Joseph T. DeAlteris

The geomorphic development of wreck shoal, a subtidal oyster reef of the James River, Virginia

Wreck Shoal is a subtidal oyster reef located in the James River estuary, Virginia. This estuary has moved upstream and landward in response to rising sea level. The recent geomorphic history of Wreck Shoal is analyzed based on bathymetric records from the 1850’s to the 1980’s. The data indicate that the shallow oyster reef areas have lost elevation in the last 130 yr. This is attributed to intense harvesting activity during the last century. The late Holocene evolution of Wreck Shoal is developed based on the results of sub-bottom profiles and coring data. These suggest that the Wreck Shoal oyster reef has developed on the ridge and swale topography of a point-bar formed during the late Pleistocene epoch. Contemporary biodeposition processes on Wreck Shoal are evaluated. The results indicate that sediments of biogenic origin (fecal and shell material) potentially accumulate at rates in excess of 50 cm 100 years−1. A model for subtidal oyster reef development is proposed that accounts for sea level rise, biodeposition, and the harvesting activity of man. The model is verified with field observations of reef elevation and radiocarbon dates of oyster shell material. The implications of these results are that oyster reefs should be considered a renewable natural resource, and therefore managed accordingly in concert with the oysters.

A Simulation Study of the Effects of Spatially Complex Population Structure for Gulf of Maine Atlantic Cod

Abstract There is growing evidence that numerous fish stocks consist of several smaller, reproductively isolated units that vary in their ability to produce new recruits each year because of a mismatch with environmental conditions. It has been suggested that spawning aggregations exist for the Gulf of Maine stock of Atlantic cod Gadus morhua and that approximately one-half of the historic aggregations are locally depleted. We developed a spatially explicit, age-based projection model to investigate the effects of complex population structure and spatially variable recruitment on Gulf of Maine Atlantic cod. The results of this study demonstrate that there are significant disparities in the estimates of spawning stock biomass, annual yield, and annual recruitment when a stock with a complex population structure is treated as a single stock. In addition, treating a stock with a complex population structure as a single stock can mask a steady decline in the values of these variables as the spawning aggregati...

Factors affecting hydrodynamic performance of the Nordmøre Grate System: a bycatch reduction device used in the Gulf of Maine shrimp fishery

Abstract Trawl nets used in traditional shrimp fisheries are highly non-selective. While capturing shrimp, trawl nets also retain most other animals, including juveniles of commercially important species, thus depleting stocks. To maximize the efficiency of separation of shrimp from other species in trawl net catches, hydrodynamic experiments were conducted on the Nordmore Grate System, a shrimp bycatch reduction device. The system consisted of two elements, a funnel and a grate; and experimental variables included towing speed, webbing solidity and exit to entrance area ratios for the funnel, and angle of attack, bar diameter, and shape of the grate. Filtration efficiency was inferred from flow disturbance induced by each element, as it was towed in a still water basin. Flow measurements were taken with an electromagnetic current meter at the entrance and at the exit of each funnel and each frame supporting the grates. Water was rejected in the entrance of all funnels with non-porous webbing. Water was ejected from the exit of funnels of intermediate webbing solidity and intermediate exit to entrance area ratio. Water was entrained behind all grates except the 0.32 cm bar diameter grate. Ejection of water at the funnel exit with no rejection at the funnel mouth was attained with 0.08 entrance to exit area ratio covered with 0.4 solidity ratio webbing. Optimum filtration efficiency was observed in the grate with 0.32 cm diameter, round bars placed at a 30 ° angle of attack.

Bacterial Community Profiling of the Eastern Oyster (Crassostrea virginica): Comparison of Culture-Dependent and Culture-Independent Outcomes

ABSTRACT Tissue-associated bacterial community profiles generated using a nested polymerase chain reaction—denaturing gradient gel electrophoresis (DGGE) approach and culture-dependent and culture-independent isolation techniques were compared. Oyster samples were collected from 2 harvest areas along the coast of Maine, in the United States. Profiles from both isolation strategies were evaluated using Sorensens index of similarity and cluster analysis of gel banding patterns. Culture-independent profiles were further evaluated using the Shannon diversity index. In general, the culture-dependent strategy resulted in a greater number of bands within a profile. Bacterial DGGE profiles were found to be highly similar within an isolation strategy, with a higher degree of unrelatedness between culture-dependent and -independent techniques. Cluster analysis identified bands present in the culture-dependent strategy and not the total DNA technique, and vice versa. Significant differences in community profiles between oyster-associated and seawater were observed, indicating a diverse group of specialist bacterial species inhabit and are able to proliferate within the oyster.

Comparison of the Performance of Two Bottom-Sampling Trawls

Abstract The performance of two bottom-sampling trawls was evaluated under various rigging configurations and operating conditions. The trawls examined were a semiballoon shrimp trawl usually towed from a single warp and a high-rise trawl towed from two warps. The geometric performance (i.e., configuration of the trawl while in operation) of the full-scale nets was measured hydroacoustically in the field, and scale models were tested in a tow tank. For the shrimp trawl, wingspread increased significantly with increased bridle length but was not significantly affected by increased speed or current direction. Headrope opening decreased with increased towing speed and bridle length. For the high-rise trawl net, wingspread and headrope opening both decreased with increased speed. In contrast to the clear differences in geometric performance related to net design, rig, and operation, the analyses of catch data from Narragansett Bay, Rhode Island, were not definitive. The high-rise trawl captured significantly ...

Rapid growth of a deep-sea wood-boring bivalve

Abstract The growth of Xylophaga atlantica Richards, a deep-sea wood-boring bivalve, was studied by recovering a 1-year time series of oak and pine panels deployed at depths of 100 and 200 m at the edge of the continental shelf, south of Cape Cod. Change in shell height between samples was used to assess growth rate. At the 100 m site, the first individuals to settle grew much faster, on average, than those that settled later in the year on the same panels (0.085 mm day −1 vs 0.031 mm day −1 , respectively). The growth rate of the maximum sized individuals was 0.027 mm day −1 whereas the modal growth rate was half that at 0.015 mm day −1 . The modal growth rate of those recovered from 200 m was much greater at 0.246 mm day −1 and is thought to be due to the warmer average temperatures there. Differences in growth rate due to season, substrate and previous density were also apparent.

Evaluation of a Large-Mesh Panel to Reduce the Flatfish Bycatch in the Small-Mesh Bottom Trawls Used in the New England Silver Hake Fishery

Abstract Fishermen must use small-mesh bottom trawls to capture certain species of fish that cannot be retained by standard groundfish mesh sizes. These fisheries are subject to bycatch limits when such trawls are used in areas where regulated species reside. Bycatch of regulated flatfish in the small-mesh bottom trawl fishery for silver hake Merluccius bilinearis in the northwestern Atlantic is a concern of management because silver hakes are captured in areas where juvenile regulated flatfish are common. An evaluation of flatfish and silver hake behaviors using low-light underwater cameras suggested that the two species could be separated within the mouth of a bottom trawl. Using the alternate tow method, four different large-mesh panels positioned in the lower belly of the trawl were separately evaluated. One of them proved to be effective in reducing flatfish bycatch while not reducing the catch of silver hakes; a large-mesh panel constructed of 40.6-cm (16-in) stretched mesh that was diamond shaped u...

Quantification of water flow and net drag in midwater trawls

Abstract The flow velocity and hydrodynamic drag of 18 quarter-scale midwater box trawl nets were quantified in a circulating water channel using electromagnetic current meters and strain gauges, with the mouth of each net attached to a rigid pipe frame to maintain geometric similarity. The experimental matrix involved three mesh sizes (25, 50, and 100 mm), three twine diameters (0.5, 1, and 2 mm), two webbing tapers (all bar and three points to one bar), and three test speeds (30, 60, and 90 cm s−1. Under this design, the significant factors affecting the velocity gradient within or ahead of the nets were found to be the solidity ratio of the webbing and the towing speed. The significant factors affecting the drag coefficient of the nets were the solidity ratio and the average webbing angle of incidence. The towing speed was not found to significantly affect the drag coefficient under the experimental conditions.

Effects of trap saturation and species interaction on the capture of Callinectes Spp. crabs in the Guayas Estuary

Abstract Catchability of Callinectes spp. crabs was examined from June through August 1987 in the Guayas Estuary, Ecuador, concentrating on aspects of saturation and interaction effects in traps. Actual versus potential catch due to saturation effects was examined using an experimental design of traps with the catch removed (fished) versus traps with the catch counted but not removed (not-fished). A significant decrease in catch in the not-fished traps was observed after 3 h in the lower estuary and after 21 h in the upper estuary. Experiments to examine intraspecific or interspecific effects on the catchability of the two Callinectes species in traps were conducted in the lower Guayas Estuary using a combination of stocked treatments. Significant differences were observed in the catch of C. toxotes in the treatments with high densities of stocked C. toxotes . The catch of C. arcuatus was not affected by stocking the traps with either species in densities tested.

EFFECTS OF MOBILE BOTTOM FISHING GEAR ON BIODIVERSITY AND HABITAT IN OFFSHORE NEW ENGLAND WATERS

Abstract Mobile fishing gear affects biodiversity and habitat in New England offshore waters through selective fishing activity, seabed disturbance, and discarding and encounter mortality. Selective fishing activity results in geographically localized impacts on habitat and more widespread impacts on biodiversity through the selective removal of specific species with a higher economic value. Seabed disturbance by fishing activity results in physical impacts related to resuspension of fine sediments and scarring of the seabed, chemical effect due to resuspension of nutrients, and biological impacts related to alteration of the benthic community structure. Discards and other benthic fauna that encounter mobile gear and are impacted by the interaction, temporarily alter the ecosystem dynamic. In general, the habitat impacts are restricted to areas of heavy fishing activity, and in shallower water are ameliorated by natural processes that regularly disturb the seabed. Effects on biodiversity are more widespread due to the transient nature of many impacted species. Mobile fishing gear produces approximately 75% of the landings from New England offshore waters. Habitat impact and a loss of biodiversity may be considered a cost of seafood production. Preservation of habitat and biodiversity in marine sanctuaries and reserves is recommended to balance the effects of fishing. This is analogous to societys management strategy in the terrestrial environment.