Investigations into the transport and pathways of scallop larvae—the use of numerical models for managing fish stocks

In a spatial analysis of the Georges Bank sea scallop (Placopecten magellanicus) population, variables of population reproduction and abundance are calculated from Canadian and USA research survey size-frequency data. Using commercial catch as a scaling factor to obtain absolute estimates, the time averages of harvestable-sized population numbers and meat-weight biomass, annual recruit numbers, and egg production were calculated from 1977 to 1988 for five principal subregions of Georges Bank. Average survival from egg to age 2 was obtained directly.

Abundance, growth, and production of the sea scallop Argopecten purpuratus (Lamarck 1819): bases for sustainable exploitation of natural scallop beds in north-central Chile

The role of marine currents in shaping population connectivity in the common cockle Cerastoderma edule was investigated in the southern Irish Sea. C. edule is one of the most valuable and exploited shellfish species in the area, yet very little is known about its population dynamics. In the present study, coupled hydrodynamic and particle tracking models are used in conjunction with genetic data collected at twelve microsatellite loci to estimate the influence of the Celtic Sea front on larval transport between the coasts of Britain and Ireland. Genetic analysis highlights the presence of at least three genetic clusters partitioned within locations, suggesting a contact zone between separate subpopulations. Samples collected from the Irish coast are most similar to each other. On the British coast, the Burry Inlet appears genetically isolated while samples collected from the coast of Pembrokeshire show evidence of connectivity between Britain and Ireland. These results agree with the model’s predictions: away from the coastal zone, residual baroclinic currents develop along tidal mixing fronts and act as conduit systems, transporting larvae great distances. Larvae spawned in south Wales are capable of travelling west towards Ireland due to the Celtic Sea front residual current, confirming the action of the Celtic Sea front on larval transport. Sheltered, flood-dominant estuaries such as the Burry Inlet promote self-recruitment. The validation of the model using genetic data represents progress towards a sustainable future for the common cockle, and paves the way for a more effective approach to management of all Irish Sea shellfisheries.

The patchy spatial distribution of many benthic commercial bivalve species plays an important role in determining the fishing and management strategies applied within a fishery. This study used fisher catch-return data and high resolution Vessel Monitoring System (VMS) data to determine the distribution of fishing effort within a region opened to commercial dredge fishing during the 2003 Tasmanian commercial scallop (Pecten fumatus) fishery, Australia. Fisher catch return data suggested that most (88%) of the open region was fished, however, fine-scale VMS data showed that 50% of the fishing effort occurred within 0.85% of the total area available to fishing, and 95% of the effort occurred within ~12% of the open region. The distribution of VMS inferred that the fishing effort was found to be patchy at all measured spatial scales (5 × 5 km to 250 × 250 m grid cell sizes); however, the degree of patchiness decreased with lower spatial scale cell sizes. Significant differences in the dredged benthic communities recorded within regions exposed to different concentrations of fishing intensity (heavy, moderate and low) were observed, with low and moderately fished regions containing high abundances of screwshells and their associated hermit crabs. Water depth was found to explain some of these observed differences, suggesting that the results may be the consequence of fisher behaviour over pre-existing habitat types. The observed distribution of the fishing effort and scallop beds within the Tasmanian commercial scallop, Pecten fumatus, fishery suits a closed area spatial management strategy, with the areas opened to fishing potentially being of the same scale as scallop beds (km × km).

The use of numerical models for the evaluation of the generating potential of high temperature geothermal fields has increased rapidly in recent years. In the late 1970s and early 1980s there were many papers published on comparisons between the simple lumped-parameter models and the more complex distributed-parameter (numerical) models (e.g., Sorey and Fradkin, 1979; Castanier et al., 1980; Fradkin et al., 1981). These papers generally concluded that in most cases lumped-parameter models give just as reliable estimates as the distributed-parameter models for the potential of geothermal systems. In recent years, however, as more data have been collected from many geothermal reservoirs and the need for very comprehensive evaluations has arisen, the use of numerical models has greatly increased. One advantage of using the more complex numerical models is the fact that they are capable of utilizing most of the relevant field data, such as spatial variability in permeability and porosities, and this capability is very important as field data can help constrain the model.

Presently 80% of the biomass of sea scallop Placopecten magellanicus on Georges Bank is located within 3 large areas closed to fisheries. Sea stars Asterias spp., primary predators of scal- lops, are also aggregated within these closed areas. As prey becomes depleted within one scallop bed, sea stars may move to another food source, possibly to another scallop bed. We tested the hypothesis that sea star aggregations moved from one scallop bed to another within the Nantucket Lightship Closed Area (NLCA) on Georges Bank. We video surveyed 204 stations in the NLCA from 1999 to 2006 using a 1.57 km grid-centric systematic sampling design. The center of sea star abun- dance was calculated by averaging the sea star frequency-weighted latitude and longitude for all stations. Using multivariate analysis of variance and all-pairs comparisons (Hotelling's T 2 ), shifts in the center of sea star abundance were determined by assessing if the locations of the 2 aggregations were different. The sea star center of abundance, standard ellipse and 95% confidence ellipse were superimposed on the scallop density distribution maps to determine the spatial overlap. The distrib- utions of sea star aggregations in the NLCA significantly shifted between consecutive years from 1999 to 2006 and overlapped with areas of high densities of scallops. Shifts in the center of abundance reflect changes in distribution possibly resulting from movement, recruitment and mortality. As sea stars aggregate in these areas presumably due to high abundances of scallops, sea star movement between the scallop beds may increase natural mortality rates of the scallop population on Georges Bank.

This study examines the advection of red snapper Lutjanus campechanus larvae in the northern Gulf of Mexico. The potential for repopulating the eastern Gulf stock through larval transport from the more populous western stock is addressed. Transport pathways across topographic features that inhibit alongshelf flow (e.g., the Mississippi River delta, DeSoto Canyon, and the Apalachicola peninsula) and interregional larval transport are considered. An advective field of currents is developed from a large database of drifter and moored currents, augmented by an operational model to fill gaps. The starting points for larval transport are the locations and day of the year of larval captures from the Southeast Area Monitoring and Assessment Program ichthyoplankton surveys. Because the field of currents is derived from near‐surface observations and the depth distribution of larvae is uncertain, findings are expressed in terms of maximal transport pathways. Transport pathways were principally vectored toward the west during September, October, and May under the influence of relatively strong climatological westward wind stress. Eastward pathways occurred in June, July, and August under the influence of weaker shoreward wind stress. Westward transport pathways past the Mississippi delta were found near the delta, whereas eastward transport pathways were found in deeper waters beyond the continental shelf break, away from typical juvenile settlement habitat. Water movement from east to west across the Apalachicola peninsula occurred in the fall, suggesting the potential for genetic exchange from the eastern to the western Gulf. Eastward water movement across the Apalachicola peninsula occurred in July, but only along the outer shelf.

Fish are adapted to spawn where their larvae will be retained in, or transported to, suitable juvenile habitat. Variability in circulation and behaviour produces variation in larval transport with consequences for recruitment. A biophysical model was used to simulate early larval dispersal of Celtic Sea herring (Clupea harengus) during wintertime in 6 years (2002, 2003, 2004, 2005, 2008, 2010). After 30 days, particles occurred in three areas: inshore Celtic Sea, offshore Celtic Sea, and southern Irish Sea, with the majority (70%–78% on average) of particles retained in the Celtic Sea. Inclusion of tidal forcing increased transport to the Irish Sea and decreased transport offshore, as did release during a spring tide. Retention in the Celtic Sea was increased by diel vertical migration and decreased by horizontal diffusion. Strong and frequent west to southwest winds increased transport offshore, while strong and frequent east to south-southeast winds increased inshore retention in the Celtic Sea and transport into the Irish Sea. The study shows how tides, winds, and behaviour influence larval transport and retention and highlights potential impacts of climate change on population persistence.

Aim: To examine the numerical modeling of seawater intrusion and show its implication for sustainable coastal acquifer management. Problem Statement: The global rise in the world population has necessitated the essentiality of water which also has linkage with power and agriculture. However, arid and semi-arid regions occupy almost one-third of the global land surface which makes many regions to be under harsh and rising water stress. The intrusion of seawater into some sections of aquifers has been one of the major problems contributing to water scarcity, especially during the dry season. Significance of Study: A numerical model is a reasonably accurate and economical tool to simulate and predict the head and quality of groundwater in coastal aquifers if it is properly calibrated using the available measurements of heads, pumping rates, and boundary conditions. The calibrated geo-hydrological parameters can then be used to validate the model for another set of measured data. Thus, it is imperative to predict seawater intrusion into coastal aquifer using numerical modeling tools for water management and sustainability purpose. Methodology: This review article was compiled using references from previous literatures addressing seawater intrusion into coastal aquifer. Cited cases were referenced from different relevant journals. Discussion: This article has presented the fundamental principles and mechanisms of seawater intrusion into coastal aquifer. It was observed that seawater intrusion may arise as a result of moderately lower groundwater withdrawal in dry seasons during which the intrusion of seawater is considerably much when compared with the rainy season. The major influencing factors are temperature, rainfall, abstraction rate and evaporation. However, abstraction rate is the most vital variable in relation to rise in population because the saline water migrates more inland due to water over-extraction from the subsurface without adequate replenishment in either semi-arid or arid regions. Different applicable mathematical models for seawater intrusion into coastal aquifer stated in this review are visual MODFLOW, MT3DMS routines, SEAWAT-2000 routines and FEFLOW routines. The applications of these models in the numerical modeling of coastal aquifers in some countries are stated and with their respective influence on the objectives of the study and the results obtained. Conclusion: In conclusion, the use of numerical modeling in studying the nature of seawater intrusion is imperative to achieve sustainable coastal aquifer management.

Smith, S. J., Black, J., Todd, B. J., Kostylev, V. E. and Lundy, M. J. 2009. The impact of commercial fishing on the determination of habitat associations for sea scallops (Placopecten magellanicus, Gmelin). – ICES Journal of Marine Science, 66: 2043–2051. The sea scallop (Placopecten magellanicus) population off southwestern Nova Scotia in Scallop Fishing Area 29 has been monitored by an annual drag survey since the fishery started there in 2001. A new stratification scheme based on surficial geology maps from a multibeam bottom mapping and geology ground-truth project completed in 2004 in the area have been used for survey design since 2005. Survey data from before 2005 have been post-stratified using the new strata. The efficiency of the design with respect to variance reduction appears to have diminished over time suggesting that the association between scallop abundance and bottom type may not have been as strong or constant as first assumed. Modelling of the association between scallop abundance and bottom type and depth using a Bayesian hierarchical approach confirms this diminishing relationship. Comparison of the results from the model with spatial measures of fishing effort based on satellite vessel monitoring data suggests that increasing exploitation may be masking the relationships as scallop beds are targeted and fished down. These results could have implications on the interpretation of species habitat associations from areas where data are only available from periods when the populations have been exploited over a long time. In these cases, the spatial distribution of fishing effort may be a better indicator of species habitat associations than the estimates from surveys.

Larval transport is fundamental to several ecological processes, yet it remains unresolved for the majority of systems. We define larval transport, and describe its components, namely, larval behavior and the physical transport mechanisms accounting for advection, diffusion, and their variability. We then discuss other relevant processes in larval transport, including swimming proficiency, larval duration, accumulation in propagating features, episodic larval transport, and patchiness and spatial variability in larval abundance. We address challenges and recent approaches associated with understanding larval transport, including autonomous sampling, imaging, -omics, and the exponential growth in the use of poorly tested numerical simulation models to examine larval transport and population connectivity. Thus, we discuss the promises and pitfalls of numerical modeling, concluding with recommendations on moving forward, including a need for more process-oriented understanding of the mechanisms of larval transport and the use of emergent technologies.

Effects and mitigations of ocean acidification on wild and aquaculture scallop and prawn fisheries in Queensland, Australia

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.

A decision-theoretical approach was used to evaluate strategies to rebuild a severely depleted scallop (Pecten novaezelandiae) populations in the Tasman Bay and Golden Bay of New Zealand. These strategies were: no intervention, cessation of seabed bottom contact fishing, and reduction of sediment and nutrient runoff from surrounding land through on-farm practices. Our approach combined outputs of estimated effects of on-farm practices on erosion and nutrient reduction with a stochastic dynamic model of the scallop populations. The most effective individual intervention is eliminating bottom contact fishing through dredging and trawling which increased scallop biomass on average by 73% compared to the no intervention scenario. Although on-farm practices have reduced sedimentation and nutrient runoff significantly (28–36% and 2%, respectively), they have no effect on scallop biomass if implemented individually and led to only marginal improvements in scallop biomass if implemented alongside cessation of bottom contact fishing (2–4%). Although our results showed, on average, substantial recovery in the scallop population when reducing seabed bottom contact and water pollution, the large uncertainty boundaries makes it unclear whether these improvements would be realized. The long-term success of such strategies will depend on the available habitat being able to sustain high densities of healthy scallop adults and recruits, a situation that has been posited in our analysis. Where scallop juvenile survival is compromised by sedimentation, nutrient pollution, or other exogenous influences, proposed interventions may be insufficient to aid recovery.

Ecological conceptual models: a framework and case study on ecosystem management for South Florida sustainability