The Case of the ‘Missing’ Arctic Bivalves and The Walrus: The Biggest [Overlooked] Clam Fishery on the Planet

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 3 106 tonnes y–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 production:biomass ratios comparable to other high-latitude bivalves, a conservative estimate of bivalve standing stock required to support walrus populations is 0.4–3.0 3 107 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 4.0–6.03106 tonnes y–1 of carbonate to buffering of near-surface sediments in Arctic 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

Decadal Trends In Age Structure And Recruitment Patterns Of Ocean Quahogs Arctica Islandica From The Mid-Atlantic Bight In Relation To Water Temperature

Occan quahogs (Arctica islandica) are long-lived bivalves. Distributionl patterns and biology of ocean quahogs ill the Mid-Atlantic Bight (MAB) off the cast coast of North America are directly related to bottom water temperatures. We examined long term recruitment patterns for ocean quahogs across temporal (decadal) and spatial (latitudinal. bathymetric) scales Using a spatially defined (Long Island Sound to Chesapeake Bay mouth) population encompassing a broad size (age) range of animals that had not yet recruited to the commercial fishery [(SL)], An age-at-length relationship for quahogs less than 80 mm SL is described using a power function. Quahog age did not vary significantly with depth or region, nor were any interaction terms between age and length with depth or region significant. An age-length key was developed for ocean quahogs to generate age frequencies for each station. Principal components analysis (PCA) oil the resulting age-frequency distributions standardized per low enabled construction of characteristic age-frequency distributions for similar stations identified by the PCA factor scores. These characteristic age-frequency distributions identified quahog cohorts with modal ages corresponding to recruitment during the 1948-1950. 1954-1959 1972-1980 and 1978-1983 time periods. Observed recruitment patterns in MA B ocean quahogs are strongly related to bottom water temperature patterns. Years it) Which the number of months with water temperatures averaging 6 degrees C to 10 degrees C exceeds the number of months with water temperatures less than 6 degrees C by at least two months are also years that contriute Strongly to the modal year classes in the population age-frequency distributions. In general. years with above average bottom water temperatures during January, February. and March lend to produce year classes that are distinct in the age-frequency distributions front the MAB (quahog populations. The observed time series of quahog recruitment Operates at a different time scale than stock surveys and most estimates of fishery dynamics. The 50-60-y lag between quahog recruitment to the benthos and recruitment to the fishery presents challenges for fishery forecasting in that changes in adult biomass and subsequent effects oil stock-recruit relationships will only become evident oil this this scale

Development Of An Age-Frequency Distribution For Ocean Quahogs (Arctica Islandica) On Georges Bank

Ocean quahogs [Arctica islandica (Linnaeus, 1769)] are the longest-lived, noncolonial animal known today, with a maximum life span exceeding 500 y. Ocean quahogs are a commercially important bivalve, inhabiting the continental shelf of the North Atlantic Basin. Although considerable information exists on the growth and physiology of A. islandica, limited information is available regarding recruitment; accordingly, sustainably managing the fishery is a challenge. To investigate long-termrecruitment trends, the age of ocean quahogs fromGeorges Bank which were fully recruited to the commercial fishery (\u3e80 mm shell length) was determined by analysis of annual growth lines in the hinge plate. Ages of animals representing the fully recruited size range were used to develop an age-length key, enabling reconstruction of the population age frequency. The population age frequency showed that the Georges Bank population experienced an increase in recruitment beginning in the late 1890s. Initial settlement, documented by a few ocean quahogs that were much older, occurred much earlier, in the early 1800s. Following the late 1890s increase in recruitment, the population expanded rapidly reaching carrying capacity in 20-30 y. Recruitment was more or less continuous after this expansion, consistent with maintenance of a population at carrying capacity. Unusually large year classes were not observed, nor were significant periods of high recruitment interspersed with periods of low recruitment. The relationship of growth rate with age for the oldest clams was assessed using the time series of yearly growth increments and the resulting relationship fitted to three models (von Bertalanffy, Gompertz, and Tanaka\u27s ALOG curve). The ALOG model was clearly superior because it allows for persistent indeterminate growth at old age, rather than the asymptotic behavior of the other two and because it allows for a rapid change in growth rate at what is presumed to be maturity

Bivalve Molluscs: Barometers of Climate Change in Arctic Marine Systems

Bivalve mollusks store a complete history of their life in the growth lines in their valves. Through sclerochronology, in combination with isotope signatures, it is possible to reconstruct both post-recruitment growth history at the individual level and commensurate environmental records of temperature and salinity. Growth patterns are integrators of local primary productivity; spatial and temporal changes in growth illustrate commensurate patterns of food availability. Mactrid clams are long-lived, benthic dominant species found on inner continental shelves throughout the Northern Hemisphere where they variously support major fisheries (Spisula solidissima in the Mid-Atlantic Bight, Mactromeris polynyma in eastern Canada, Spisula sachalinensis in Japan) and recreational fisheries (Mactromeris polynyma in Alaska), and serve as dietary items for charismatic species such as bearded seals (Erignathus barbatus) and walrus Odobenus rosmarus divergens). Ongoing studies, employing sophisticated adult growth and larval dispersal models of the response of Spisula solidissima to climate change in the Mid-Atlantic Bight, suggest the general use of mactrids as barometers of climate change over broader geographic footprints. Mactromeris polynyma is a candidate species for shallow arctic marine systems, having a pan-arctic distribution from the Gulf of Maine in the Atlantic to the Bering Sea and Gulf of Alaska in the northern Pacific. The longevity of extant individuals (≤25 years) provides opportunity for detailed reconstruction of the benthic environment and food regimes at the decadal level.https://scholarworks.wm.edu/vimsbooks/1010/thumbnail.jp

Attainability of Accurate Age Frequencies for Ocean Quahogs (Arctica islandica) Using Large Datasets: Protocol, Reader Precision, and Error Assessment

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

The Value of Captains’ Behavioral Choices in the Success of the Surfclam (Spisula solidissima) Fishery on the U.S. Mid-Atlantic Coast: a Model Evaluation

The response of the surfclam Spisula solidissima to warming of the Mid-Atlantic Bight is manifested by recession of the southern and inshore boundary of the clam’s range. This phenomenon has impacted the fishery through the closure of southern ports and the movement of processing capacity north, impacts that may require responsive actions on the part of fishery captains to mitigate a decline in fishery performance otherwise ineluctably accompanying this shift in range. The purpose of this study was to evaluate options in the behavioral repertoire of captains that might provide mitigation. A model capable of simulating a spatially and temporally variable resource harvested by fleets of boats landing in a number of homeports was created. The model includes characterization of each vessel in terms of economics and vessel performance. The model assigns to each vessel a captain with defined behavioral proclivities including the tendency to search, to communicate with other captains, to take advantage of survey data, and to integrate variable lengths of past history performance into the determination of the location of fishing trips. Each captain and vessel operate independently in the simulation providing a spatially and temporally dynamic variability in fishery performance. Simulations showed that a number of behaviors modestly varied performance. Use of survey data and occasional searching tended to increase performance. Reliance on an older catch history tended to reduce performance as did frequent searching. However, in no simulation was this differential large and the differential was little modified by the contraction in the surfclam’s range. Simulations showed that the population dynamics of the clam and the low fishing mortality rate imposed by the Fishery Management Plan permit near optimal fishing performance based on a few simple rules: choose locations to fish that minimize time at sea while permitting the landing of a full vessel load; base this choice on the most recent catch history for the vessel. Simulations suggest that the performance of the fishery is primarily determined by surfclam abundance and the location of patches that control LPUE at small geographic scales. Constraints imposed on fishery performance by port location and vessel size far exceed limitations or ameliorations afforded by modifications in the behavior of captain

Interactive Effects of Climate Change-Induced Range Shifts and Wind Energy Development on Future Economic Conditions of the Atlantic Surfclam Fishery

Rising water temperatures along the northeastern U.S. continental shelf have resulted in an offshore range shift of the Atlantic surfclam Spisula solidissima to waters still occupied by ocean quahogs Arctica islandica. Fishers presently are prohibited from landing both Atlantic surfclams and ocean quahogs in the same catch, thus limiting fishing to locations where the target species can be sorted on deck. Wind energy development on and around the fishing grounds will further restrict the fishery. A spatially explicit model of the Atlantic surfclam fishery (Spatially Explicit Fishery Economics Simulator) has the ability to simulate the consequences of fishery displacement due to wind energy development in combination with fishery and stock dynamics related to the species\u27 overlap with ocean quahogs. Five sets of simulations were run to determine the effect of varying degrees of species overlap due to Atlantic surfclam range shifts in conjunction with fishing constraints due to wind farm development. Simulations tracked changes in relative stock status, fishery performance, and the economic consequences for the fishery. Compared to a business-as-usual scenario, all scenarios with less-restrictive fishing penalties due to species overlap exhibited higher raw catch numbers but also greater reductions in revenue and increases in cost after the implementation of wind farms. This analysis serves to demonstrate the response of the Atlantic surfclam fishery to combined pressures from competing ocean uses and climate change and emphasizes the potential for economic disruption of fisheries as climate change interacts with the evolution of ocean management on the continental shelf

Estimating Sustainable Harvests Of Eastern Oysters, Crassostrea Virginica

Sustainability of a fishery is traditionally and typically considered achieved if the exploited population does not decline in numbers or biomass over time as a result of fishing relative to biological reference point goals. Oysters, however, exhibit atypical population dynamics compared with many other commercial species. The population dynamics often display extreme natural interannual variation in numbers and biomass, and oysters create their own habitat-the reef itself. With the worldwide decline of oyster reef habitat and the oyster fisheries dependent thereon, the maintenance of shell has received renewed attention as essential to population sustainability. We apply a shell budget model to estimate the sustainable catch of oysters on public oyster grounds in Louisiana using no net shell loss as a sustainability reference point. Oyster density and size are obtained from an annual stock assessment. The model simulates oyster growth and mortality, and natural shell loss. Shell mass is increased when oysters die in place, and is diminished when oysters are removed by fishing. The shell budget model has practical applications, such as identifying areas for closure, determining total allowable catch, managing shell planting and reef restoration, and achieving product certification for sustainability. The determination of sustainable yield by shell budget modeling should be broadly applicable to the eastern oyster across its entire range