a key drug target in Alzheimer's Disease. In addition, heparin has been shown to exert favourable bioactivities through a number of pathophysiological pathways involved in the disease processes of Alzheimer's Disease including inflammation, oxidative stress, tau phosphorylation and amyloid peptide generation. Despite the multi-target potential of heparin as a therapeutic option for Alzheimer's disease, the repurposing of this medically important biomolecule has to-date been precluded by its high anticoagulant potential. An alternative source to mammalian-derived glycosaminoglycans are those extracted from marine environments and these have been shown to display an expanded repertoire of sequence-space and heterogeneity compared to their mammalian counterparts. Furthermore, many marine-derived glycosaminoglycans appear to retain favourable bioactivities, whilst lacking the high anticoagulant potential of their mammalian counterparts. Here we describe a sulphated, marine-derived glycosaminoglycan extract from the Atlantic Sea Scallop, Placopecten magellanicus that displays high inhibitory potential against BACE-1 (IC 50 = 4.8 μg.mL−1) combined with low anticoagulant activity; 25-fold less than that of heparin. This extract possesses a more favourable therapeutic profile compared to pharmaceutical heparin of mammalian provenance and is composed of a mixture of heparan sulphate (HS), with a high content of 6-sulphated N-acetyl glucosamine (64%), and chondroitin sulphate. [Display omitted] • A GAG extract from the Atlantic Sea Scallop, P. magellanicus , inhibits BACE-1, a key drug-target in Alzheimer's disease. • The GAG extract is predominantly HS, containing a high content of UA-GlcNAc(6S), uncommon in mammalian-derived HS. • The GAG extract possesses highly attenuated anticoagulant potential compared to mammalian-derived heparin. [ABSTRACT FROM AUTHOR]

Atlantic sea scallop ( Placopecten magellanicus ) meats are normally firm and creamy white. However, scallops with small, darkened and stringy adductor muscle (gray meat) episodically occur along the Eastern Seaboard, most recently in the rotational management areas of Georges Bank after extended fishing closures. These gray meat scallops are associated with reduced harvestable biomass and mass mortality events. We tested age, nutritional stress and disease as causative agents for this condition. Adult scallops of different shell heights (SH) ranging from (90–145 mm) were collected from Georges Bank and analyzed for meat quality and the presence of pathogens using biochemical, histopathological and molecular methods. Gray meat occurrence was weakly correlated with shell height only explaining 8.49% of the variance in a generalized additive model (GAMS). Gray meat weights were lower than white meat (p < 0.001) and there was a dramatic reduction in protein content (p < 0.05) in gray meat scallops associated with extensive myodegeneration. Amino acid profiles confirmed the breakdown of muscle tissue with an increase in free hydroxyproline in gray meat scallops. Infection by an apicomplexan parasite was detected in the muscle tissue of all gray meat scallops tested. An intermediate pathology stage (brown meat) was also identified. As the parasitic infection increased, meat quality decreased. Numerous developmental stages of the parasite were present in various organs of the scallops. This apicomplexan has an identical SSU rDNA sequence to a novel parasite occurring in the Iceland scallop during a recent mass mortality event. The range of this parasite in Atlantic sea scallops and the effect of abiotic/biotic stressors on pathogenicity are currently unknown. Results from this study link an apicomplexan species, known to be highly pathogenic in scallops, to gray meat occurrence with a potentially high impact on the fishery. [ABSTRACT FROM AUTHOR]

This paper explores the possibility of using the supernatant of Haslea ostrearia culture containing marennine, a natural microalgal pigment, as an antimicrobial in bivalve hatcheries. The blue mussel Mytilus edulis and the scallop Placopecten magellanicus were used as model animals, and the pathogenic marine bacteria Vibrio splendidus was used to induce larval mortality. The hypothesis tested was that V. splendidus pathogenicity in larval rearings can be controlled by using marennine-containing culture supernatants. The effect of three marennine concentrations was tested on a larval rearing over 20 days for M. edulis and 9 days for P. magellanicus. At a low dose (0.1 mg L-1), survival and physiological condition were both higher than in the control. In bacterial challenges, larvae were exposed to V. splendidus for 72 h, with or without marennine. The bacterial challenge caused significant mortality when compared to controls, while the marennine-treated larvae showed significantly higher survival. Results show that marennine is an interesting molecule for pathogen control in hatcheries as it is active at low concentrations and significantly enhanced larval survival and physiological condition. [ABSTRACT FROM AUTHOR]

The sea scallop (Placopecten magellanicus) fishery in the Atlantic is assessed during annual surveys by using both dredging and surface-deployed imaging techniques. In this pilot study in the Mid-Atlantic Bight, we used an autonomous underwater vehicle (AUV) to photograph the seafloor and to evaluate its use for determining scallop density and size. During 22 surveys in 2011, 257 km of seafloor were photographed, resulting in over 203,000 color images. Using trained annotators and photogrammetric software, we determined scallop density and shell heights for 15,252 scallops. The inshore scallop grounds near Long Island (at depths <40 m) had a density of 0.077 scallops per m2, whereas the inshore grounds of the New York Bight had a density of 0.012 scallops per m2. Shell heights derived from images were found to agree well with measurements from scallops collected with a commercial dredge. We show that images obtained with an AUV can be used to reliably estimate both density and shell height consistent with direct sampling from the same area. Moreover, side-scan sonar images obtained with an AUV can be used to detect dredge scars and, therefore, can provide a simultaneous, relative estimate of fishing effort in that area. AUVs provide a highly accurate suite of data for each survey site and therefore allow the design of experimental studies of fishing practices. [ABSTRACT FROM AUTHOR]

Conventional yield-per-recruit (Y/R) and spawning-stock biomass-per-recruit (SSB/R) models make no allowance for spatial heterogeneity in fishing mortality, natural mortality, or growth across the stock area, although variability in these processes can affect model results. For example, areas with higher growth and/or lower natural mortality rates should be fished at a lower rate to maximize Y/R; however, these areas may be especially attractive to fishers and are often fished harder. Here, Y/R and SSB/R models are developed that simultaneously account for spatial heterogeneity in growth and fishing effort. These models are applied to the US Atlantic sea scallop (Placopecten magellanicus) fishery. The spatial variability in growth uses depth-integrated models from the literature and variability in effort is based on, alternatively, uniform, observed, and relative-optimal spatial harvesting distributions. The observed effort patterns are derived from vessel monitoring system positions, and illustrate one application for these widely collected but underutilized spatial data. In this example, the distribution of observed fishing effort reduces Y/R compared with the relative-optimal, or the uniform effort distribution implicitly assumed by conventional Y/R analysis. SSB/R was in some cases considerably higher under the relative-optimal distribution of effort than when calculated using observed or uniform effort patterns. Such more realistic spatially integrated Y/R and SSB/R models can help to evaluate the impact of effort patterns on fishery yield and stock egg production. These models demonstrate that the spatial distribution of effort can be as important as the overall average fishing mortality when managing fisheries to optimize Y/R, SSB/R, and yield. [ABSTRACT FROM AUTHOR]

We estimate temporally varying natural mortality within a size-based stock assessment model for U.S. sea scallops in three different regions, and compare the results to corresponding models where natural mortality is not estimated, and (in one case) where only the mean natural mortality is estimated. In one model, for the Georges Bank Closed Areas, natural mortality was estimated by year for all sizes, whereas in the other two models (for the Georges Bank Open Areas and the Mid-Atlantic Bight), annual variation in natural mortality was estimated for juveniles only. Estimating natural mortality by year improved the performance over fixed natural mortality in all three models, as measured by Akaike's information criterion (AIC) and reduced retrospective patterns. There was evidence that natural mortality is density-dependent. Large recruitment events were associated with substantial increases in juvenile natural mortality, and natural mortality in the Georges Bank Closed Areas tended to increase at high biomass. Estimation of natural mortality was facilitated by survey data that gave estimates of absolute abundance together with low fishing mortality that minimized the confounding between natural and fishing mortality. Natural mortality is an important process that should be estimated when there is sufficient information to do so. [ABSTRACT FROM AUTHOR]

Quantifying the distribution and abundance of the Atlantic sea scallop (Placopecten magellanicus) is a fishery management priority, and stock assessments increasingly rely on video surveys. Interpreting the results of these surveys requires understanding the inherent biases introduced as a result of target animal behaviour. Our study investigated the effect of artificial lights on the behaviour of Atlantic sea scallops during a video survey using a towed benthic sled. Swimming and stationary scallops were counted in survey videos using event logging software. In addition, the locations, orientations, and swimming directions of the scallops were noted in a subset of the videos. The proportion of scallops that swam when an artificial light was turned on was significantly smaller than the proportion that swam when the light was off. Further analysis using a logistic model showed that only light state (off or on) predicted the likelihood of scallop swimming responses. Possible reasons for this unexpected behaviour are discussed, with a focus on the scallop visual system. [ABSTRACT FROM AUTHOR]

This study examined whether a measured increase in average body size of adult sea scallops inside three fishery closed areas on Georges Bank (GB), United States (US), was sufficient to increase larval supply to closed areas and open fishing areas in both US and Canadian areas of the Bank. The effects of adult scallop density-at-size and fecundity-at-size on egg production were compared among open and closed fishery areas, countries, and time periods before and after the closed areas were established. Estimated egg production was then used to define spawning conditions in a coupled biological-physical larval tracking model that simulated larval development, mortality, and dispersal. Results showed that order of magnitude increases in larval settlement after closure were facilitated by increases in size-dependant egg production inside and dispersal from Closed Areas I and II, but not Nantucket Lightship Closed Area. The distributions of both egg production and larval settlement became more uniform across the Bank, causing the relative contribution of Canadian larvae to US scallop aggregations to decrease after establishment of Closed Areas I and II. Decreases in small and medium-sized scallop density in Canada and decreases in large scallops over the US-Southern Flank after closure caused local declines in egg production but were not sufficient to negatively affect larval settlement at the regional scale. Our model suggests that the establishment of fishery closed areas on GB considerably strengthened larval supply and settlement within and among several adult scallop aggregations. [ABSTRACT FROM AUTHOR]

To assess whether giant scallops, Placopecten magellanicus use distinct escape strategies to respond to their seastar and crustacean predators, escape responses to two major seastar predators, Asterias vulgaris and Leptasterias polaris, two seastars with little predatory impact, Crossaster papposus and Solaster endeca, and two crustacean predators, Cancer irroratus and Hyas araneus were compared. A glass rod served as a mechanical control. The responses of juvenile [2+ year (y), ~36-mm shell height (SH)] and adult (6+ y, ~100-mm SH) scallops from the Magdalen Islands, Québec, Canada, were assessed in early summer 2005. The predatory seastars evoked the strongest response, in terms of both response latency and minimum interval between phasic contractions and numbers of phasic contractions, particularly early in the escape response. Both the minor seastar predators and crabs stimulated stronger responses than the mechanical control. Juvenile scallops were livelier than adult scallops. As P. magellanicus consistently responded to predators with an initial flurry of phasic contractions that tapered off to spaced phasic contractions separated by increasingly long tonic contractions, only the intensity of the escape response seems to have been modified by selection. [ABSTRACT FROM AUTHOR]

Ocean acidification, the progressive change in ocean chemistry caused by uptake of atmospheric CO2, is likely to affect some marine resources negatively, including shellfish. The Atlantic sea scallop (Placopecten magellanicus) supports one of the most economically important single-species commercial fisheries in the United States. Careful management appears to be the most powerful short-term factor affecting scallop populations, but in the coming decades scallops will be increasingly influenced by global environmental changes such as ocean warming and ocean acidification. In this paper, we describe an integrated assessment model (IAM) that numerically simulates oceanographic, population dynamic, and socioeconomic relationships for the U.S. commercial sea scallop fishery. Our primary goal is to enrich resource management deliberations by offering both short- and long-term insight into the system and generating detailed policy-relevant information about the relative effects of ocean acidification, temperature rise, fishing pressure, and socioeconomic factors on the fishery using a simplified model system. Starting with relationships and data used now for sea scallop fishery management, the model adds socioeconomic decision making based on static economic theory and includes ocean biogeochemical change resulting from CO2 emissions. The model skillfully reproduces scallop population dynamics, market dynamics, and seawater carbonate chemistry since 2000. It indicates sea scallop harvests could decline substantially by 2050 under RCP 8.5 CO2 emissions and current harvest rules, assuming that ocean acidification affects P. magellanicus by decreasing recruitment and slowing growth, and that ocean warming increases growth. Future work will explore different economic and management scenarios and test how potential impacts of ocean acidification on other scallop biological parameters may influence the social-ecological system. Future empirical work on the effect of ocean acidification on sea scallops is also needed. [ABSTRACT FROM AUTHOR]

Fishery-dependent catch per unit effort (CPUE) comprises critical input for many stock assessments. Construction of CPUE indices usually employs some method of data standardization. However, conventional methods based on linear models do not effectively deal with the fact that samples are collected with a selection bias or with the problem of filling spatial gaps. Geostatistical interpolation methods can ameliorate some of the biases caused by both of these problems while remaining complementary to traditional linear model-based CPUE standardization. In this paper we present geostatistical estimates of sea scallopPlacopecten magellanicusCPUE from tows recorded by onboard observers during an opening of Georges Bank Closed Area II in 1999. By selecting tows for which there was little prior effort (on the basis of accumulated effort measured by vessel monitoring systems), we obtained tows that reflected initial abundance as closely as possible. These tows were used to obtain a variogram which was used in geostatistical prediction of sea scallop CPUE. The kriged mean was substantially lower than the arithmetic sample mean, indicating that a geostatistical approach reduced the influence of repeated sampling in locations of extremely high CPUE and increased the weight of isolated observations in areas of low CPUE. The results produced a map that was qualitatively similar to that obtained from a preseason fishery-independent survey. Overall differences between the two approaches were driven by the extension of predictions into areas at the edges of spatial autocorrelation where kriging predictions approached the grand mean of the data set. Received July 26, 2013; accepted June 2, 2014 [ABSTRACT FROM AUTHOR]

Size distribution and swimming activity of the sea scallop, Placopecten magellanicus, were measured in situ from high-definition video recordings collected by a remotely operated vehicle on a fished scallop bed on German Bank, Gulf of Maine in August 2010. Scallop densities ranged from 0.004 to 3.89 m−2 and shell height (SH) ranged from 16.3 to 193.8 mm. The size distribution was bimodal, with high abundance from 20 to 40 mm SH indicating a recent recruitment event in the area. The low abundance of scallops >100 mm SH was likely due to the active fishery in this area. Of 535 observed swims, 200 were characterized for swim distance, time, velocity and distance travelled per adduction. The size of scallops observed to swim ranged from 18.9 to 99.9 mm SH. Both swim time and swim distance increased linearly with SH, and quadratic relationships were observed between velocity and SH, and between distance travelled per adduction and SH. Swimming velocities peaked at ~ 50 cm s−1 for scallops between 60 and 80 mm, and maximum velocity was 103.2 cm s−1observed for an individual of 64.0 mm SH. Our study provided a unique opportunity to investigate size distribution and associated swimming activity of scallops in their natural habitat, rather than in a simulated study in the laboratory, and at depths not reachable by SCUBA diving. [ABSTRACT FROM PUBLISHER]

Abstract: To protect public health from the potential risk of paralytic shellfish poisoning (PSP) in sea scallops, Placopecten magellanicus, from the Atlantic offshore U.S. waters of Georges Bank, harvesting of roe-on or whole scallops is banned. Only adductor muscles may be sold if harvested from Georges Bank, Gulf of Maine, or the PSP closure areas as far west as 71° West Longitude. Given the limited toxicity data available for sea scallops from this region both prior to and subsequent to implementation of this management strategy, this study sought a more extensive spatial and temporal evaluation of sea scallop gonad and viscera toxicities that would inform management decisions related to the roe-on and whole scallop fishery. Both overall toxicity and toxin composition were measured for sea scallop gonads and viscera collected from 232 stations in 2007 and 23 in 2010. Overall toxicity was assessed using two screening methods: field-deployable Jellett Rapid Tests (JRT) and quantitative, laboratory-based receptor binding assays (in 2007). Additionally, a quantitative liquid chromatography with fluorescence detection (LC-FD) method was used to determine toxin composition and overall toxicity (in 2010). The at-sea qualitative JRT screening tool results, whereby a positive indicated the sample contained at least 40μg saxitoxin (STX) equivalents 100g−1, were often inconsistent with results obtained using the quantitative methods. Sea scallop viscera toxicity represented the majority of toxin load in the organism and was often in excess of the regulatory guidance level. Sea scallop gonads accounted for a small percentage of total toxicity, but at times reached unsafe levels. Toxin composition in both the gonads and viscera was dominated by STX and gonyautoxin 2/3, as has been reported in previous studies. No predictive indices of gonad toxicity were found. Results at this time do not support a roe-on or whole scallop fishery on Georges Bank. While access restrictions to whole scallops on Georges Bank are unlikely to change based on these results, it seems plausible that a management strategy requiring at-sea testing of scallop gonads for PSP may be necessary in order for a safe roe-on scallop fishery from this region to be feasible. [Copyright &y& Elsevier]