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Trends in Atlantic surfclam (Spisulu solidissima) population demographic parameters were analyzed using age and length observations obtained from NOAA stock surveys conducted from the 1980s to 2010s in six regions distributed along the Middle Atlantic Bight (MAB) continental shelf. Atlantic surfclam asymptotic length and specific growth rate were estimated for each survey region and decade using the von Bertalanffy growth function. Specific mortality rates were estimated using a linearized negative exponential relationship and the maximum Atlantic surfclam age observed in each survey region for each decade. The estimated Atlantic surfclam mean length in the southern regions of the MAB decreased from 127 to 103 mm, about a 19% decrease, over the four decades. The mean length remained stable at about 130-135 mm in the central survey regions in contrast to the mean length of the Georges Bank Atlantic surfclam population which showed an increase from 101 to 135 mm over the four decades. The asymptotic length estimated for the southernmost survey region declined by 20% and remained relatively constant for the other survey regions over the four decades. Estimated specific growth rates remained unchanged for most of the survey regions, with the overall regional mean decreasing from about 0.25 [y.sup.-1] in the 1980s to 0.20 y~' by the 2010s. Specific mortality rates were not significantly different across the survey regions, although the maximum age estimated for the population in the southern survey region decreased by about 36%. This study provides a quantitative assessment of past and ongoing changes in MAB Atlantic surfclam population demographics that can be used to develop projections of responses to stresses imposed by climate change and commercial fishing. KEY WORDS: Atlantic surfclam Spisulu solidissima, population demographics, growth rale, mortality rate. Middle Atlantic Bight, INTRODUCTION The Middle Atlantic Bight (MAB) region, the portion of the Northwest Atlantic continental shelf from Cape Hatteras to Georges Bank (Fig. 1), is characterized by a productive benthic ecosystem [...]

Oyster population maintenance and growth require a sufficient larval supply competent for metamorphosis and settlement. Larval performance, in terms of growth, development, survival, and metamorphic success, determines the capacity for a larval cohort to effectively settle and establish into an existing population. Exogenous factors influencing larval development include temperature, salinity, food quantity, and food quality. A sufficient diet, composed of balanced protein, lipids, and carbohydrates to meet larval nutritional demands, is required to promote successful metamorphosis. To evaluate the influence of these exogenous factors on oyster settlement potential in Delaware Bay, a well-established biochemically based Crassostrea gigas (Thunberg, 1793) larval model was adapted to simulate Crassostrea virginica (Gmelin, 1791) larval performance under in situ environmental conditions measured during the 2009 to 2011 reproductive seasons at 10 sites across the salinity gradient of Delaware Bay. Variation in the initial egg size and lipid content, and larval food assimilation efficiency was incorporated into the model to represent potential within-cohort phenotypic variability. The middle portion of Delaware Bay along the New Jersey shoreline, bridging the 15-salinity line, generated the most successful larvae each year, whereas the low-salinity reach, on the Delaware side, and Nantuxent Point Reef had more variable success. Survivorship was a function of adequate temperatures and salinities, sufficient food quantity, and favorable food quality defined in part by the protein-to-(lipid-plus-carbohydrate) ratio. Most settlement was predicted by the model to occur between July and September of each year. To validate the model, estimated settlement windows were compared with calculated settlement windows derived from recruitment observations on yearly shell plants. Modeled and recruitment-derived settlement windows agreed well with each other and verified the capacity of the model to accurately forecast in situ larval performance. The oyster larval model, based on measures of lipid, protein, and carbohydrate, successfully passed an important field test, demonstrating the potential of such biochemically based models to reliably evaluate larval performance under real-world conditions. KEY WORDS: Crassostrea virginica, larvae, eastern oyster, performance model, settlement window, biochemical, food, INTRODUCTION Successful oyster population maintenance and growth require a consistent larval supply capable of settlement onto existing beds over time (Coen & Luckenbach 2000, Mann & Powell 2007, Lipcius et [...]

Oyster reefs are a primary source of calcium carbonate in most estuaries and the habitat complexity provided by these reefs supports a diversity of estuarine life. The available surface area of hard substrate on an oyster reef is critical for population maintenance, as this substrate provides habitat for the settlement of new oyster recruits. On natural reefs, the primary substrates available for settlement by spat include live oysters, boxes (dead articulated valves), and cultch (single oyster shells and shell fragments). Data from a long-term oyster monitoring program from February 2016 to October 2020 were used to generate a monthly time series of the percent of total carbonate weight contributed by live oysters, boxes, and cultch at four reefs in the Mississippi Sound. These percentages vary spatially and temporally. When reefs were healthy, live oysters dominated the total carbonate. During the study period, two mass mortality events occurred. Following the 2016 mortality event, the substrate contributing the majority of the carbonate shifted from live oysters to cultch at all reefs sampled. Three reefs exhibited a modest population recovery following the mortality event only to be impacted by a second, more severe mass mortality event in 2019. Boxes usually had the highest number of spat per gram carbonate at all reefs. The potential surface area (PSA) of each substrate type was calculated by comparing the available surface area of each substrate type and the number of spat that settled on each substrate. Correction factors were generated to account for larval settlement preferences and used to either debit or credit the PSA to calculate effective surface areas (ESA) for each substrate type. Cultch offered the highest ESA at Pass Christian, and cultch ESA was higher than box ESA at Henderson Point and Between Bridges reefs. At Bay St. Louis, box ESA was twice that of cultch. These results suggest cultch and boxes are more valuable settlement substrates than live oysters in this region under the conditions present during the survey time frame, which was characterized by low oyster abundance and aperiodic mass mortality. The unbalanced ESA, in which live oyster ESA is underrepresented, represents an unhealthy condition and demonstrates that a critical period exists for reef recovery after mass mortality in which the timely coincidence of increased box ESA and larval availability is essential for rapid recovery from mass mortality. KEY WORDS: Crassostrea, effective surface area, oyster reef, recruitment, mass mortality, population dynamics, recovery, INTRODUCTION The desperate state of the eastern oyster (Crassostrea virginica) over much of its US East- and Gulf-coast range, the accompanying loss of reefal area, and the responding investment into [...]

Organisms increase in size over time (age) due to excess assimilation over metabolic (respiration) energy demands. Most organisms reach a maximum size with increasing age as gain and loss balance. The von Bertalanffy length-at-age relationship, which is commonly used in fishery assessment calculations, imposes such a maximum size. However, some fished species, such as ocean quahogs, Arctica islandica, are long lived and continue to grow at old age. The Tanaka age-at-length relationship has continued growth at old age, but is rarely used in stock assessment models. A modified form of the von Bertalanffy model is presented, which mimics the continued growth at old age of the Tanaka model by allowing the growth parameter (K) to decline with age. This form is suitable for inclusion in stock assessment models based on von Bertalanffy. The proposed model matches Tanaka curves with precision appropriate for the scatter of data used to fit the curves. The observations of ocean quahog length at age and growth rate from New Jersey and Georges Bank demonstrate the ability of the modified von Bertalanffy relationship to represent continued growth at old age for this fished species. Simulated data generated with continued growth at old age were fit with the Stock Synthesis model (SS3). Results comparing traditional and modified growth relationships showed that the original von Bertalanffy model can reasonably approximate modest nonasymptotic growth as long as the number of observations is sufficient to constrain the parameter values. KEY WORDS: Arctica islandica, shellfish fisheries, length-at-age, growth model, ocean quahog, Bertalanffy growth, INTRODUCTION Most organisms increase in size over time in response to excess assimilated energy above metabolic demands, often termed scope for growth (Barilleet al. 1997, Munroeet al. 2013, Sanders et [...]

Warming of the Mid-Atlantic continental shelf has resulted in a range shift of the Atlantic surfclam, Spisula solidissima, north and offshore into waters still occupied by ocean quahogs (Arctica islandica). An ecotone, a boundary transitioning between neighboring ecological systems over a wide range of space and time, now exists over much of the offshore range of the surfclam in which surfclams and ocean quahogs co-occur. Regulations prohibit fishers from landing both species in the same catch, limiting fishing to locations where the target species can be sorted on deck. An at-sea survey sampling 50+ stations in the overlap region was conducted in September 2021 with the purpose of mapping fishable concentrations of surfclams and ocean quahogs. Size frequency and density data of both species were assessed along with environmental parameters. Species overlap between surfclams and ocean quahogs was most prominent in the 40- to 55-m depth range. Density of surfclams shifted within this depth from surfclam dominant in less than 40 m to ocean quahog dominant in greater than 60 m. Atlantic surfclam length increased with increasing summer bottom water temperature, whereas densities remained stable, indicative of proportionately larger but fewer animals in warmer inshore waters. Ocean quahog size metrics and densities, on the other hand, remain relatively unresponsive to temperature and invading Atlantic surfclam populations and instead increase in size with higher latitude. Large ocean quahogs, in particular, exhibit a distinct correlation with high latitude but fail to do so with other environmental variables. This analysis emphasizes the potential for economic disruption of fisheries as climate change pushes surfclams further into the range of the ocean quahog and highlights the need for regulatory changes to allow mixed catches and landings. The study also emphasizes the importance of the relative rates of transgression and regression of range boundaries by abutting faunas in determining the degree of influence of the ecotone between them on the benthic community structure of the continental shelf. KEY WORDS: Spisula solidissima, Arctica islandica, Atlantic surfclam, ocean quahog, range shift, ecotone, climate change, surfclam fishery, range boundary, species interaction, INTRODUCTION The Northwest Atlantic Ocean is a bellwether of climate change, as its warming trends far exceed those observed throughout oceans around the world (Pershing et al. 2015, Kavanaugh et [...]

The ocean quahog, Arclica islandica (Linnaeus 1767), is a commercially important species along the western Atlantic continental shelf. It is a long-lived species, frequently reaching ages over 200 y. Uniquely, it is one of the few bivalves to display sexual dimorphism, in that females grow to sizes larger than those of males. This phenomenon is believed to occur because males reach sexual maturity before females and, thus, have slower growth rates earlier. The growth rates of A. islandica from four sites across the Mid-Atlantic Bight. Georges Bank, Long Island (LI), and north and south of the Hudson Canyon, were measured to determine patterns in growth between males and females. Females begin to outgrow males between the ages of 5 and 15 y at sizes 50-55 mm, though this varies amongst the sites and between decades. Each of the sites is unique in some way. but three sex-dependent growth dynamics are observed. Most commonly, the two sexes diverge in size with females outpacing males in growth rates after the first 5-15 y of life. This outcome occurs at all sites and is generally the most common outcome across decades. In a few cases, female growth rates outpace the males very early in ontogeny. Such cases occur at two sites north of Hudson Canyon, both on the LI continental shelf. Most rarely, the two sexes maintain similar growth rates. This is observed for a few decades at the most southern site. In the population as a whole, these rare outcomes have limited influence on the population so that female-to-male ratio consistently increases with increasing size. This sexually dimorphic growth is not caused by protandry, nor is it compensation for a differential mortality rate between the sexes. Cases where males grow as fast as females may be just as easily indicative of a constraint on female growth as a facilitation on male growth. Egg sizes in A. islandica are larger than those of most other bivalves with planklotrophic larvae. Accordingly, another viable hypothesis is that differential growth is an adaptation to support the large egg sizes in females, where larger female size is essential to counterweigh the consequent reduced fecundity due to larger egg volume. KEY WORDS: ocean quahog, Arclica islandica, sexual dimorphism, Mid-Atlantic Bight, growth rate, INTRODUCTION The ocean quahog (Arctica islandica) is an infaunal, non-colonial species that ranges from Newfoundland, Canada, to Cape Hatteras, NC. USA, and from the Bay of Cadiz in Spain to [...]

Populations of the eastern oyster (Crassostrea virginica) have experienced declines from overfishing and disease throughout much of its US range, though development of maximum sustainable yield (MSY) management criteria has been elusive. This is due in part to the discordance between oyster spawning stock and recruits, as the classic stock- recruitment model does not account for the requirement of shell substrate on which recruits settle. This issue was recently addressed with the development of a surface area-recruitment model, which is herein incorporated into a simulation analysis to estimate MSY-based reference points for C. virginica in the Delaware Bay. Simulations demonstrate that at low natural mortality, fishing mortality (F) may be sustainable at values between 10% and 15%; however, if disease or other mortality-enhancing processes occur, the margin of error in fishing is small and may quickly lead to population and reef collapse, emphasizing a precautionary F < 10%. The MSY-based reference points generated here provide rebuilding goals for the oyster fishery and reef management on fished and unfished reefs and the framework from which shell-planting can be incorporated and optimized in the future. Si les populations d'hurtres americaines (Crassostrea virginica) ont connu des declins dus a la surpeche et aux maladies dans la majeure partie de l'aire de repartition americaine de l'espece, l'elaboration de criteres de gestion bases sur le rendement equilibre maximal (REM) demeure problematique. Cela est du en partie a la discordance entre le stock reproducteur d'hurtres et les recrues, le modele stock-recrutement classique ne tenant pas compte de l'exigence d'un substrat de coquilles pour l'etablissement des recrues. L'elaboration recente d'un modele reliant la superficie au recrutement tente de resoudre ce probleme, et nous integrons ce modele a une analyse de simulation pour estimer des points de reference bases sur le REM pour C. virginica dans la baie du Delaware. Les simulations demontrent que, quand la mortalite naturelle est faible, la mortalite par peche (F) peut etre durable a des valeurs entre 10% et 15%, mais que si des maladies ou d'autres processus qui rehaussent la mortalite ont cours, la marge d'erreur associee a la peche est faible et pourrait rapidement mener a l'effondrement de la population et des recifs, d'ou l'importance, pour une approche prudente, de valeurs de F < 10%. Les points de reference bases sur le REM issus de la presente etude offrent des objectifs de reconstitution pour la peche a l'hurtre et la gestion des recifs exploites et non exploites, ainsi qu'un cadre a partir duquel le depot de coquilles peut etre incorpore et optimise. [Traduit par la Redaction], Introduction The use of biological reference points for sustainable management of commercial fisheries is well ensconced in the management of US federal fisheries, wherein achieving maximum sustainable yield (MSY) is [...]

ABSTRACT Offshore wind energy development on the Mid‐Atlantic Bight (MAB) portion of the Northwestern Atlantic continental shelf could have adverse impacts on the future of the Atlantic surfclam, Spisula solidissima, fishery. The current and potential future areas designated for offshore wind energy development overlap with the present‐day and projected Atlantic surfclam fishing grounds and so could limit the fishery. Fishery impacts imposed by displacement of fishing outside wind farm areas and possible restrictions on vessel transit through the wind farms were simulated using a spatially explicit fishery model. The distribution of catch, hours fished, landings per unit effort (LPUE), time at sea, fishing mortality, and the number of fishing trips were projected for five time periods encompassing the period of 2016–2055. Simulations showed a significant decline in the mean of all fishery metrics (apart from LPUE) as the area of wind farm restrictions increased in scale. Impacts were consistently larger when vessel transit through and fishing within offshore wind areas were prohibited. Impacts were also larger for MAB regions off New Jersey and Delmarva than regions farther north and east. These simulations highlight the necessity of evaluating future conditions as warming temperatures shift the surfclam range relative to the immobile wind farm locations. The offshore wind industry must consider projected long‐term impacts of developmental expansion on surrounding sedentary benthic species and the commercially important fisheries that rely on them. [ABSTRACT FROM AUTHOR]

A sustainable fisheries model for the estimation of harvests of oysters, maintenance of cultch, and restoration of reefs has been applied across the northern Gulf of Mexico. Oyster density and size, and cultch density are provided from surveys by State agencies. The model simulates oyster growth and mortality, and cultch loss. Reef shell mass is increased when oysters die in place and diminished when oysters are removed by fishing. Harvest is estimated as sacks of live oysters that can be removed while retaining reef quality (i.e., reef cultch mass, oyster density). Application of oyster density and cultch density standards (OCS) for fishing at maximum sustained yield shows little sustainable harvest on Public Grounds in the northern Gulf of Mexico. Model heuristics focus discovery of negative and positive feedbacks to reef demise or persistence. Oyster reef dynamics are viewed as persistent processes within negative and positive feedback loops, and occasional shifts between them. A negative feedback loop is set up on poor-quality reefs. Lack of cultch and a paucity of adult oysters diminish recruitment and shell replenishment. In the absence of recruitment, natural shell loss ultimately drives the reef to extinction. A positive feedback loop is set up on reefs with adequate cultch and an abundance of oysters. There, oysters set. survive critical early stages in boxes and reef interstices, reproduce, grow to a large size, and die in place. Harvests on high-quality reefs beyond that which maintains reef cultch and spawning stock, and consequential recruitment failure cause a shift from a positive to a negative feedback loop. Likewise, restricting harvests and planting cultch on poor-quality reefs, together with successful recruitment, promotes a shift from a negative to a positive state. Results of no-net loss of cultch (NNL) and OCS simulations suggest two distinct management approaches. The NNL promotes the sustainability of reef shell and assumes that a stable shell bed promotes a stable living resource, whereas OCS explicitly promotes the sustainability of cultch and stock at msy (maximum-sustainable-yield). Furthermore, OCS, which incorporates optimal reef cultch and oyster density standards, provides restoration benchmarks. Achieving sustainability at msy will simultaneously promote habitat restoration, restoration of ecosystem services, and a sustainable oyster fishery. KEY WORDS: Crassostrea virginica, maximum sustainable yield, reference points, cultch management, fishery management, eastern oyster, INTRODUCTION The eastern oyster Crassostrea virginica, is responsible for creating one of the primary habitat types in the estuaries of the northern Gulf of Mexico. The animal supports a commercial [...]

The implementation of a definitive measure of dredge efficiency for analyzing shellfish survey data substantially improves the estimation of abundance. Commonly, depletion experiments are used to estimate gear efficiency and [...]

Ocean quahogs (Arctica islandica) are the longest lived bivalve on Earth. Individuals on the deep continental shelf off Georges Bank can survive for centuries, and in the colder, boreal waters of Iceland, ages over 500 y can be reached. Ocean quahog landings in the United States represent a $24 million industry, yet assessment models operate with no age data because of the substantial sample size required to develop adequate population age distributions for such a long-lived species, the unknown error associated with age estimates, and the extensive time and financial investment required to create production-scale age datasets. Inclusion of age data for this species requires precision metrics to evaluate aging uncertainty such as percent agreement, percent error, coefficient of variation, and tests of bias. To move forward using error-validated age-composition data, a 3-fold error protocol was developed using a large dual-reader dataset (n = 610) from Georges Bank. First, a proxy age-validation study was performed to corroborate an aging method, followed by error evaluation in the context of age-reader bias, precision, and error frequency. Error thresholds were established for each of the three error methods. Georges Bank samples ranged from 33 to 261 y of age and met the predetermined error thresholds for bias (conditionally because of significant and nonsignificant results), precision (average coefficient of variation less than 7%), and error frequency (less than 10%). Consequently, age estimates were deemed acceptable to support age frequency analyses. Precision and bias error were greatest for the youngest animals and, in the context of age-reader bias, error rates were higher for young male ocean quahogs than for young females. Improved age validation of young, sex-differentiated A. islandica will constrain aging error and guide refinement of both aging and age-error protocols. KEY WORDS: ocean quahog, Aretha islandica, error, precision, bias, age-reader, INTRODUCTION Calcified structures (e.g., fish otoliths, vertebrae, coral skeletons. and bivalve shells) are commonly used to age animals in the marine realm (Hudson 1981, Pentilla & Dery 1988, Richardson 2001). [...]

Shell planting to enhance oyster recruitment and habitat in Delaware Bay, NJ was reinitiated in 2005 with 3 y of federal funding. Since then, annual plantings of locally available surf clam and ocean quahog shell have been funded by the oyster fishery. The cured shell is deployed directly onto sites already containing commercially viable numbers of market-sized oysters in areas that are routinely fished sustainably. The locations targeted to receive shell plants vary and are selected to provide the greatest benefit throughout the fished reef tract. Annual sampling that included shell plants from 2005 through 2017 permitted evaluation of their performance. New oysters set and survive preferentially on newly planted shell during the first season and later at the same level as native shell for at least 10 y so that the benefit of once-added shell is retained for over a decade. Recruitment to shell plants enhances 'good' sets and makes a critical difference during years of 'poor' set. Plant substrate, now with oysters of its own, significantly outperforms native substrate in recruitment and survival of oysters in the second and third years postplanting. with enhancement declining exponentially over the first 4 y. An estimated half-life for this decline is just under 1 y. Beyond 3 y. the plant-based substrate continues to perform at least as well as native substrate. Size-frequency analysis shows that first-year oysters on planted substrate are larger than those on native substrate and that this difference carries through the fourth year of a plant. The volume contributed by live and dead oysters on planted substrate increases over the first 5 y until the contribution to the reef from planted substrate volume matches that of native substrate, thus carrying the enhancement forward through time. Annual survey data from the first 4 y of shell plants show that on seven of eight beds, live plus dead oyster density (number m-2) was up to 2.8 X greater on planted sites than on non-planted sites. Change in density averaged positive over time on both planted and non-planted sites but was greater on planted sites. Shell plants on beds in the Delaware Bay fishery provide 3-4 y of enhanced oyster productivity and continue to double the local native substrate productivity as they age, maintaining an active and productive fishery. KEY WORDS: oyster. Delaware Bay. shell plant, substrates, recruitment, enhancement, fishery, INTRODUCTION Shell planting in Delaware Bay to enhance the oyster Crassostrea virginica (Gmelin) fishery has a long history (Nelson 1889, Moore 1911. Woodward & Waller 1932, Nelson 1959. Ford 1997, [...]

ABSTRACT The Atlantic surfclam, Spisula solidissima, and ocean quahog, Arctica islandica, are biomass dominant bivalve species on the eastern North American continental shelf, both supporting lucrative commercial fisheries in the Mid‐Atlantic with a combined value of about $53.6 million in ex‐vessel revenue per year. The thermal tolerance of Atlantic surfclam is generally below 20 °C, whereas the boreal ocean quahog resides in colder waters maintained by the Mid‐Atlantic Bight Cold Pool. Climate‐induced warming of bottom water temperatures is thought to be linked to the observed distributional shift of the Atlantic surfclam population into waters historically dominated by ocean quahogs. As climate change is expected to continue, this study investigated the future distributions of the two species from years 2016 to 2095 using projected bottom water temperatures and a temperature‐dependent population dynamics model. Simulations show the progressive colonization of Atlantic surfclams offshore into the region earlier occupied by the Cold Pool throughout the 79‐year projection, beginning between the mid‐2040s and mid‐2050s, effectively compressing ocean quahog habitat on all sides. Ocean quahogs are shown to be vulnerable to climate‐induced warming on both the southern, inshore, and offshore portions of the continental shelf, ultimately restricting their habitat by the end of the 21st century to the remaining core of the Cold Pool off Long Island. Atlantic surfclams, however, are likely to be less vulnerable to climate‐induced warming, ultimately increasing their geographic footprint across the MAB. Model projections indicate a large‐scale reorganization event of the continental shelf benthic community structure throughout the remainder of the 21st century. [ABSTRACT FROM AUTHOR]

ABSTRACT The Atlantic surfclam, Spisula solidissima supports a lucrative commercial fishery in the Mid‐Atlantic Bight (MAB) worth roughly $30 million in revenue per year. Rapid climate change is expected to modify the geographic range of the Atlantic surfclam, with consequences for the surfclam fishery. This study evaluated fishery‐based indicators projected from 2020 through 2095 based on anticipated changes in the geographic range and biomass of the Atlantic surfclam, using a Spatially Explicit, agent‐based Fisheries and Economics Simulator (SEFES). Simulations generally showed a positive trend in Atlantic surfclam biomass throughout the next three‐quarters of the 21st century as the clam's range continues to shift offshore and northward along the continental shelf. A general decrease in fishing mortality rate is projected given the present fleet capacity, with a simultaneous increase in catch and landings per unit effort (LPUE), signaling future potential growth in the surfclam fishery. Regionally, forecasts show biomass expanding into deeper waters particularly off New Jersey, Long Island, and southern New England starting in the early 2050s, whereas populations on Georges Bank and off Delmarva gradually decline. Trends in time spent fishing, catch, and LPUE parallel those of biomass in each region. These results can inform managers and business interests that rely on this fishery, as well as other users of the continental shelf, to provide a basis for the development of anticipatory management for the socio‐ecological and economic impacts that may result from future changes in the Atlantic surfclam range and carrying capacity consequent of climate change. [ABSTRACT FROM AUTHOR]

Stock-recruitment relationships (SRR) are used by many resource managers as a metric to evaluate stock reproductive potential and rebuilding capacity when harvested. This relationship is more evident in traditional finfish stock assessment models where larvae are frequently limited by the abundance of spawning adults, whereas invertebrate resources are much more confounding and often do not express a clear spawning SRR. Oysters in particular appear to be limited more strongly by post-settlement mortality as larvae are regularly demonstrated to be present in high abundance in response to timely shell plants; yet unexpectedly, a brood SRR appears to be present. Because of the unique life history of oysters which provide their own habitat through reef accretion, a posit is that the quantity and quality of such habitat are crucial determinants of recruitment to the stock, and habitat quality acts as a surrogate for brood stock in the stock-recruit relationship. An extensive dataset from Delaware Bay with a 65-y time series was analyzed to assess the relationship between available Crassostrea virginica natural reef materials and subsequent spat ( KEY WORDS: Crassostrea virginica, stock-recruitment relationship, shell surface area, salinity, Delaware Bay. substrate preference, INTRODUCTION Stock-recruitment relationships (SRR) are pivotal parameters used in most modern fishery assessments to estimate stock resiliency (Ricker 1954, Beverton & Holt 1957, Paulik 1973, Ricker 1975, Hilborn & Walters [...]

Bivalve molluscs represent a significant proportion of the diet of both Atlantic and Pacific walrus (Odobenus rosmarus rosmarus and Odobenus rosmarus divergens, respectively) and are pivotal to benthic-pelagic coupling and carbonate cycling in the Arctic oceans. The latter is of particular relevance in a period of seasonal ice retreat, freshwater release into associated surface waters, decreasing water pH, and possible undersaturation of Arctic waters with respect to aragonite. Using population estimates and predation rates for the walruses on bivalve molluscs, a conservative estimate of bivalve consumption in the regions of active walruses foraging is 2.0-3.0 * [10.sup.6] tonnes [y.sup.-1]--a tonnage comparable to the landings for the largest U.S. commercial fishery, the walleye pollock fishery in the eastern Bering Sea. Predation loss to other apex predators such as bearded seals is discounted. Using productiombiomass ratios comparable to other high-latitude bivalves, a conservative estimate of bivalve standing stock required to support walrus populations is 0.4-3.0 * [10.sup.7] tonnes. Whereas predominant clam prey species exhibit longevity in the 30+ y range, sampled populations in the Bering and Chukchi seas are dominated by small, often less than 1.0 cm individuals. Large clams are rare to absent in samples, suggesting either rapid turnover of the population with high predation balanced by high recruitment and or a bias in sampling that discounts larger, more sparse individuals. Walrus grazing contributes up to 4.0-6.0 * [10.sup.6] tonnes [y.sup.-1] of carbonate to buffering of near-surface sediments in Artie regions. Accurate estimates of bivalve biomass and, thereby, the carbonate budget of Arctic shelf clam species, are critical to understanding the stability of associated continental shelf communities with continued warming of these high-latitude systems and their associated tendency toward aragonite undersaturation. KEY WORDS: walrus, Odobenus rosmarus divergens, Odobenus rosmarus rosmarus, bivalves, carbonate budget, P:B ratio, THE 'MISSING' MOLLUSCS OF THE ARCTIC: EVIDENCE OF EXISTENCE In Northern Hemisphere estuaries and coastal bays, the carbonate producers are typically oysters (genus Crassostrea, less so Saccostrea and Ostrea) or [...]

The possibility that the economics of the oyster fishery impose a self-limitation on overharvesting has been proffered on occasion. The inefficiency of harvesting by the fishery has been evaluated and estimates of the exploitation rate permissible under conditions of maximum sustainable yield have been obtained in previous studies. The question becomes to what extent does the inefficiency of harvest interact with the economics of the fishery to compromise ready detection of overfishing? This study explores the possibility that the constraint of economics on the fishery occurs at oyster exploitation rates that are higher than maximum sustainable yield, leading ineluctably to overfishing if unconstrained and to the appearance of unduly limited fishing if properly constrained. A model is developed that simulates oyster harvesting by dredging. This model tracks vessel behavior and fishery performance in economic terms (CPUE) under varying stock densities and dredge efficiencies. Simulation results show that stock density and on-deck culling speed have the strongest effect on time required, profitability, and effectiveness of harvest, whereas dredge efficiency has a lesser influence. Evaluation of simulations shows that overfishing occurs at a stock density that provides near-optimal economic returns. The oyster fishery does not perceive a decline in the stock under sustainable conditions, as the on-deck processing capacity enables the catch rate to remain relatively stable until the stock declines well below sustainable levels. The consequence of setting fishing regulations such that a decline in catch is perceived is to assure routine and substantive overfishing, thereby creating a potential conflict between apparent and real sustainability. This conflict may explain the inability of state regulatory authorities to impose limitations consistent with long-term resource stability. The perception that a decline in the rate of catch should be observed under standard effort-based regulatory controls is a principal challenge that must be overcome if sustainability is to become normative in the U.S. oyster fishery. KEY WORDS: oyster, Crassostrea, fishery economics, dredge efficiency, vessel operation, sustainable management, INTRODUCTION Sustainable management of the fishery for the eastern oyster Crassostrea virginica has been elusive. Part of the challenge accrues from the unique necessity of managing the shell bed and [...]

A mass mortality event that occurred in the Mississippi Sound in September 2016 provided an opportunity for the first natural field study of the rate of taphonomic loss of oyster shell. At the Pass Christian Reef, limited recruitment in the years following the mortality event resulted in little shell addition over a 2.67-y period, thereby permitting a direct comparison between shell present as living oysters in August 2016 and dead shell collected in April/May 2019. By April 2019, most oyster shell valves were riddled with holes, some of which perforated the valves. Deterioration of the shell surface was ubiquitous, and edge erosion was commonplace. Left valves were preferentially preserved: the left valves comprised 67% of the intact valves and 85% of the minor fragments after 2.67 y. Thus, at the time of collection, minimally 50% of the right valves originally present on the reef had disappeared. The increased differential between left and right valves of the minor fragments suggests a continuing differential in preservation, leading to cultch being overwhelmingly represented by left valves. Based on estimates derived from changes in shell weight at length and estimates of right-valve loss, by April 2019, between 30% and 51% of the carbonate originally added to the reef in 2016 was lost, yielding an estimated oyster shell half-life of between 2.6 and 5.1 y in the Mississippi Sound. The half-lives estimated from this first infield experiment fall precisely within the range of previous less direct estimates from laboratory experiments or survey time series. Oyster shell degrades rapidly: case histories now include a wide latitudinal range and a wide temperature range, which suggests that these rapid shell degradation rates are the norm over most of the range of the eastern oyster. Understanding the impermanence of oyster shell is crucial to the sustainable management of oyster reefs, as the addition of shell to the reef framework must balance rapid shell degradation rates to prevent stock collapse and ultimately the loss of reef structure. KEY WORDS: taphonomy, shell loss, Crassostrea virginica, Mississippi Sound, INTRODUCTION Carbonate input by bivalve shell formation into marine and estuarine sediments is quantitatively comparable to the production of wood by trees in a forest (Gutierrez et al. 2003). Sedimentary [...]

Common-pool resources such as public oyster grounds are especially vulnerable to overexploitation and habitat loss. Like those elsewhere, oyster populations and habitat of Louisiana public grounds are in decline. To maintain reef habitat and increase oyster abundance, a sustainable harvest model is applied, which allows harvest above that required to maintain reef cultch stasis. The model is restrained to promote shell gain by limiting fishing by area, type (sack versus seed), effort, and season. Harvest quotas and cultch removal rates derived from shell-budget--based modeling are a foundation for sustainable management of public oyster resources. KEY WORDS: common-pool resource, sustainability, fisheries management, oyster, Crassostrea virginica, INTRODUCTION Common-pool resources are especially vulnerable to over-exploitation and habitat loss. Allocation of access and limitation to extractive practices are often ineffective, and common-pool resources typically degrade to a state [...]

Atlantic surfclams support a major commercial fishery in the western North Atlantic Ocean with landings consistently between 15,000 and 25,000 metric tons since 1982. The stock is not and historically has not been overfished nor has overfishing occurred; however, in recent years landings per unit effort have declined. Surfclams are a biomass dominant on the continental shelf and a bellwether of climate change in the northwestern Atlantic. This study investigated the relationship of broodstock and recruitment during a period when Mid-Atlantic warming initiated a shelf-wide shift in the surfclams range. A species distribution function model was used to assess the effective area occupied by surfclams for five study regions (Delmarva, New Jersey, Long Island, Southern New England, and Georges Bank). The effective area occupied by small surfclams was consistently much greater than that for large ([greater than or equal to] 120 mm) surfclams. Three independent statistical analyses of the stock-recruitment relationship found little evidence of a significant association in any of the five regions, suggesting that factors besides spawning stock biomass (SSB) are primary determinants of recruitment success. Interannual variability in recruitment, in part associated with variations in larval transport and in part associated with spatially different rates of mortality post-settlement, is an important source of uncertainty and warming bottom waters driving surfclams into new habitat may decouple any inherent interaction between recruits and SSB. A recruitment index obtained from a fishery-independent survey across the range of the stock, as a consequence, is unlikely to usefully presage changes in abundance of the fishable stock. The wider distribution of settlers relative to the fishable stock, however, positions the species well to respond to changing bottom water temperatures as Mid-Atlantic warming continues.KEY WORDS: ocean warming, clam fishery, effective area, biomass dominant, spawning stock biomass, recruitment index, Spisula solidissima, INTRODUCTIONAtlantic surfclams Spisula solidissima support a major commercial fishery in the western North Atlantic Ocean. Around 20,000 metric tons of surfclam meat were landed in 2015 with landings consistently between [...]