THE SEDIMENTARY PROCESSES AND GEOMORPHIC HISTORY OF WRECK SHOAL, AN OYSTER REEF OF THE JAMES RIVER, VIRGINIA

Wreck Shoal is a subtidal oyster reef area located in the James River, Virginia. Two significantly different types of oyster reefs are found in adjacent areas on Wreck Shoal. Hard-rock reefs are characterized by a relatively thick oyster shell layer, higher densities of live oysters, a coarser interstitial sediment, and a negligible sediment cover. In contrast, mud-shell reefs are characterized by a very thin osyter shell layer, considerably lower densities of live oysters, a finer interstitial sediment, and a 1-2 cm layer of very fine sediments covering the reef. The contemporary sedimentation processes operating on the hard-rock and mud-shell oyster reefs are distinctly different. The hard-rock oyster reefs are in shallower water, experience stronger bottom currents, and present a hydraulically rougher surface to the flow. The mud-shell oyster reefs are in deeper water, experience weaker bottom currents, and present a hydraulically smoother surface to the flow. These factors result in substantially different bottom shear stresses at the fluid-bed interface. The hard-rock oyster reef, with the high bottom shear stress is rarely depositional with respect to fine sediments. In contrast, the mud-shell oyster reef with the low bottom shear stresses is rarely erosional with respect to fine sediments. The James River estuary has evolved, moving upstream and landward in response to a rising sea level. The Wreck Shoal oyster reefs have developed on the ridge and swale topography of a point-bar formed during the late Pliestocene Epoch. From the 1550\u27s to the 1850\u27s the oyster reef developed vertically almost 1.5 m. From the 1850\u27s to present the oyster reefs have lost more than 1.0 m of elevation due to intense harvesting activity. Conceptual models of subtidal oyster reef dynamics and development are proposed and verified based on field observations. The management implications of the results of the study are presented and recommendations are made for the rational exploitation and management of the resource

Evaluation of a Pound Net Leader Designed to Reduce Sea Turtle Bycatch

Offshore pound net leaders in the southern portion of Chesapeake Bay in Virginia waters were documented to incidentally take protected loggerhead, Caretta caretta, and Kemp’s ridley, Lepidochelys kempii, sea turtles. Because of these losses, NOAA’s National Marine Fisheries Service (NMFS) in 2004 closed the area to offshore pound net leaders annually from 6 May to 15 July and initiated a study of an experimental leader design that replaced the top two-thirds of the traditional mesh panel leader with vertical ropes (0.95 cm) spaced 61 cm apart. This experimental leader was tested on four pound net sites on the eastern shore of Chesapeake Bay in 2004 and 2005. During the 2 trial periods, 21 loggerhead and Kemp’s ridley sea turtles were found interacting with the control leader and 1 leatherback turtle, Dermochelys coriacea, was found interacting with the experimental leader. Results of a negative binomial regression analysis comparing the two leader designs found the experimental leader significantly reduced sea turtle interactions (p=0.03). Finfish were sampled from the pound nets in the study to assess finfish catch performance differences between the two leader designs. Although the conclusions from this element of the experiment are not robust, paired t-test and Wilcoxon signed rank test results determined no significant harvest weight difference between the two leaders. Kolmogorov-Smirnov tests did not reveal any substantive size selectivity differences between the two leaders

Physiological response of scup, stenotomus chrysops, to a simulated trawl capture and escape event

Scup (Stenotomus chrysops) were severely exercised by manual chasing for 6 min, and the clearance of lactate over a 12 hr period was evaluated. Lactate peaked from 0.5 to 1.0 hr following exercise with concentrations ranging from 61.0 to 126.0 mg/dL and returned to rested concentrations within 4 hr post-exercise. Concentrations of lactate in rested fish ranged from 5.2 to approximately 23.0 mg/dL. Fish were observed for 10 days following exercise for delayed mortality. A 100% survival of scup was observed with no significant difference between control and experimental populations. Swimming performance was evaluated for 14.0 to 15.0 cm fork length scup, with a towed stimulus through a still-water circular swimming channel, at prolonged and burst speeds. A maximum sustainable swimming speed of 2.2 BL/sec was observed. Between the speeds of 3.0 and 3.3 BL/sec and 4.4 BL/sec, endurance time significantly decreased with the increase in swimming speed. Blood lactate concentrations were measured at 0.5 and 4.0 hr post exercise, and were used as an indicator of white muscle recruitment. A significant difference was not found between rested and experimental mean lactate concentrations at the maximum sustainable swimming speed of 2.2 BL/sec. White muscle recruitment indicated by increases in lactic acid, was recorded at speeds above the maximum sustained swimming speed, and mean blood lactate concentrations were significantly different within blood sampling times and between swimming speeds. Based on the results of our investigations of lactate recovery in scup following a simulated trawl capture and escape event, we believe that scup interacting with a bottom trawl and subsequently escaping, are physiologically stressed by the event, but recover in less than 6 hr. All experimentally treated fish survived both exhaustive exercise and prolonged swimming, suggesting encounter mortality is minimal. The results of this study do not address the effects of possible physical damage on escape or the effect of multiple encounters

Recent history and response characteristics of Wachapreague Inlet, Virginia : Final report

Wachapreague Inlet, a large downdrift offset inlet in the barrier island complex of the mid-Atlantic coast (Delmarva peninsula), was studied during the period 1971-1974. The inlet channel width is bout 500 m and the throat cross-sectional is about 4,500 m2 • The inlet channel is about 3 km in length, approximately one-half of which is within the well-developed horseshoe shaped ebb delta complex. The maximum channel depth is 20 rn which occurs at the throat. Elements of the study included: (1) the inlet morphornetric history (120 years), (2) assessment of surficial and sub-bottom sediments within the inlet complex, (3) determination of the distribution of tidal flows within the inlet channel, (4) determination of the zone of influence of inlet hydraulic currents along the face of the updrift barrier island and (5) the determination of the response of the channel cross-sectional area to short-term variations in wave activity and tidal prisms. (more...

Bacterial Community Profiling of the Eastern Oyster (\u3cem\u3eCrassostrea virginica\u3c/em\u3e): Comparison of Culture-Dependent and Culture-Independent Outcomes

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 Sorensen’s 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

Effect of size selection within and between fishing gear types on the yield and spawning stock biomass per recruit and yield per unit effort for a cohort of an idealized groundfish

A discrete time model was developed to evaluate yield and spawning stock biomass-per-recruit and yield-per-unit-effort for a cohort of an idealized groundfish. This fish was characterized as relatively long lived (M = 0.2), slow growing (K = 0.2), with maximum length and weight of 100 cm and 10 kg, respectively, and 50% maturity at a relatively early age of 3 years. The size selection characteristics of trawls and hooks were described by a logistic cumulative distribution function (LCDF) with a range of L50 and steepness values. The size selection characteristics of gillnets and traps were described by a scaled normal probability density function (NPDF) with a range of values for Lopt and the standard deviation. Analysis of isopleth diagrams for yield-per-recruit (YPR) and spawning stock biomassper-recruit (SPR) for both types of selection functions indicated that YPR is maximized when harvesting is directed on a fish length slightly larger than that at which biomass for the cohort of the unfished population is maximized, and at fishing mortality rates of 2 and greater. Under these harvesting conditions, SPR was between 24 and 36% of the unfished condition. At these levels of fishing mortality and L50, the steepness of the LCDF does not affect the cohort YPR, but does significantly affect the SPR. Likewise, at these levels of fishing mortality and Lopt, the standard deviation of the NPDF also does not affect the cohort YPR, but does significantly affect the SPR. Thus, a sharper selection process provides a greater SPR available for production of future cohorts. In contrast, yield-per-recruit-per-unit-effort (YPRPUE) is maximized at fishing mortality values of approximately 0.5, when the age at entry or length of susceptibility to fishing gear is set at the age or length of maximum biomass for the unfished cohort. These results present a dilemma for the fishery resource manager: maximize cohort YPR at fishing mortality values of 2 and greater, with a minimum 65% reduction in YPRPUE, or maximize YPRPUE with a 25% reduction in YPR. However, with compromise, 85% of the maximum YPR can be realized with only a 20% reduction of YPRPUE at a fishing mortality level of 0.75

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. © 1988, Estuarine Research Federation. All rights reserved

A Comparative Evaluation of the Habitat Value of Shellfish Aquaculture Gear, Submerged Aquatic Vegetation and a Non-Vegetated Seabed

The habitat value of modified rack and bag, shellfish aquaculture gear (SAG) used for the grow-out phase of the American oyster, Crassostrea virginica, submerged aquatic vegetation (SAV), Zostera marina, and a shallow nonvegetated seabed (NVSB) was comparatively evaluated over a 1-year period in Pt. Judith Pond, a tidal estuary in Southern Rhode Island. Enclosure gear was used to sample the three ecotypes, and organisms (\u3e5 mm) were identified, enumerated, and measured to the nearest millimeter. Abundances of marine organisms and species diversity indices were used as measures of the habitat value of these ecotypes within each season. Environmental and geological parameters were not significantly different between the habitats. Emergent surface area (cm2 m-2 of seabed) within each ecotype was estimated, and used to evaluate its role in providing habitat. The SAG habitat had a significantly greater surface area than either the SAV or NVSB habitats during all seasons. The physical structure of the SAG habitat protects juvenile fish from predators and provides substrate for sessile invertebrates that serve as forage for fish and invertebrates. The SAG habitat supported a significantly higher abundance of organisms per m of seabed throughout the year. Species richness was also significantly greater in the SAG habitat compared with the SAV and NVSB habitats. A 2-way ANOVA indicated significant differences in species diversity (Shannon-Weiner index) between habitats. Tukey’s HSD test indicated that the SAG habitat had significantly higher species diversity than the NVSB habitat, but no significant difference in species diversity was found between the SAG and SAV habitats. These findings indicate that shellfish aquaculture gear provides habitat for many organisms throughout the year, and is especially beneficial to ecosystems that support native species of recreationally and commercially important fish and invertebrates in their early life history stages. Therefore, we conclude that shellfish aquaculture gear has substantially greater habitat value than a shallow nonvegetated seabed, and has habitat value at least equal to and possibly superior to submerged aquatic vegetation

Seabed platform for long-term monitoring in the littoral environment

A seabed installed instrument platform was previously designed and evaluated using scale modeling techniques; and a prototype has now been built and tested in the coastal ocean environment. The purpose of the platform is to provide protection from mobile fishing gear for instruments and other sensors permanently installed in the seabed, and connected to shore via buried submarine telemetry cables. The half-scale prototype unit is constructed of steel reinforced concrete attached to a steel base extension. It is 2.0 m in diameter, protruding 0.6 m above the seabed, and includes a thin steel skirt penetrating 0.6 m into the seabed. The skirt provides additional resistance to lateral displacement caused by forces applied during interactions with mobile fishing gear. The bottom edge of the skirt is equipped with a jetting manifold that allows installation of the unit using low pressure water into unconsolidated littoral sediments of sands and muds. The results of the interaction experiments with commercial inshore trawl nets, scallop dredges and hydraulic clam dredges indicate no displacement of the platform

Growth of the northern quahog, Mercenaria mercenaria, in an experimental-scale upweller

Upwellers have proven to be extremely effective as bivalve nursery units and their use is steadily increasing in North America. The re-analysis of previous work by others suggests an asymptotic relationship between growth (% volume increase per day) and chlorophyll-a effective flow rate (the amount food flowing past a unit biomass of northern quahogs, μg per minute per liter of northern quahog volume). An experiment field study was conducted to define the relationship between food flow and bivalve stocking density. Furthermore, this study was designed to investigate other significant environmental parameters influencing bivalve growth in an experimental-scale upweller system. Northern quahog, Mercenaria mercenaria (Linné), seed were grown from ∼2 (longest axis) to ∼13 mm in an experimental-scale floating upweller from June 21 to August 19, 1999 (four separate experimental periods) in Point Judith Pond, Wakefield, Rhode Island. Flow rates and stocking densities were varied in order to produce a chlorophyll-a effective flow rate range of 360 to 1,500 μg · min-1 · l-1, and growth and environmental parameters were measured semiweekly. During the first two-week experiment (June 21 to July 7) an asymptotic relationship was observed between growth (% increase/day) and chlorophyll-a effective flow rate. A significant difference in growth was found between the treatments. The difference in the functional relationship between experiments 1 and 3 was possibly related to lower DO values, which reduced differential growth in experiment 3. In experiment 1, the low-biomass treatments grew faster than the high-biomass treatments. A significant difference in growth between treatments was also observed in experiment 3, although the asymptotic relationship was less pronounced. In experiment 3, the high-biomass replicates grew faster than the low-biomass replicates. Experiments 1 and 3 both experienced similar environmental conditions; however, experiment 1 encountered higher morning dissolved oxygen (DO) levels. In addition, the within experiment variability in experiment 3 was much less than the variability in experiment 1; therefore, accentuating growth differences in experiment 3. In both experiments 1 and 3 maximum growth occurred near treatment 2 in a range of chlorophyll-a effective flow rates of 550 to 650 μg · min-1 · l-1. In experiments, 2 and 4 there were no significant differences in growth between treatments. Growth appeared to be limited by low oxygen. In order to eliminate the effect of food limitation on growth, the upper third of the replicates (the fastest growing animals) were used to calculate the relative growth rate (RGR) during the two-month experiment. Growth was linearly correlated with morning-dissolved oxygen (R2 = 0.42) and with chlorophyll-a (R2 = 0.35). The critical DO threshold for growth in upwellers appears to be 5 ppm, below which growth is adversely affected. During this study, morning DO levels were less than 50% saturated, indicating the potential for DO levels to be increased. Future research should investigate methods for elevating DO levels in upwellers