Placopecten Magellanicus Research Articles

Spillover of sea scallops from rotational closures in the Mid-Atlantic Bight (United States)

AbstractWe examined evidence for larval spillover (increased recruitment outside the closures) of Atlantic sea scallops (Placopecten magellanicus) due to rotational closures in the Mid-Atlantic Bight using a 40-year fisheries survey time series and a larval transport model. Since the first closure of the Hudson Canyon South (HCS) area in 1998, mean recruitment in the two areas directly down-current from this closure, Elephant Trunk (ET) and Delmarva (DMV), increased significantly by factors of about 7 and 2, respectively. Stock–recruit plots indicate that low biomasses in HCS were associated with reduced mean recruitment in ET and DMV. Simulations indicate that larvae spawned in HCS often settle in the two downstream areas and that model-estimated settlement (based on gonad biomass in HCS and year-specific larval transport between the areas) is correlated with observed recruitment. This study gives strong evidence that the rotational closure of HCS has induced increased recruitment in down-current areas.

The Black Sea Flexopecten species-complex (Mollusca: Bivalvia: Pectinidae): Shell morphology and 16S rDNA variation

The taxonomic status and population variability of a Black Sea scallop (Flexopecten: Mollusca, Pectinidae) was evaluated in a DNA barcoding study using the 16S ribosomal DNA gene (=16S rDNA), in conjunction with seven morphological features of the shell. We conclude that the Black Sea form represents an eastern extension of the Mediterranean scallop F. glaber (Linnaeus, 1758). It is characterized by a significant lack of genetic variability when compared to the Mediterranean form, although it does contain new haplotypes not found in that species. There is also an increase in the mismatch in the distribution of nucleotides for the Black Sea form when compared with pooled samples of Mediterranean scallop. Plausible reasons for the observed phenomena are hypothesized from the standpoint of the epigenetic theory of evolution and the time since the scallop penetrated into the Black Sea. The lack of genetic variability is potentially due to founder effect and genetic drift.

Investigating uncertainties created by camera improvement in an optical survey

AbstractFish are an essential source of global food. Fishery‐independent data is critical to fisheries assessment and management. The uncertainties created by changing methods to collect this data must be understood. In the U.S. Northeast Atlantic, a drop camera survey of Atlantic sea scallops is a critical source of fishery‐independent data. From 1999 to 2016 the primary sampling unit of the survey was an analog 2.8 m2 image. In 2017 this image was replaced with a digital 2.3 m2 image. Here the key uncertainties associated with this change, an increased ability to detect small scallops and altered estimates of size frequencies and densities due to the survey's methods in the context of the smaller image size, are explored. Scallop detection differences were quantified using a maximum likelihood model and paired analog and digital images. The proportion of scallops measured by size in actual and simulated data and different methods of counting scallops along the edges of images were compared to explore these uncertainties. More scallops were detected in the digital images until scallops were greater than 75 mm in shell height, indicating the models developed here are needed to adjust scallop counts for analysis incorporating juveniles and data from the two cameras. The proportion of scallops measured did not match the simulation and was not linked to quadrat size. There was no significant difference in scallop density with different counting methods. This investigation spurred by altering the methods of a well‐established survey provided confidence in results with potential avenues for fine‐tuning.

Single and Repeated Dose 28-Day and 13-Week Toxicity Studies of Oil Prepared from the Internal Organs of the Japanese Giant Scallop (Patinopecten yessoensis) in Mice.

Internal organs of discarded scallops are rich in omega-3 polyunsaturated fatty acids, but it is not used as a food ingredient due to the presence of toxic substances. Recently, our research team prepared high-quality scallop oil (SCO) from the internal organs of the Japanese giant scallop (Patinopecten yessoensis), in which cadmium and diarrhetic shellfish toxin are below regulated levels. In this study, SCO was prepared from the internal organs of scallops obtained from Mutsu and Uchiura bays in Japan, and was referred to as SCO-M (scallop oil from Mutsu bay) and SCO-U (scallop oil from Uchiura bay), respectively. Acute and subacute toxicity studies were performed to assess the safety of the prepared SCO. In acute toxicity study, mice were orally administered SCO-M and SCO-U at a single dose of 5,000 mg/kg body weight. In a 28-day repeated oral dose toxicity study, the mice were fed diets containing 1% and 5% SCO-M and SCO-U; and in a 13-week repeated oral dose toxicity study, the mice were fed 5% SCO-M and SCO-U. There were no toxicologically significant changes in clinical signs, hematology, blood chemistry, and organ weights at any dose during the experiment. Therefore, it was concluded that SCO-M and SCO-U are safe for use as food ingredients under the experimental conditions of this study.

An ensemble high‐resolution projection of changes in the future habitat of American lobster and sea scallop in the Northeast US continental shelf

AbstractAimTo address the uncertainty associated with climate‐driven biogeographical changes in commercial fisheries species through an ensemble species distribution modelling (SDM) approach.LocationNortheast US Continental Shelf Large Marine Ecosystem (NEUS‐LME).MethodsWe combined an ensemble SDM platform (BIOMOD 2) and a high‐resolution global climate model (NOAA GFDL CM2.6) to quantify spatiotemporal changes in habitat of two commercially important species in the Northeast US Continental Shelf Large Marine Ecosystem (NEUS‐LME); American lobster (Homarus americanus); and sea scallop (Placopecten magellanicus). An ensemble SDM was calibrated using multi‐decadal fisheries‐independent surveys (1984–2016). Statistically weighted species‐specific ensemble SDM outputs were combined with 80 years of projected bottom temperature and salinity changes in response to a high greenhouse gas emissions scenario (an annual 1% increase in atmospheric CO2).ResultsStatistically significant changes (p < .05) in habitat suitability for both species were found over a large portion of the study area. Sea scallop undergoes a northward shift over the study period, while American lobster moves further offshore. The ensemble projections showed that several management zones were identified with increases and decreases in species‐specific habitat. Uncertainty due to variations in ensemble member models was also found in the direction of change within each management zone.Main conclusionsThis study provides ensemble estimates of climate‐driven changes and associated uncertainties in the biogeography of two economically important species in the United States. Projected climate change in the NEUS‐LME will pose management challenges, and our ensemble projections provide useful information for climate‐ready management of commercial fisheries.

Does trace element composition of bivalve shells record utra-high frequency environmental variations?

Saint-Pierre and Miquelon (SPM) is a small archipelago where instrumental measures based on water column velocity and temperature profiles compiled comprehensive evidence for strong near-diurnal (25.8h) current and bottom temperature oscillations (up to 11.5 °C) which is possibly the largest ever observed — at any frequency — on a stratified mid-latitude continental shelf. The main objective of our study was to identify if Placopecten magellanicus can record on its shell these high frequency environmental variations. To this end, we have tried to identify proxies for water temperature and food availability through development of a new ultra-high resolution LA-ICPMS analyses method capable of resolving shell surface elemental composition with a 10 μm resolution. This method was applied on two shell fragments, both representing the third year of growth and 2015 annual growth period, respectively coming from two environmentally contrasted sites, more (30 m depth) or less (10 m depth) affected by high frequency thermal oscillations. Our results strongly suggest a relationship between phytoplankton biomass and barium incorporation into P. magellanicus shells at both sites. Even if P. magellanicus might present a physiological control of magnesium incorporation, the shape of the two Mg/Ca profiles seems to illustrate that temperature also exerts a control on magnesium incorporation in P. magellanicus shells from SPM. While U/Ca and Mg/Ca profiles show a strong positive correlation for 30 m site shell, suggesting that uranium incorporation in P. magellanicus shell is at least partially temperature dependent. The absence of such correlation for 10 m site shell suggests differences in uranium environmental availability or in P. magellanicus biomineralization between these two sites. The resolution of this new analytical method raises questions about such data interpretation related to P. magellanicus growth dynamics and physiology or individual scale based environmental measurements.

Repeated 28-day and 13-week dose toxicity studies of oils prepared from the internal organs of the Japanese giant scallop (<i>Patinopecten yessoensis</i>) in rats

Repeated 28-day and 13-week dose toxicity studies of oils prepared from the internal organs of the Japanese giant scallop (<i>Patinopecten yessoensis</i>) in rats

Selectivity of Two Commercial Dredges Fished in the Northwest Atlantic Sea Scallop Fishery

Size selectivity curves were estimated for two commercial dredge configurations used in the United States Atlantic sea scallop (Placopecten magellanicus) fishery. Traditionally, the New Bedford Style dredge (New Bedford dredge) has been used by the commercial fleet; however, since 2013, the Coonamessett Farm Turtle Deflector Dredge (turtle dredge) has been required seasonally in the Mid-Atlantic region to minimize the capture of sea turtles. This analysis provides estimates of selectivity and relative efficiency for the turtle dredge and the New Bedford dredge. Selectivity information for the turtle dredge is currently unknown, and selectivity for the New Bedford dredge was originally assessed in 2008. The Share Each Lengths Catch Total method was used to model scallop catch-at-length data for each commercial dredge with data collected during the Virginia Institute of Marine Science fishery-independent surveys in 2015 to 2017, conducted onboard commercial fishing vessels. The surveys were conducted in the Mid-Atlantic and Georges Bank regions of the resource in three distinct areas. A paired study design was used, where a nonselective National Marine Fisheries Service sea scallop survey dredge and either the turtle dredge or New Bedford dredge were towed simultaneously at each survey station. To assess for time-varying changes in selectivity, results were compared with the 2008 New Bedford dredge analysis. Results indicated the 50% retention length was 98.2 mm, with a selection range of 28.2 mm and a relative efficiency of 0.83 for the turtle dredge. New Bedford dredge results estimated a 50% retention length of 107.4 mm, selection range of 50.5 mm and relative efficiency of 0.81. Comparing selectivity profiles for the turtle dredge and New Bedford dredge with the 2008 results indicated a shift toward increased retention probability for smaller size classes of scallops.

Improving scallop (Pecten maximus and Placopecten magellanicus) spat production by initial larvae size and hydrodynamic cues used in nursery system

There are several factors affecting scallops during the metamorphosis process that could explain the relatively low post-larvae yield observed in hatcheries. Competent bivalve larvae respond to different settlement cues to undergo metamorphosis and without adequate cues, larvae delay their metamorphosis. The objective of this study is to improve the settlement ratio of the two scallop species, Placopecten magellanicus and Pecten maximus by physical cues associated with hydrodynamic conditions, stocking density in settlement units and larval size at time of transfer to settling units. For each treatment, physiological condition was determined by fatty acid analysis to determine the energetic reserves and structural lipids. We observed similar results for the two important commercial pectinid species and validate the hypothesis on the positive effect of increased flow rate and larval size after transfer to settlement systems on settlement success. Increasing flow rate also affects positively the physiological condition of settled post-larvae by a higher accumulation of total fatty acids in neutral lipid fractions. Furthermore, no effect of larval stocking density until 90 larvae cm−2 in the downwelling sieves was observed. To our knowledge this study is the first to characterize the effect of seawater flow rate on settlement success of different pectinid species cultured under similar conditions. The experiments were performed in a close to commercial scale and thus are relevant to industry situations.

Investigating the Impact of Multiple Factors on Gray Meats in Atlantic Sea Scallops (Placopecten magellanicus)

The Atlantic sea scallop fishery is the one of the most valuable fisheries in North America. There is concern about scallops with low-quality adductor muscles, referred to as gray meats, impacting the fishery and the overall health of the stock because an apicomplexan parasite has been linked to gray meats and a mass mortality event that led to the collapse of the Icelandic scallop fishery. Yet, changes in scallop meat color have also been linked to the depletion of energy reserves in the adductor muscle following spawning. Seasonal scallop dredge surveys were conducted across Georges Bank, collecting data on scallop meat quality, scallop abundance, mortality, and reproductive cycles, as well as environmental parameters, including bottom depth and temperature. To investigate multiple causes for gray meats, a set of models were developed to examine the impact of biotic and abiotic factors on gray meat prevalence and meat quality of individual scallops. Model results indicate that different factors influence gray meat prevalence on the southern and northern parts of Georges Bank. In the south, location was a significant factor for predicting the presence of gray meats, highlighting Closed Area I where an outbreak of gray meats occurred after the area reopened to fishing. Yet in the north, reproductive stage was a significant factor, with scallops more likely to have discolored meats after spawning. Study results suggest that gray meats may be a symptom of poor condition that was caused by multiple factors and isolating a single cause may not be possible. Improved screening tests and continued monitoring of scallop health through targeted disease surveys is recommended.

Estimation of the capture efficiency and abundance of Atlantic sea scallops (Placopecten magellanicus) from paired photographic–dredge tows using hierarchical models

The efficiency of survey gear is an important measure that can be used to estimate the absolute scale of populations in assessment models. We develop a general hierarchical model for estimating the efficiency of a New Bedford-style sea scallop (Placopecten magellanicus) survey dredge from paired dredge and Habcam camera system tows. Habcam data for each tow consist of multiple images that give information on within-tow variability of scallop density. The model accounts for these multiple observations as well as the possibility of differences between the true densities in dredge and Habcam pairs due to the pairs not covering exactly the same ground. We fit several models with alternative assumptions to observations on Atlantic sea scallops and compare the relative performance using Akaike’s information criterion. The best performing model estimated higher dredge efficiency on fine substrates than on coarse ones (approximately 0.40 and 0.27, respectively). Our results inform the scale of annual abundance estimates from dredge surveys and reduce uncertainty in the sea scallop stock assessments.

A Comparison of Drop Camera and Diver Survey Methods to Monitor Atlantic Sea Scallops (Placopecten magellanicus) in a Small Fishery Closure

Large-scale fishing closures are a leading tool in the spatial management of global ocean resources. This is exemplified in the U.S. Atlantic sea scallop (Placopecten magellanicus) fishery which uses a rotational scheme of temporary closed areas in both offshore and nearshore waters. The closed areas are generally hundreds to thousands square kilometers, but a group of inshore commercial scallop harvesters were interested in the effect of closing a much smaller area (3 km2), which had sustained valuable harvest before recent poor yields. To describe changes in scallop abundance and size within and around this closure, two independent surveys, a drop camera and diver transect, were conducted through industry–academic collaboration. In addition, this unusual union of a predominately offshore method, the drop camera, and inshore method, divers, was used to better interpret the results of each method. The drop camera survey results suggested that the closure significantly increased the biomass of exploitable scallops, showing that even closure orders of magnitude smaller than commonly used for scallops can be effective. Although the dive survey did not show this, understanding the uncertainties of each method helped resolve this discrepancy. Drop camera densities were calculated from a broader spatial area more representative of the entire area with increased sample size. By contrast, the dive survey provided an intensive description of scallops at each individual survey site. Combining a drop camera survey with dive stations to collect scallop measurements would provide densities from a spatial scale representative of the study area while improving shell height frequency estimation and providing biological data. In addition, this project demonstrated how stakeholder engagement supported by academic institutions and fishery managers can allow intensive monitoring of small fishery closed areas outside of government assessments.

Assessing effects of genetic, environmental, and biotic gradients in species distribution modelling

AbstractTo develop more reliable marine species distribution models (SDMs), we examine how genetic, climatic, and biotic interaction gradients give rise to prediction error in marine SDM. Genetic lineages with distinct ecological requirements spanning genetic gradients have yet to be treated separately in marine SDM, which are often constrained to modeling the potential distribution of one biological unit (e.g. lineage or species) at a time. By comparing SDM performance for the whole species or where observation and predictions were partitioned among geographically discontinuous genetic lineages, we first identified the appropriate biological unit for modeling sea scallop. Prediction errors, in particular contiguous omissions at the northern range margins were effectively halved in genetic lineage SDM (Total error=15%) verses whole species SDM. Remaining SDM prediction error was strongly associated with: i) Sharp climatic gradients (abrupt and persistent spatial shifts in limiting temperatures) found within continental shelf breaks and bottom channels. ii) A biotic gradient in the predation of sea scallop juveniles by the sand star within the Hudson Shelf USA. Our findings highlight how the accuracy of marine SDM is dependent on capturing the appropriate biological unit for modeling (e.g. lineages rather than species) and adequately resolving limiting abiotic and biotic interaction gradients.

Resource Abundance, Fisheries Management, and Fishing Ports: The U.S. Atlantic Sea Scallop Fishery

The Atlantic Sea Scallop fishery has grown tremendously over the past twenty years. The location and magnitude of harvestable biomass fluctuates dramatically due to both natural variation and the explicitly spatial management system designed to allow small individuals to grow larger and more valuable. These fluctuations in natural advantages can have profound effects on fishing ports. We use methods from economic growth literature to show that ports with lower initial scallop landings have grown the fastest. Furthermore, good access to biomass influences long-run changes in landings, although this effect exhibits considerable variability across ports. We also find evidence of returns to scope, suggesting that ports with other fishing activities could be well positioned to attract new scalloping activity when stock conditions are favorable. Further investigation of the largest ports using time-series methods also shows a high degree of variability; there are long-run relationships between scallop fishing and harvestable scallop stock in some ports, short-run relationships in some ports, and no relationship between the two in others. We interpret this as evidence that heterogeneity in the natural productivity of the ocean combined with explicitly spatial fisheries management has induced a spatial component to the port-level response to changes in biomass availability.

Larval Behavior and Protective Implications for Sea Scallops and Surf Clams within the Middle Atlantic Bight: Part One, a Sensitivity Study

In this study, sensitivity studies of larval behaviors were performed, using numerical modeling and analytical methods, for sea scallops (Placopecten magellanicus) and surf clams (Spisula solidissima) in the Middle Atlantic Bight during 2006 and 2010. Based on multiple experiments, a regional ocean modeling system (ROMS) was implemented as the primary physical model, and larval individual behavior models (IBMs) for sea scallops and surf clam larvae were implemented and coupled to the ROMS. To simulate the physical environment and larval behavior using a series of numerical experiments, he coupled ROMS and IBMs were then employed and were driven by realistic dynamic forcing (e.g., winds, tides, and climatological mean boundaries), thermo-dynamic fluxes (e.g., solar radiation, sensible and latent heating), and hydrological forcing for larval behaviors such as vertical swimming and sinking, horizontal drifting with currents, growth, and settlement. Various growth patterns, release types, and larval behavioral parameters were analyzed and are summarized here, based on implications for the protection of sea scallops and surf clam larvae in the Middle Atlantic Bight.

Larval Behavior and Protective Implications for Sea Scallops and Surf Clams within the Middle Atlantic Bight: Part Two, Variability of Physical Environment and Larval Behaviors

Larval growth and settlement rates are important larval behaviors for larval protections. The variability of larval growthsettlement rates and physical conditions for 2006-2012 and in the future with potential climate changes was studied using the coupling ROMS-IMBs, and new temperature and current indexes. Forty-four experimental cases were conducted for larval growth patterns and release mechanisms, showing the spatial, seasonal, annual, and climatic variations of larval growthsettlement rates and physical conditions, demonstrating that the slight different larval temperature-adaption and larval release strategies made difference in larval growth-settlement rates, and displaying that larval growth and settlement rates highly depended upon physical conditions and were vulnerable to climate changes.

Convergence of a Disease and Litigation Leading to Increased Scallop Discard Mortality and Economic Loss in the Georges Bank Fishery

AbstractRotational management in the Atlantic sea scallop Placopecten magellanicus fishery has focused on closing areas to fishing when a high proportion of small scallops is observed in a discrete area, but less attention has been paid to reopening closed areas to prevent poor meat quality. In this fishery there are several large marine protected areas, including Closed Area I of Georges Bank. Intense drop camera surveys of Closed Area I in 1999 led to incorporating a 700‐km2 area into the rotational management scheme. There was a larger abundance of scallops to the south of this area, and these were made available for harvest in 2005, but this fishery was closed in 2006 when the management plan was overturned by a federal court decision. When the area was reopened again in 2011, however, the expected harvest was not achieved. Although fishermen harvested the scallops and opened the shells to extract the meat, they found that many of the meats were gray and not of marketable quality and so they discarded them. The gray meats were linked to a highly pathogenic apicomplexan infection. There was a 52% decline in exploitable biomass between 2011 and 2013 (7,300 metric tons, representing a gross revenue of US$170 million) that could not be attributed to a reduction in landings, resulting in a failure to complete the allotted trips. The scallop rotation management plan has been extremely successful overall, with 69 of the access area trips harvesting over 80% of the allocation; however, increased monitoring of meat quality would further improve management.

Genotoxicity evaluation of oil prepared from the internal organs of the Japanese giant scallop (<i>Patinopecten yessoensis</i>)

Genotoxicity evaluation of oil prepared from the internal organs of the Japanese giant scallop (<i>Patinopecten yessoensis</i>)

Identifiable state‐space models: A case study of the Bay of Fundy sea scallop fishery

AbstractState‐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

Projected impacts of future climate change, ocean acidification, and management on the US Atlantic sea scallop (Placopecten magellanicus) fishery.

Ocean acidification has the potential to significantly impact both aquaculture and wild-caught mollusk fisheries around the world. In this work, we build upon a previously published integrated assessment model of the US Atlantic Sea Scallop (Placopecten magellanicus) fishery to determine the possible future of the fishery under a suite of climate, economic, biological, and management scenarios. We developed a 4x4x4x4 hypercube scenario framework that resulted in 256 possible combinations of future scenarios. The study highlights the potential impacts of ocean acidification and management for a subset of future climate scenarios, with a high CO2 emissions case (RCP8.5) and lower CO2 emissions and climate mitigation case (RCP4.5). Under RCP4.5 and the highest impact and management scenario, ocean acidification has the potential to reduce sea scallop biomass by approximately 13% by the end of century; however, the lesser impact scenarios cause very little change. Under RCP8.5, sea scallop biomass may decline by more than 50% by the end of century, leading to subsequent declines in industry landings and revenue. Management-set catch limits improve the outcomes of the fishery under both climate scenarios, and the addition of a 10% area closure increases future biomass by more than 25% under the highest ocean acidification impacts. However, increased management still does not stop the projected long-term decline of the fishery under ocean acidification scenarios. Given our incomplete understanding of acidification impacts on P. magellanicus, these declines, along with the high value of the industry, suggest population-level effects of acidification should be a clear research priority. Projections described in this manuscript illustrate both the potential impacts of ocean acidification under a business-as-usual and a moderately strong climate-policy scenario. We also illustrate the importance of fisheries management targets in improving the long-term outcome of the P. magellanicus fishery under potential global change.