Ian K. Bartol and Roger Mann
Traditional oyster repletion activities have utilized a two-dimensional approach to shell (substrate) deployment to attain maximal coverage in subtidal locations with little consideration for optimal thickness of deployed shell and tidal elevation. Vertical dimensionality may play a vital role, however, in the establishment and persistence of oyster communities. Therefore, a three-dimensional oyster reef was constructed in the Piankatank River, Virginia, and settlement and mortality patterns of oysters were recorded from June of 1993 through September of 1994.
William J. Hargis Jr.
The oyster industries of Virginia and Maryland were based upon adult and juvenile oysters, and their shells, produced naturally on the reefs of the Chesapeake oyster reef system. Without those reefs the billions of bushels of live oysters and shells taken by humans could neither have been produced naturally nor harvested and the valuable social and economic activities derived therefrom would never have occurred.
The origin and development of the formerly massive, naturally self-renewing Chesapeake reef system were directly associated with the evolution of the Bay. Its destruction can be linked primarily to the increase of humans around the Bay and beyond and their demand for oysters and shells. Both phases, development and destruction, of reef history have occurred during the last three-quarters to twothirds of the post-glacial Holocene period, around 7,000 years or less. more...
Walter I. Priest III, Janet Neslerode, and Christopher W. Frye
Dredging can have a beneficial effect on oyster habitat when the placement of the dredged material is effectively managed to help provide the bottom structure necessary to develop an oyster reef. Construction and maintenance of the Waterway on the Coast of Virginia (WCV) by the U. S. Army Corps of Engineers (Corps) has provided a number of examples of this process, both serendipitous and deliberate. The historical development of reefs that evolved from the random overboard placement of dredged material and the subsequent leasing of these areas for oyster cultivation is reviewed. A monitoring plan for the development of a reef in Swash Bay using maintenance dredging material is also described including pre- and post-dredging hydrographic surveys, surface sediment distributions, and shellfish surveys.
After one year, the benthic communities at the recently used placement site, the historical placement site and an unimpacted area in Swash Bay were compared using the Benthic Assessment Method (BAM) to determine short-term impacts. The historical and unimpacted sites had very similar values while the recently used site was somewhat lower. Consequences of continued success in developing oyster reefs in close proximity to a dredged channel are addressed with a suggested management plan that involves rotating the placement among a number of sites. This would allow for the continued maintenance of both the channel and the adjacent oyster reefs.
Carl T. Friedrichs, Bruce A. Armbrust, and H. E. deSwart
Effects of channel geometry on cross sectional variation in along channel velocity in partially stratified estuaries
Carl T. Friedrichs and John M. Hamrick
Analytic solutions for along‐channel velocity through an estuarine cross‐section with laterally varying depth are compared to observations from an array of current meters deployed over a nearly triangular cross‐section of the James River estuary. Analytic results suggest that the transverse structure of along‐channel velocity at this cross‐section is primarily due to simple density‐driven circulation modified by bathymetry. Comparisons of analytic solutions for the amplitude and phase of tidal velocity to observations suggest that linear models which include realistic lateral depth variation should also incorporate across‐channel variation in eddy viscosity. Solutions for various contributions to mean velocity are then derived which incorporate a power‐law dependence of eddy viscosity on local depth. Comparison to observations from the James River suggests that density‐induced circulation is the dominant contribution to along‐channel mean velocity and that riverine discharge also provides a measurable contribution. Nonlinear tides may account for much of the remaining discrepancy between observations and the linear analytic solution. Finally, applications of an existing three‐dimensional numerical model of the James River suggest (i) that inclusion of Coriolis acceleration does not greatly effect the cross‐sectional distribution of along‐channel mean velocity, and (ii) that the form of across‐channel variation in eddy viscosity in the analytic model is consistent with the behavior of the numerical model's more sophisticated turbulence closure scheme.
Carl T. Friedrichs and D. G. Aubrey
Carl T. Friedrichs
Hypsometry is the distribution of horizontal surface area with respect to elevation. Recent observations of tidal flat morphology have correlated convex hypsometry with large tide ranges, long‐term accretion and/or low wave activity. Concave hypsometry, in turn, has been correlated with small tide ranges, long‐term erosion and/or high wave activity. The present study demonstrates that this empirical variation in tidal flat hypsometry is consistent with a simple morphodynamic model which assumes tidal flats to be at equilibrium if maximum bottom shear stress (τ) is spatially uniform. Two general cases are considered: (i) dominance of τ by tidal currents, where τ is equal to maximum tidally‐generated shear stress (τT), and (ii) dominance by wind waves, where τ is equal to maximum wave‐generated shear stress (τW). Analytic solutions indicate that a tidal flat which slopes linearly away from a straight shoreline does not produce a uniform distribution of τT or τW. If the profile is adjusted until either τT or τW is uniform, then domination by tidal currents favors a convex hypsometry, and domination by wind waves favors a concave hypsometry. Equilibrium profiles are also derived for curved shorelines. Results indicate that an embayed shoreline significantly enhances convevity and a lobate shoreline significantly enhances concavity — so much so that the potential effect of shoreline curvature on equilibrium hypsometry is of the same order as the effect of domination by τT or τW.
Economic Aspects Of The Chesapeake Bay Oyster Fishery: Problems And The Future Or Should The Industry Be Revitalized?
James E. Kirkley and Douglas Lipton
Between 1930 and 1939, average annual landings of Crassostrea virginica from Chesapeake Bay was 32 million pounds (meat weight). During the period 1980-88, average annual landings declined to 14.6 million pounds. In 1990, landings declined to less than 3 million pounds of meats. It has been this consistent downward trend in landings, particularly since 1983, that has concerned that National Marine Fisheries Service, various state agencies, and members of the oyster industry. In response to declining harvests, the National Oceanic Atmospheric Administration Sea Grant Program in cooperation with the National Marine Fisheries Service and various state agencies and sea grant programs developed A Plan Addressing the Restoration of the American Oyster Industry. The plan recommends that roughly $3 million annually allocated between 1991 and 1995 for research dedicated to restoring the oyster industry. A proposed $15 million budget raises two important issues that must be addressed: (1) should the industry be revitalized, and (2) if so, what needs to be done. In this paper, we offer that revitalization depends upon the marketability of oysters. A nationwide survey of wholesalers conducted in 1992 suggests that consumer demand for oysters has dramatically declined. Alternatively, oysters may be nearing the end of their product life cycle or going the way of the Edsel, IBM personal computer, or Yugo. Industry revitalization efforts, therefore, must be closely linked to, at least, a generic marketing campaign directed at restoring consumer confidence in oyster products. We conclude, however, that resource enhancement efforts based on bio-remediation goals (enhancing water quality and decreasing the population of jellyfish) may be warranted, and enhancement activities rather than industry revitalization efforts should be the focus of a national research program.
Kenneth A. Moore and Jill L. Goodman
Beds of submerged aquatic vegetation (SAY) may moderate or enhance the standing stocks of dissolved oxygen, nutrients, suspended particulates, and chlorophyll in water masses that are exchanged with adjacent channel areas of the Bay or its tributaries. This study investigated the short-term variability in commonly measured water column parameters at four stations located along a 1 km transect across a polyhaline SAV bed in the lower Bay. Data were collected for 10-day periods during June, August, and October 1993 at 15 min to 3 hr intervals using automated water samplers, arrays of spherical PAR quantum sensors, and Hydrolab datasondes. A similar companion study was conducted at the head of the Bay during these same periods.
Dissolved inorganic oxygen (DIN) and Dissolved inorganic phosphorus (DIP) levels were generally quite low in this polyhaline region of the Bay during most periods ( < lOμM and <1 pM, respectively), however concentrations varied from 1-fold to 10-fold for DIN and 1-fold to 2-fold for DIP at intervals of hours to days. Similar short-term pulses of suspended particles and chlorophyll were also observed. Effects of the SAV meadow on the water column varied with season and the associated meadow development. During June, at maximum SAV biomass, the bed acted to moderate pulses of suspended particles and nutrients, although dissolved oxygen levels varied considerably on a diel basis as a result of the high macrophyte productivity. During August, when bed development was reduced and large amounts of detrital macrophyte production were present, the vegetated shoal appeared to be a source of DIN (especially NH4), and elevated levels of total suspended solids and Chlorophyll and community respiration were evident compared to channelward stations. During October, when secondary regrowth of SAV was observed and detritus was largely gone, SAV and channel areas were most similar.
Evidence For A Relation Between A White Perch Young-Of-The-Year Index And Indices Of Later Life Stages
Thomas C. Mosca III, Herbert M. Austin, and David M. Plotner
Juvenile indices are employed in fisheries management to predict the future abundance of harvestable adults. Frequently, regulations on the utilization of the resource, and a lack of fishery independent abundance data, make verification of the prediction accuracy impossible. In the case of white perch in Virginia, this is not so. Using the weighting system developed for a Chesapeake Bay-wide index of juvenile striped bass abundance based on summertime beach seine data collected in nursery ground waters, we developed a similar index for white perch in the Virginia portion of the Bay. Regressions against Virginia Institute of Marine Science otter trawl survey indices (taken in deep, mesohaline water during winter months) for young-of-the-year (r 2 = 0.719, p = 0.001) and age 1+ (r 2 = 0.666, p = 0.001) white perch were significant and positive. These results lend support for the continued use of juvenile indices for finfish management.
J.P. -Y Maa and C. -H. Lee
Using the VIMS Sea Carousel to conduct in-situ experiments in lower Chesapeake Bay, we found significant spatial a.nd temporal difference of the critical bed shear stress for sediment resuspension, tcr- At the Wolftrap site, tcr varied from 1.1 Pa in the summer to 1.9 Pa in the winter. At the Burwell Bay site, although the bed was too soft for anchoring our research vessel against the changing tide, we identified that tcr was 0.045 Pa. At the Old Plantation site, there was a small amount of fluffy material on top of the bed. At a winter deployment at the Cherrystone site, we found a layer of consolidating fluffy sediment at the surface. Within this layer, there was a transition from fluid mud (without erosion resistance) to bed (with erosion resistance). A typical "type I" behavior of sediment resuspension has been identified at all sites. For this type of behavior, the resuspension rate decreases with time for a given constant bed shear stress larger than tcr. This implies that the erosion resistance increases with depth. The natural sediments behave like cohesive sediments because of the biochemical processes.
Sediment Characteristics And Inorganic Fluxes Associated With Vegetated And Nonvegetated Subtidal Habitats Of The Goodwin Islands, Virginia
Christopher P. Buzelli
The Goodwin Islands Ecosystem is a National Estuarine Research Reserve location and consisting of about 200 ha of intertidal mudflat and marshes surrounded by about 600 ha of vegetated and nonvegetated subtidal habitats extending to the -2.0 m depth contour. It is hypothesized that vegetated subtidal and intertidal habitats are seasonal sources of oxygen and fixed carbon and sinks for inorganic nutrients while sediments represent longer- term carbon storage for the ecosystem as a whole. This study focuses upon subtidal sediment microalgal distribution and biomass, sediment organic and inorganic content, and sediment/water oxygen and nutrient exchange processes in vegetated and nonvegetated habitats. Sediments and microalgae are sampled according to a stratified randomized design and flux measurements are performed on large, intact sediment/water cores. Preliminary analysis of sediment characteristics and microalgal biomass shows great spatial variability over the subtidal environment and seasonal flux studies have supported the source/sink hypothesis. Nonvegetated subtidal habitats appear to contain sufficient sediment microalgal biomass to maintain autotrophic status throughout much of the year. Sampling of subtidal and intertidal sediment characteristics and microalgal biomass will continue during 1994. The results of this study will be compared to simulated sediment stocks and processes derived from a dynamic spatial model of ecosystem primary production being developed for the Goodwin Islands ecosystem.
William J. Hargis Jr. and Dexter S. Haven
The 243,000 acres of Virginia's public oyster reefs (a.k.a. the Baylor Grounds) have been extremely productive of usable and saleable (market .md seed) oysters (Crassostrea virginica), oyster shells and oyster shell by-products. Archaeological remains and historical records show that they have yielded great numbers of whole oysters, oyster meats, oyster "seed" and shell since the 01esapeake was formed some 3,000 years BP. In the last century their natural productivity, as indicated by commercial harvest records (the only long-term data available), has declined markedly. In 1904, Vrrginia's total market (adult) oyster harvest was about 7.6 million bushels (mostly from public grounds). By 1930, roughly a quarter-century later, the haivest from public grounds was some 1 million Va. bu. - somewhat less than a seven-fold decline from the total of 190t By 1957, again about a quarter-century later, the public market oyster harvest was 586,000 Va. bu. - about a ten-fold reduction. This was two years before mortalities attributed to "MSX" were observed in the Chesapeake. Disease did not cause these long-term declines! Neither increasing, but ineffectual, management efforts nor public ostreiculture prevented them The downward trend continues.
Of the 243,000 acres of Virginia's public grounds, 199,000 are in the Chesapeake and its tributary estuaries. During the 1993-94 harvest year, only 5,484 Va. bushels of market oysters were recorded from the reefs in all of those 19,000 acres of public grounds. Of them, 5,173 Va. bushels came from about 3,500 acres of James River "seed" oyster beds above Wreck Shoal. The rest of the Baylor acres in the Chesapeake, some 196,000 acres, produced only 311 bushels. As an economic entity Virginia's public oyster resource outside of the James seems economically defunct and the James is fading fast away.
Hydrodynamical Modeling of a Multiple‐Inlet Estuary/Barrier System: Insight Into Tidal Inlet Formation and Stability
Carl T. Friedrichs, David G. Aubrey, Graham S. Giese, and Paul E. Speer
Two specific questions are addressed concerning the role of tidal hydrodynamics in determining the long‐term morphologic evolution of the Nauset Beach‐Monomoy Island barrier system and the Chatham Harbor‐Pleasant Bay tidal estuary, Massachusetts: (1) why do the barrier and estuary exhibit a long‐term (∼150 yr) cycle of new inlet formation, and (2) once a new inlet forms, why is the resulting multiple inlet system unstable? To address these questions, a branched 1‐d numerical model is used to recreate the basic flow patterns in the tidal estuary at ten‐year intervals during the last half century and also to recreate flow conditions shortly before and shortly after the formation of the new inlet. Results suggest that an inlet will form through Nauset Beach once southerly elongation of the barrier has led to a critical head across the barrier at high tide. If this critical head (enhanced by storm surge and wave set‐up) exists at high tide during consecutive tidal cycles, flood currents can deepen the overwash channel sufficiently to enable the stronger ebb currents to complete the formation process. Once a new inlet has formed, the surface gradient and tidal discharge are drastically reduced along the pre‐existing channel to the south of the inlet. This reduction eliminates the tidal scouring action needed to keep the channel open. Rapid shoaling within the channel to the south of the new inlet completes the hydrodynamic decoupling of the northern and southern sections of the estuary.
Trends in Shark Abundance from 1974 to 1991 for the Chesapeake Bight Region of the U.S. Mid-Atlantic Coast
John A. Musick, Steven Branstetter, and James A. Colvocoresses
Recent stock assessments indicate that the shark stock of the western North Atlantic is exploited at a rate twice the maximum sustainable yield. This finding is supported by data generated by the Virginia Institute of Marine Science longline program for sharks of the. Chesapeake Bay and adjacent coastal waters. Trends in catch per unit of effort since 1974 indicate 60-80% reductions in population size for the common species - sandbar (Carcharhinus plumbeus) , dusky (C. obscurus) , sand tiger (Odontaspis taurus), and tiger (Galeocerdo cuvier) sharks. Declines include numbers of individuals for all species, size classes within species, and in one case a strong decline in relative abundance. Given the limited ability of sharks to increase their population size, these results suggest that stock recovery will probably require decades.
Central Atlantic Coastal Plain - A Summary of the Geological Evolution of Chesapeake Bay, Eastern United States
Steven M. Colman, Jeffrey P. Halka, and C. Hobbs
The seaward margin of the U.S. Atlantic Coastal Plain has fluctuated through time, from near the Fall Line to near the edge of the present Outer Continental Shelf, owing to changes in relative sea level. The strata that underlie the Coastal Plain were deposited in environments that ranged from fully terrestrial to fully marine. Estuarine environments are critical components of the Coastal Plain; they represent the interface, otherwise known as the shoreline, between the marine and terrestrial depositional systems. The Quaternary evolution of estuaries has important implications for both documenting the history of sea-level changes and interpreting ancient coastal-plain strata. In this paper, we briefly summarize the Quaternary history of the Chesapeake Bay, the largest of the many Coastal Plain estuaries on the Atlantic coast. This summary is based on recent syntheses of a wide variety of data (Colman and others, 1988, 1990; Colman and Mixon, 1988) on the history and evolution of the bay.
G. Curtis Roegner and Roger L. Mann
The hard clam is found along the eastern coast of North America from the Gulf of St. Lawrence to Texas. In Chesapeake Bay, the hard clam is restricted to salinities above approximately 12 ppt. An extensive survey of hard clam resources is overdue.
Statements concerning long term trends in populations are not feasible. Hard clams ·grow to a maximum shell length of about 120 mm. There are few documented cases of diseases in wild hard clam populations. Parasitic infestations are also slight. The life cycle of the hard clam includes a pelagic larval phase and a relatively sedentary benthic juvenile and adult phase. In Chesapeake Bay, ripe gametes can be found between May and October, and spawning commences when temperatures rise above 20-23 ·c. The larvae are planktotrophic (feeding). Metamorphosis usually commences at a shell length of 200-210 mm. Predation on new recruits is very high; dense aggregations of hard clams have been found in the absence of predators. Aside from predation and fishing pressure, the natural mortality of larger clams appears very low.
Hard clams are important suspension-feeding infauna, thus they are important in grazing of primary production, transfer of carbon and nitrogen to benthic food chains, and, through excretion, rapid recycling of particulate nitrogen as ammonia. The major food source for hard clams is planktonic microalgae. In Chesapeake Bay, growth occurs in spring and fall, when optimum water temperatures coincide with abundant food.
Clams are capable of living in a variety of sediment types, but higher abundances are found in coarse-grained sediments. Hard clam stocks are susceptible to overfishing. Recruitment rates are poorly understood, as are possible reestablishment periods if areas are depleted through commercial harvesting, and factors influencing larval settlement rates. Hard clam mariculture is well established and could easily be expanded into sites within the Bay. Given the ability of clams to bioaccumulate toxic substances, adequate monitoring should be maintained. The sub lethal effects of toxic material readily found in the lower James River should be examined
Patrick K. Baker and Roger L. Mann
Large populations of soft shell clams persist only in relatively shallow, sandy, mesohaline portions of the Chesapeake Bay. These areas are mostly in Maryland, but also occur in the Rappahannock River, Virginia. In some other portions of the Bay, especially polyhaline portions, low populations of soft shell clams persist subtidally. Restricted populations persist intertidally.
Soft shell clams grow rapidly in the Chesapeake Bay, reaching commercial size in two years or less. They reproduce twice per year, in spring and fall, but probably only fall spawnings are important in maintaining population levels. Major recruitment events do not occur in most years, despite heavy annual sets. Soft shell clams are important food for many predators. Major predators on juveniles include blue crabs, mud crabs, flatworms, mummichogs, and spot. Major predators on adults include blue crabs, eels, and cownose rays. Some other species that may depend heavily on soft shell clams include ducks, geese, swans, muskrats, and raccoons.
Diseases may play an important role in regulating adult populations of soft shell clams; hydrocarbon pollution is linked to increased frequency of disease. Oil pollution does the most widespread and persistent damage to soft shell clams through toxicity, aside from its role in inducing disease. Heavy metals, pesticides, and similar pollutants can be extremely toxic, but the harmful effects to clams do not last if the pollution abates. The main concern with the latter toxicants is bioaccumulation by soft shell clams, with the potential for passing toxic contaminants on to predators or to humans.
Siltation caused by storm events, dredging operations, or erosion, can smother clam populations. Eutrophication, enhanced by nutrient inputs from sewage or agriculture, is not known to have affected soft shell clam populations.
Carl H. Hobbs III
Side-scan sonography of the innermost continental shelf between Cape Henry and the Virginia-North Carolina border depicts a relatively typical inner shelf bottom generally characterized by medium density, meso-scale roughness. Subbottom acoustic protiles depict the stratigraphy as a Tertiary age basement separated from Quatenary-age deposits by a regional, angular(?) unconformity. Holocene-age sediments form a discontinuous layer above another unconformity. The area's topography appears to be a function of the presence of the modern sediments.
Andrew E. Grosz, C. R. Berquist Jr., and C. T. Fischler
Supplies of placer heavy minerals, such as ilmenite, rutile, zircon, and monazite, are anticipated to be in short supply by early in the next century. The depletion of conventional onshore deposits coupled with the declaration of the Exclusive Economic Zone in 1983 have provided the impetus to assess the resource potential of heavy-mineral concentrations in U.S. Continental Shelf sediments as future sources for these mineral commodities.
Mineralogically imprecise assessments of placer resources result from analyses of concentrates derived from small volume samples because of the particle-sparsity effect. The overall low grade of heavy minerals in Atlantic Continental Shelf sediments require the analysis of mineral concentrates from large volumes of bulk sample. A set of procedures to extract and analyze heavy minerals from large-volume samples is presented.
Early Life-History Implications of Selected Carcharhinoid and Lamnoid Sharks of the Northwest Atlantic
The size of most newborn sharks makes them susceptible to predation from their own kind and other large fishes. In the northwestern Atlantic, juvenile nursery grounds can be generally classified according to whether or not the young are exposed to such predatory risk. Several related factors-breeding frequency, litter size, size at birth, early growth rate-may help offset early natural mortality. These factors are counterbalanced by the different species in several different ways, producing numerous early life history strategies. In general, slow growing species are either born at relatively large sizes or use protected nursery grounds, whereas faster growing species tend to rely more on growth rates than the other factors.
C. R. Berquist Jr., C. T. Fischler, L. J. Calliari, and et al
The Virginia Division of Mineral Resources and the Virginia Institute of Marine Science investigated the occurrence of heavy minerals in the offshore sediments of Virginia. We began the project because earlier reconnaissance studies reported high heavy-mineral concentrations from several samples collected off the Eastern Shore of Virginia. Our work confirms the previously reported mineral values and locates additional high concentrations up to 20 nautical miles offshore. Furthermore, we show that potentially economic mineral values are not restricted no surficial sediments, but also are found in the upper 15 to 20 feet of inner continental shelf sediments. Several core samples indicate that potential economic values of heavy minerals are clustered offshore of Hog Island, Smith Island, Virginia Beach, and False Cape. These areas are likely targets for resource assessment studies of heavy minerals and construction or beach nourishment sand. The high heavy-mineral concentrations suggest that further investigations are warranted.
L. J. Calliari, C. T. Fischler, and C. R. Berquist Jr.
The mineral composition of the 3- to 4-phi (0.125 to 0.063 mm) size fraction of 49 surficial grab samples,located north and south of the entrance to Chesapeake Bay and of 38 surficial samples, located in the bay mouth, was determined during this study. Although up to 17 minerals were identified, principal components analysis indicated that seven minerals accounted for 96 percent of the composition variance in the bay samples. By using Q-mode factor analysis, three mineral composition end-members (factors) were selected from the sample data and provided an adequate description of the spatial variation in heavy-mineral composition. The end members suggest possible mineral sources.
Jeffrey P. Halka, Steven M. Colman, and C. Hobbs
The Chesapeake Bay, which is a classic coastal plain estuary, is located on a trailing edge continental margin. It has a surface area of nearly 6,000 km2 and ranges in width from 8 to 48 km. The morphology of the bay clearly reflects its formation as a response to fluctuating sea level during and following the last major continental glaciation. The shoreline is highly irregular, the tributaries form an intricate dendritic drainage pattern, and a deep axial channel occurs along much of its length (fig. 1). Water depths commonly exceed 30m in this deep channel, which is flanked by broad shallow benches. Overall, the bay is quite shallow and has an average depth _of only 8 m. more....
Thomas B. Hoff and John A. Musick
The Mid-Atlantic Fishery Management Council (Council) has primary responsibility for the development ofihe Western North Atlantic Shark Fishery Management Plan (FMP). Currently, there is a consensus among the five East Coast Councils that an FMP for sharks should be prepared. The current concerns focus on many of the same issues that were germane a decade ago when a shark FMP was initiated and then halted mainly because of inadequate information. These issues include 1) an expanded, nondiscriminant, commercial longline fishery ; (2) an existing and rapidly expanding recreational fishery; (3) concern for the extensive waste which occurs from both recreational and commercial activities (especially the rapidly increasing issue of harvesting sharks for the use ofonly fins); (4) the reproductive strategy (few offspring, late maturation , and slow growth rates) of many species; and (5) realization that increased fishing pressure on specific shark species generally results in overfishing. Essential information for stock assessment is lacking for sharks and thus management is severely handicapped. Critical data needs include: valid growth information, stock delineation, documentation of the catch by species, samples of the population size structure, mortality estimates, independent indices of population abundance through time, and documentation of all (U.S. and other nationals) user groups both recreational and commercial . Data are particularly sparse for foreign fisheries which have expanded outside U .S. controlled waters, and which could be harvesting the same stocks of sharks.
Evon P. Ruzecki and William J. Hargis Jr.
Hydraulic model dye test results are examined to provide estimates of nontidal horizontal circulation and movement/retention of oyster larvae in the James River Estuary. Test conditions maintained a constant mean tide and average summer low freshwater discharge. It was assumed that movement of dye in the model would approximate movement of the planktonic (larval) stages of oysters (Crassostroa virginica) in the prototype. Test results were used to rank six dye release points (candidate brood stock locations) with respect to relative quantities of dye retained in areas of the model representing commercially important seed oyster beds during the period 20-40 tidal cycles after release (the time, after spawning, when oyster larvae will permanently attach to a suitable substrate). Under the test conditions, nontidal circulation in the model was similar to that found in a weak partially mixed estuary: upstream motion along the bottom and over the right hand shoals (looking upstream) and downstream motion elsewhere. The pattern was modified by cyclonic motion of surface waters in the upstream and downstream reaches which increased residence time of material in the seed oyster bed region. Greatest retention during the 20-40 tidal cycle period was from releases over upstream and right hand side shoals and is reflected in release point ranking.
Robert J. Huggett
The James River in Virginia was contaminated by the pesticide kepone when the material entered the river as early as 1968 and continued until its discovery in 1975. The river became so contaminated that commercial fisheries were closed. In 1988, 13 years after closure, all fishing restrictions were lifted. The contaminated sediments have been diluted and covered enough by uncontaminated material that the kepone flux back into the water column has diminished. Kepone concentrations in organisms inhabitating the river are finally below the U.S. Environmental Protection Agency and Food and Drug Administration action levels. Biological, chemical, physical and geological aspects of the contamination indicate that remedial actions to remove kepone would be expensive and environmentally unwise.
K. P. Kiley and C. S. Welch
An analysis of non-tidal estuarine circulation and local wind events was conducted employing wind and current records taken along the York River. Three distinct response conditions of non-tidal circulation to wind were observed. These conditions exhibited significant temporal and spatial variability. The first was typified by a positive two layer flow response to wind that was significant in the middle section of the York during the first six days of the study. The second exhibited a positive one layer flow response to wind that was significant in the upper section of the York during the last three days of the study, The third exhibited no statistically significant relation between current patterns and wind. This condition occurred near the mouth of the estuary, and it may indicate that the currents near the mouth respond more substantially to conditions in the adjacent· Chesapeake Bay than to those caused by local winds.
James E. Kirkley
The marine resources of the Chesapeake Bay are believed to provide substantial benefit to residents of the State of Maryland and Virginia. However, the possibility of overfishing and degradation of the marine environment seriously jeopardizes the possible benefit . In thsi section, a brief overview of the economic importance and characteristics of the Chesapeake Bay marine resources is presented. The potential for economic lossee are discussed relative to observed economic values.
The term benthic is derived from the Greek root " benth" which means the depths of the sea. Benthic has then come to mean that which is associated with the bottom of any body of water from lakes to oceans, and encompasses a broad range of organisms from algae to fish. In the Chesapeake Bay there is a wide variety and combination of benthic environments ranging from intertidal flats of sand or mud, shallow seagrass meadows, subtidal bottoms, and deeper channels. These environment take on a unique biological and chemical character, depending upon where they occur along the gradient of Bay salinities and sediment type.
Herbert M. Austin
The value of the marine resources of the Chesapeake Bay is second only to its value as a transportation corridor. The oyster, blue crab and striped bass or rock fish, along with the sailboat, epitomize our vision of the Bay. Nowhere else do such important renewable natural resources co-exist so closely to man's residential and industrial activities.
Over time, all natural resource distribution and abundance fluctuates in response to a normally fluctuating environment. Man's harvest adds an additional pressure, and in some cases recruitment levels cannot keep pace with consumer demand. In the Bay, pollutants, both intentional point source discharge, and unintentional non-point source run-off degrade the estuarine habitat and further reduce reproductive capabilities. Physical modification to the shoreline including bulkheading and filling, and daming of main tributaries such as the Susquehanna or James changes land run-off patterns thereby reducing the detrital energy source, and block spawning runs.
Ronald J. Klauda and Michael E. Bender
Habitat deterioration is consistent with perceived population declines for several resident and anadromous finfish species in Chesapeake Bay that are subjected to different levels of fishing pressure (e.g., striped bass versus blueback herring). Diminution of habitat quality has natural and anthropogenic roots that are difficult to separate. Recent contaminant effects studies focused on Chesapeake Bay fishes can be grouped as follows: (a) mathematical and statistical modeling studies aimed at elucidating contaminant and stock trend relationships using extant data and theoretical insights, (b) biological and chemical field surveys in selected areas to demonstrate spatio-temporal associations between levels of toxic organic and inorganic chemicals and absence or reduction of sensitive species, (c) measurements of condition factors and tissue residues of chemical contaminants in juvenile and older fishes, (d) laboratory studies of life stage and species sensitivities to an array of toxic contaminants, and ( e) in-situ field studies designed to measure the effects of habitat quality on specific life stages of selected species.
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