David E. Krantz, C. Hobbs, and Geoffrey L. Wikel
The continental margin of Virginia, and of North America more broadly, is the physical transition from the high elevation of the continent to the low of the ocean basin. This transition was created as rifting pulled apart the ancient supercontinent Pangaea to create the Atlantic Ocean basin. Tectonic forces fractured and stretched the bedrock to create a stair-step ramp that subsequently would be mantled with sediment built up by erosion and transport off the continent.
The Coastal Plain and Continental Shelf of Virginia are contiguous and discrete physiographic provinces of the continental margin delimited by the present elevation of sea level. On geologic time scales of thousands to millions of years, the coastal zone—the boundary between the coastal plain and shelf—is dynamic and migrates hundreds of kilometers landward and seaward. Today, the Atlantic shore of Virginia lies just past halfway across the margin: about 150 km (93 mi) from the edge of the Piedmont at the Fall Zone, and about 100 km (62 mi) from the seaward edge of the shelf (Figure 1). The modern coastal zone occupies nearly the same position as during several previous interglacial highstands of sea level that have recurred at approximately 100,000-year (abbreviated 100 ky, for “kilo year”) intervals since the middle Pleistocene (about the last 750 ky). more ...
Roger Mann, Daphne M. Munroe, Eric N. Powell, Eileen E. Hoffmann, and John M. Klinck
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.
Ryan W. Schloesser, Mary C. Fabrizio, Robert J. Latour, Greg C. Garman, Bob Greenlee, Mary Groves, and James Gartland
Rapid increase in abundance and expanded distribution of introduced blue catfish Ictalurus furcatus populations in the Chesapeake Bay watershed have raised regional management concerns. This study uses information from multiple surveys to examine expansion of blue catfish populations and document their role in tidal river communities. Originally stocked in the James, York, and Rappahannock River systems for development of commercial and recreational fisheries, blue catfish have now been documented in adjacent rivers and have expanded their within-river distribution to oligo- and mesohaline environments. Range expansions coincided with periods of peak abundance in 1996 and 2003 and with the concurrent decline in abundance of native white catfish I. catus. Blue catfish in these systems use a diverse prey base; various amphipod species typically dominate the diet of smaller individuals ([FL]), and fishes are common prey for larger blue catfish (>300 mm FL). Recent studies based on stable isotope analyses suggest that adult blue catfish in these systems are apex predators that feed extensively on important fishery resources, including anadromous shads and herrings Alosa spp. and juvenile Atlantic menhaden Brevoortia tyrannus. Minimizing effects on Chesapeake Bay communities by controlling high densities of blue catfish populations is a primary goal of management, but conflicting demands of the commercial and recreational sectors must be resolved. Further, low market demand and human consumption concerns associated with purported accumulation of contaminants in blue catfish pose additional complications for regulating these fisheries.
Six Fish and 600,000 Thirsty Folks—A Fishing Moratorium on American Shad Thwarts a Controversial Municipal Reservoir Project in Virginia, USA
J. E. Olney, Donna M. Bilkovic, Carl Hershner, Lyle M. Varnell, Harry V. Wang, and Roger L. Mann
Moratoria on fishing directly impact fishers, distributors and marketers of product and can have serious socio-economic implications. Moratoria can impact communities but usually populations closely linked to the banned activity. In an unprecedented example, a moratorium on fishing in Virginia has directly impacted a nonfishing citizenry by thwarting plans for a public utility. In May 2003, a panel empowered to regulate marine resources denied permission to withdraw raw water from a pristine freshwater river, the Mattaponi. The controversial action spoiled a multi-million dollar plan to establish the King William Reservoir, a water source considered essential to future growth and development in the region. The facility was designed to serve a projected 600,000 people in 2040 but the Mattaponi Indians, environmentalists, local citizens and commercial fishers opposed the plan. A central issue was conservation of American shad Alosa sapidissima, an anadromous clupeid native to the U.S. east coast. An inriver moratorium on fishing for American shad imposed in 1994 remains in effect. In the reservoir debate, scientists advised the panel that the project would withdraw water in the center of the larval nursery area for this species and in a river that accounted for the highest statewide production of juveniles. Scientists recommended relocating the intake since losses of larvae to withdrawal could be counter to restoration goals of the moratorium. Using quantitative models, municipal authorities argued that only six American shad would be lost annually to impingement or entrainment. The panel rejected this argument and proposals to mitigate losses.
Wolfgang K. Vogelbein, John M. Hoenig, and David T. Gauthier
Striped bass (Morone saxatilis) in Chesapeake Bay, USA, are currently experiencing an epizootic of mycobacteriosis. Visceral disease prevalence in resident fish exceeds 50% and prevalence of skin ulcers can exceed 30% in some areas. Two primary hypotheses regarding emergence of this chronic bacterial disease propose that anthropogenic stressors constitute important underlying modulating factors
Epizootiology of mycobacteriosis in Chesapeake Bay striped bass (Morone saxatilis): Large-scale field survey
David T. Gauthier, Robert Latour, and Wolfgang Vogelbein
Striped bass in Virginia and Maryland waters of Chesapeake Bay are experiencing an ongoing epizootic of mycobacteriosis. Visceral disease prevalence exceeding 50% has been reported in several locations by various authors, and skin lesion prevalence exceeding 30% has been observed. The high prevalence of skin lesions observed in Chesapeake Bay striped bass is unusual and has not, to our knowledge, been reported previously in wild fishes.
Christopher A. Ottinger, J. Jed Brown, et al, Martha Rhodes, Howard Kator, David T. Gauthier, and Wolfgang K. Vogelbein
Much of what is known of mycobacteriosis in wild striped bass from the mid-Atlantic region of the United States is based on our observations from Chesapeake Bay and its tributaries, where high infection prevalence and lesioned fish are frequently observed. Comparatively, the occurrence and severity of mycobacteriosis in striped bass from watersheds adjacent to Chesapeake Bay are relatively unknown. This study represents the first report on mycobacterial infection in striped bass harvested from two sites in Delaware Bay.
The ecology of mycobacteria infecting striped bass (Morone saxatilis) in Chesapeake Bay: A research plan
Howard Kator, Martha Rhodes, and David Gauthier
The ecology of mycobacteria in estuarine and marine waters remains poorly understood. The current epizootic in Chesapeake Bay striped bass and newly described pathogens Mycobacterium shottsii and M. pseudoshottsii raise ecological questions that if answered can improve our understanding of the pathogenesis of mycobacteriosis in this fish species.
An Unprecedented Scientific Community Response to an Unprecedented Event: Tropical Storm Agnes and the Chesapeake Bay
M. P. Lynch
In June 1972, the remnants of Hurricane Agnes brought destructive floods to the watershed of the Chesapeake Bay basin. Unlike Hurricane Isabel, Agnes did not strike Chesapeake Bay directly, but deposited a record amount of rainfall on the watershed. The evening that the Agnes rainfall began in earnest coincided with a meeting of the Citizens Program for the Chesapeake Bay. The directors of the three largest Chesapeake Bay research institutions, Drs. Donald W. Pritchard, L. Eugene Cronin, and William J. Hargis Jr., were in attendance at this meeting. The potential magnitude of the Agnes rainfall was readily apparent at the meeting as one of the planned evening events had to be moved due to a foot of water in the meeting room. The following morning at breakfast, the three directors committed their institutions to “Operation Agnes,” extensive studies of the biological, chemical, and physical impacts of this event. Hargis, Cronin, and Pritchard were good friends and strong competitors of long standing. Since 1949, Pritchard had been the first full-time director of the Chesapeake Bay Institute (CBI); Cronin had headed the Chesapeake Biological Laboratory (CBL) since 1951; and Hargis had been director of the Virginia Institute of Marine Science (VIMS) (and its predecessor the Virginia Fisheries Laboratory-VFL) since 1959. In 1964, the three directors had set up an informal Chesapeake Bay Research Council (CBRC) to coordinate some of their Chesapeake Bay research activities. They used the CBRC mechanism to coordinate “Operation Agnes,” a commitment that was made without any assurance of financial support for these studies. The gamble taken by the three laboratory directors was successful, eventually resulting in a peer-reviewed book published by The Johns Hopkins University Press entitled The Effects of Tropical Storm Agnes on the Chesapeake Bay Estuarine System. Operation Agnes was the last project undertaken by the CBRC. Reorganization by two of the parent institutions and incorporation of the Chesapeake Research Consortium (CRC) resulted in a realignment of Chesapeake Bay scientific leadership and the leadership of Operation Agnes moved from CBRC to CRC. The scientific community’s response to Tropical Storm Agnes—an unprecedented event— was in itself unprecedented. A number of coincidences came into play: recent (1969) experience with flooding from Hurricane Camille; fortuitous attendance of the leaders of the three largest Chesapeake Bay research institutions at a meeting directly affected by Agnes; and the prior mobilization of the three institutions to conduct extensive hydrographic studies throughout Chesapeake Bay. The most important factor, however, was the strong commitment of three laboratory directors to the understanding of the Chesapeake Bay system.
M. M. Montane and H. M. Austin
Few studies have focused on the effects of climatic perturbations, such as hurricanes, on finfish recruitment and behavior. The Virginia Institute of Marine Science (VIMS) Trawl Survey has sampled continuously throughout the Virginia portion of Chesapeake Bay for 50 years. While hurricanes have impacted Chesapeake Bay during this time, three periods of hurricane activity— September and November 1985 (hurricanes Gloria and Juan), September 1989 (Hurricane Hugo), and September 2003 (Hurricane Isabel)—coincided with the largest spikes in juvenile recruitment of Atlantic croaker (Micropogonias undulatus) for half a century. The fall (October–December) croaker young-of-year indices for 1985, 1989, and 2003 were seven, five, and eight times greater, respectively, than the 50-year average. Typically Atlantic croaker display great interannual variability in Chesapeake Bay, with these fluctuations shown to be weather related. The timing of Atlantic croaker recruitment to Chesapeake Bay is such that late summer/fall hurricanes are most likely to affect them, as opposed to other shelf spawners. Understanding the effects of hurricanes on species, such as croaker, that have enormous ecological, commercial, and recreational importance is essential for prudent fisheries management.
W. G. Reay and Ken Moore
Water quality impacts from Tropical Cyclone Isabel on the York River estuary were assessed based on long-term, near-continuous, shallowwater monitoring stations along the York River proper (poly- and mesohaline regimes) and its two tidal tributaries—the Mattaponi and Pamunkey rivers (oligohaline and tidal freshwater regimes). Regional rainfall from 18 to 19 September 2003 ranged from 5.8 to 11.7 cm. Peak mean daily stream flow occurred on 21 September 2003 and represented a 20- and 30-fold increase over prestorm conditions on the Mattaponi and Pamunkey rivers, respectively. Isabel produced a storm surge of 1.7 m near the mouth of the estuary and 2.0 m in the upper tidal freshwater regions. The tidal surge resulted in a short-term (12- to 36-hour) pulse of high salinity water (approximately 10 ppt greater than pre-storm conditions) within the oligohaline portion of the estuary. In comparison, salinity levels within the upper tidal fresh water and down-river poly-and mesohaline regions remained relatively unchanged. Following the storm surge, salinity levels within lower portions of the estuary declined 1.5 to 4.5 ppt for an extended period in response to freshwater runoff. Elevated turbidity—in some cases extreme—was in direct response to the storm surge and waves associated with Tropical Cyclone Isabel. With the exception of a single station, maximum storm-associated turbidity levels varied between 192 and >1000 NTUs (nephelometric turbidity units). Turbidity levels returned to prestorm conditions within a 24- to 30-hour period at most stations. Perhaps the most significant environmental impact associated with the passage of Isabel was the persistent low dissolved oxygen (DO) levels (3–4 mg⋅L-1) that occurred at the tidal freshwater stations. Low DO at these stations coincided with increased freshwater inflow to the Mattaponi and Pamunkey rivers, suggesting augmented loadings of readily degradable organic material from the watershed. Mean daily DO levels took approximately two weeks to return to prestorm levels at these sites. Dissolved oxygen levels at the poly- and mesohaline stations within the York River proper remained at or above 5 mg⋅L-1 prior to, during, and after the storm’s passage.
John A. Musick
This publication describes the scientific principles and techniques used for resource management of elasrnobranch fisheries with emphasis on the particular context of elasmobranchs. The management characteristics of these fishes are described - their common bycatch character and their biological constraints on productivity (low growth rate, late maturity and Tow fecundity). Stock assessment of elasrnobranchs is described in the context of rnanagement objectives in a wide management context. Special attention is given to accurate species identification given the prevalent aggregating of landings data across species, genera and often families in this group. Techniques and experiences for tagging elasmobranchs for population estimation are described as well as methods of genetic techniques for stock identification. Methods and problems involved in determining ,age, growth, fecundity and mortality rates are described and their use in age-structured models Within the context of the reproductive biology of these fishes. Demographic models to determine the productive of elasmobranch resources are described, Use of surveys to,complement information derived from fisheries is described together with management measures, Last, practices of shark utilization are noted.
J. D. Boon
Tidal conditions fail to explain a paradoxical similarity in water level extremes induced by Hurricane Isabel on 18 September 2003, and the 23 August 1933 storm of record at Hampton Roads, Virginia. Storm surge peaks occurred near astronomical high tide during both storms, but Isabel arrived during neap tides while tides during the 1933 storm were nearer to spring. In addition, Isabel produced a lesser storm surge, yet she yielded a storm tide, or high-water mark, roughly equal to that of the 1933 hurricane. The answer to the paradox lies in observed sea level—water level measured relative to the land—and its movement during the 70 years between these events. Water level analysis shows that the sea level change observed can be divided into three categories at three different time scales: daily (astronomical tides), monthly (seasonal change), and yearly (secular trend in sea level). At Hampton Roads, a secular rise rate of 4.25 mm⋅yr-1 (1.39 ft/century) predicted an increase of 29.8 cm in 70 years; mean sea level for the month of September stood an additional 21.9 cm above the annual mean for 2003. These numbers are comparable to the mean semirange of tide (37.0 cm) at Hampton Roads. Thus seasonal and secular change are both factors of key importance in evaluating storm tide risk at time scales attributable to major hurricanes (100 years). Adoption of a new vertical reference, projected monthly mean sea level, is proposed to facilitate their inclusion in storm tide predictions at decadal time scales.
Colin A. Simpfendorfer, Ramon Bonfil, and Robert J. Latour
Mortality is an essential parameter in understanding the dynamics of any population and sharks are no exception. Without knowledge of how fast individuals are removed from a population it is impossible to model the population dynamics or estimate sustainable rates of exploitation or other useful management parameters.
L. H. Brasseur, A. C. Trembanis, J. M. Brubaker, and Carl T. Friedrichs
After making landfall on the North Carolina coast on the morning of 18 September 2003, Category 2 Hurricane Isabel tracked northward parallel to and slightly west of the Chesapeake Bay. At Gloucester Point, near the mouth of the York River estuary, strong onshore winds with speeds in excess of 20 m⋅s-1 persisted for over 12 hours and peak winds reached over 40 m⋅s-1, causing a sustained up-estuary wind stress. Storm surge exceeded 2 m throughout most of the lower Chesapeake Bay. A 600 kHz acoustic Doppler current profiler (ADCP), deployed at a depth of 8.5 m off Gloucester Point, provided high-quality data on waves, storm surge, currents, and acoustic backscatter throughout the water column before, during, and after the storm. Pressure and salinity sensors at three additional sites further up the estuary provided information on water surface slope and saltwater excursion up the estuary. A first-order estimate of three terms of the along-channel momentum equation (barotropic pressure gradient, acceleration, and friction) showed that the pressure gradient appeared to be balanced by the wind stress and the acceleration during the storm. The storm’s path and slow speed were the primary causes of the extremely high storm surge relative to past storms in the area.
Christina L. Conrath
Several reproductive specializations are found within the elasmobranchs. All elasmobranchs fertilize internally and produce a relatively small number of large eggs. Elasmobranch fecundity generally ranges from one to two offspring produced a year up to a maximum of 300 in the whale shark (Compagno, 1990; Joung et al., 1996). Elasmobranch reproductive strategies include oviparity, aplacental viviparity and placental viviparity (Wourms, 1977). Oviparous species enclose eggs in an egg case and deposit them into the environment, where embryos develop external to the body of the mother . .Embryos remain in the egg case to develop for a period ranging from less than two months to over one year (Compagno, 1990). Viviparous species retain eggs within the uteri where the embryos develop. The yolk sac of placental viviparous species interdigitates with the uterine wall to form a placenta in which nutrients from the mother are transferred to the embryo. In most species the egg envelope is retained and incorporated into the uteroplacental complex (Hamlett, Wourms and Hudson, 1985). Gestation for viviparous species ranges from less than six months to greater than two years (Compagno, 1990). Viviparous species may have either lecithotrophic or matrotrophic development. Lecithotrophic development occurs when embryos derive their nutrition solely from yolk reserves and occurs in many aplacental viviparous species. Matrotrophic development occurs when embryos supplement the yolk reserves by obtaining maternally derived nutrients during gestation and also occurs in many aplacental species and all placental viviparous species (Wourms and Lombardi, 1992). The advantage of matrotrophy may be the increase in juvenile size at birth and therefore increased survivorship of young. Another important consideration in the evolution of elasmobranch reproductive strategies is the presence or absence of uterine compartments. Uterine compartments are formed in all species with placental development and some species with aplacental development and are believed to be an important step in the evolution of placental viviparity (Otake, 1990).
John A. Musick
Sharks and their relatives provide a multitude of usable products including: meat, fins, liver, skin, cartilage and jaws and teeth. Unfortunately, tens of millions of sharks taken in fisheries each year have their fins removed and their carcasses discarded overboard (Fowler and Musick, 2002). This practice, called finning, represents a considerable waste as the fins on average make up only about 5 % of the total weight of a shark (Vannuccini, 1999). Such waste is contrary to the United Nations Food and Agricultural Organization (FAO) Code of Conduct for Responsible Fisheries (Article 7.2.2 (g)) which stresses the importance of avoiding waste and discards in fisheries. In addition, the FAO International Plan of Action for the Conservation and Management of Sharks (IPOA- Sharks) encourages full use of dead sharks and retention of sharks from which fins have been removed (paragraph 22). Therefore, this Section briefly reviews the wide spectrum of uses that may be afforded by elasmobranchs to encourage their more complete and effective use. For a more comprehensive review see Vannuccini (1999) wherein an entire volume (470 pages) is devoted to the subject. A strong word of caution is necessary here: full utilization of shark carcasses should not be used as a pretext to fish unsustainably (Camhi, 2002). The goal of this manual is to provide information necessary to lead to sustainable elasmobranch fisheries.
Jian Shen, W. Gong, and Harry V. Wang
Hurricane Isabel made landfall near Drum Inlet, about 240 km south of the Chesapeake Bay mouth, on the Outer Banks of North Carolina at 17:00 UTC (GMT 12:00), 18 September 2003. Hurricane Isabel is considered one of the most significant tropical cyclones to affect portions of northeastern North Carolina and east-central Virginia. The ADvanced CIRCulation Model (ADCIRC) model was applied to the Chesapeake Bay to simulate Hurricane Isabel. High-resolution grids were placed inside the Bay and tributaries; coarse grids were placed outside the Bay. The spatial grid resolution in the Bay mainstem is about 200–1000 m and the spatial grid resolution in the tributaries ranges from 50–700 m. A parametric wind model was used to drive the model. The model results show that, with the use of a parametric wind model, the model can predict the peak surge and storm tide histories along the Bay mainstem and tributaries. The model was used to analyze the impact of sea level rise on surge and inundation prediction.
Robert J. Latour
Tagging methods have a long history of use as tools to study animal populations. Although the first attempts to mark an animal occurred sometime between 218 and 201 B.C. (a Roman officer tied a note describing plans for military action to the leg of a swallow and when the bird was released it returned to its nest, which was in close proxiD?ity to the military outpost in need of the information), it is uncertain when fish :"ere first marked (McFarlane, Wydoski and Prince, 1990). An early report published 1? The_ Comp/eat Angler in 1653 by Isaak Walton described how private individuals tied ribbons to the tails of juvenile Atlantic salmon (Salmo salar) and ultimately determined that Atlantic salmon returned from the sea to their natal river (Walton and (otton, ~ 898; McFarlane, Wydoski and Prince, 1990). Since the late 1800s, numerous fish tagging experiments have been conducted with an initial emphasis on salmonids followed soon after by successful attempts at tagging flatfish and cod. Pelagic species, namely Pacific herring (Clupea harengus pallasi) and bluefin tuna (Thrmnus thynnus) Were successfully tagged in the early 1900s, while elasmobranch tagging studies did not commence until the 1930s. Since 1945, large-scale tagging programmes have been initiated all over the world in an effort to study the biology and ecology of fish populations.
Modern tagging studies can be separated into two general categories. Tag-recovery studies are those in which individuals of the target population(s) are tagged, released, and subsequently killed upon recapture, as in a commercial fishery; while capture-recapture studies are designed to systematically tag, release and recapture individuals on multiple sampling occasions
H. Wang, J. Cho, J. Shen, and Y. P. Wang
An unstructured grid hydrodynamic model was used to study storm surge in the Chesapeake Bay during Hurricane Isabel. The model-simulated, storm-induced water level compared reasonably well with the measured data collected around the Bay. Calibrated water level was extracted from the model to further analyze the dynamics of the surge as it formed and propagated along the mainstem Chesapeake. Based on time-series analysis, formation of the surge due to the pumping of coastal waters (hereafter called the primary surge) into the Chesapeake was first identified at the Bay mouth with a peak height of 1.5 m above mean sea level (MSL). Once formed, it propagated northward with gradually diminishing amplitude at a speed of about 5 m⋅sec-1 until reaching Windmill Point, near the mouth of the Rappahannock River in Virginia. Beyond Windmill Point, the surge height increased monotonically toward the northern part of the Chesapeake Bay. Spatial analysis of surge height revealed that a second-stage surge was induced directly by the southerly wind following Hurricane Isabel’s passage inland. The persistent southerly wind induced a setup and a set-down in the upper and lower Chesapeake respectively, with the dividing line near Windmill Point where the water level stayed at approximately 0.5 m above MSL during the event. Space-time analysis provided further evidence that the abnormally high water in the upper Chesapeake Bay was the result of the primary surge wave as well as the second-stage surge caused by the southerly wind-induced setup.
A Global Perspective On The Effects Of Eutrophication And Hypoxia On Aquatic Biota And Water Quality
Robert J. Diaz, Janet Nestlerode, and Minnie L. Diaz
Development associated with human populations has led to the globalization of many environmental problems. In marine systems, the most serious of these problems are directly related to the process of eutrophication. The increased production of organic matter in these marine systems associated with eutrophication is the primary factor impacting species abundance and composition and dissolved oxygen budgets. Oxygen, which is essential to maintaining balance in ecosystem processes through its role in mediating microbial and metazoan activities, has declined to critically low levels in many systems, which has led to the development of hypoxia (<2 ml O2>/l) and anoxia (0 ml O2/l). Currently, most oxygen depletion events are seasonal, but trends toward longer periods that could eventually lead to persistent hypoxic or anoxic conditions are emerging. Over the last 50 years, there has been an increase in the number of systems reporting problems associated with low dissolved oxygen. Currently there are over 100 hypoxic/anoxic areas around the globe, ranging in size from <1 km2 to 70000>km2, that exhibit a graded series of responses to oxygen depletion, ranging from no obvious change to mass mortality of bottom fauna. Ecosystems currently severely stressed by eutrophication induced hypoxia continue to be threatened with the loss of fisheries, loss of biodiversity, alteration of food webs, and simplification of energy flows.
Michael C. Newman
Fish are suddenly exposed to hypoxic conditions during diverse events such as seiche- or turnover-related water movements, bottom water release from reservoirs, ice-over of eutrophic arctic lakes, and rapid shifts in respiration: photosynthesis associated with cultural eutrophication. In each case, chemical equilibria established under hypoxic conditions that result in metal dissolution and accumulation suddenly shift toward chemical equilibria of oxic conditions. Critical changes in speciation include those determining the free ion activity that, as expressed by the Free Ion Activity Model (FIAM), is often the most bioactive form of a dissolved metal. Metal phase can also change rapidly and, in some cases, result in a precipitate on respiratory surfaces. Exposure of fish gills to metal (and integument of larval or small fish) changes O2 exchange dynamics. Changes in mucus quality and production and lamellae morphology decrease the amount of effective gill exchange surface and increase the diffusive layer thickness. These changes exacerbate those associated with the reduced O2 partial pressure gradient. Consequent shifts in blood chemistry (e.g., pH and ion composition) and ventilation also affect metal transport and deposition within fish tissues. Some of these changes have immediate consequences, but others can continue for long periods after the hypoxic conditions pass. Long-term metal effects can influence fish tolerance during future hypoxic episodes.
A joint, similar action model can be applied if the parsimonious assumption is made that asphyxiation constitutes a common mode-of-action for both acute metal effects and hypoxia. Joint action models are applicable based on either conventional dose-effect or survival time approaches. Expansion of such models to a physiologically-based toxicokineticstoxicodynamics framework (e.g., framed around the Fick equation) would be desirable, provided that model parameter requirements remain realistic. Long-term effects may be better addressed with models such as the binary logistic models used by epidemiologists.
John A. Musick and Julia K. Ellis
The factors that may either constrain or contribute to sustainable marine fisheries were examined by reviewing and analyzing the history and current status of several U.S. fisheries. Among major factors under consideration are inherent vulnerability (vulnerability in some species is high because of low intrinsic rates of increase and/or naturally infrequent recruitment); environmental degradation (fisheries may collapse because of anthropogenic habitat destruction); availability of data (information necessary co conduce accurate stock assessments may be inadequate for some species); quality of the scientific advice (inappropriate models or scientifically inaccurate assessments may be used); and effectiveness of management decisions (managers may disregard recommendations from scientific committees, and/or implement management measures chat are risk-prone). Fisheries that are examined include the Atlantic Coast striped bass Morone saxatilis fishery, the New England groundfish fishery, the Atlantic shark fishery, the Atlantic and Gulf reef fish fisheries, and the Pacific rockfish fishery. Although many of the factors listed above contributed co declines in these fisheries, the root cause in all cases was harvesting at rates that were much higher than could be sustained by recruitment. Management was largely ineffective because management decisions were risk-prone and motivated by short-term economic considerations rather than long-term sustainability. Only after passage of legislation not only authorizing but specifying mandatory stock rebuilding, has most management been sufficiently precautionary to allow sustainability.
James E. Kirkley, Rolf Fare, Shawna Grosskopf, Kenneth McConnell, Dale E. Squires, and Ivar Strand
Excess capacity is globally recognized by resource managers as a major problem for fisheries. Yet, the concept of capacity remains vague, ill-defined, and often ambiguous. Presently, measuring capacity and capacity utilization in fisheries has become more important or of greater public concern than ever because of various national and international agreements or policies to reduce capacity in fisheries throughout the world. In this study, we propose data envelopment analysis (DEA) as one method that may be used to calculate a production-oriented measure of capacity. We conclude that although the DEA approach is limited and does not provide measures of capacity and CU consistent with the long-run optimum scale of operation, it can provide information useful to resource managers concerned with downsizing fleets or matching capacity to resource levels. We illustrate the approach by examining the capacity of ten sea scallop vessels operating between 1987 and 1990. We conclude that the ten vessels had the capability to harvest considerably more than they actually did, and the fleet should be reduced by 68 percent or more if managers desire to match capacity to a recommended sustainable yield of 20 million pounds
James E. Kirkley and Dale Squires
The definition and measurement of capacity in fishing and other natural resource industries possess unique problems because of the stock-flow production technology, in which inputs are applied to the natural resource stock to produce a flow of output. In addition, there are often multiple resource stocks, corresponding to different species, with a mobile stock of capital that can exploit one or more of these stocks. In turn, this leads to three unique issues: (1) multiple stocks of capital and the resource; (2) that of aggregation or how to define the industry and resource stocks to consider; and (3), that of latent capacity or how to include stocks of capital that are currently inactive or exploit the resource stock only at low levels of variable input utilization. This paper presents appropriate definitions of capacity and methods for measuring capacity in fishing industries taking into consideration these issues.
James E. Kirkley, Dale Squires, Mohammad Ferdous Alam, and Ishak Haji Omar
Many developing countries pursue offshore fisheries development strategies to increase protein supply, expand employment, earn foreign exchange, and militate the conflict between large- and small-scale fisheries over the inshore resource stocks. This study evaluates the economic success of Peninsular Malaysia's offshore fisheries development policy for the west coast purse seine fleet, finding it has largely succeeded on economic grounds
Neils Vestergaard, Dale Squires, and James E. Kirkley
Different measures of capacity utilization (CU) are applied to the Danish Gillnet fleet using the Data Envelopment Analysis (DEA) approach. The potential capacity output is found using the output-orientated measure. The CU measures are the partial capacity utilization measure and the Ray measure (DEA measure). The average CU of the Danish Gillnet fleet was found to be between 0.85 and 0.95 depending on the measure used. Since the Danish Gillnet fleet participates in a multispecies fishery regulated by TACs (output) the excess capacity was also found for each species. The results show higher excess capacity for cod and sole than for other species, which is in accordance with how the fishery developed. The variable input utilization was also estimated. On average, the variable input could have been increased by 27 percent in the period examined. Finally, the results are interpreted with respect to fishing area, port, vessel size and catch composition.
Dale Squires, Yongil Jeon, R. Quentin Grafton, and James E. Kirkley
In fisheries, overcapacity is a critical problem that reduces rents and jeopardizes the sustainability of stocks. Using data from the British Columbia (BC) halibut fishery, before and after tradeable property rights were adopted in the harvesting sector, the paper tests for the effects of private rights on capacity and capacity utilization. The results indicate that tradeable property rights can be effective, even in the short-term, at reducing capacity per vessel per day and provide incentives to help overcome the "Tragedy of the Commons".
Rochelle D. Seitz, Romauld N. Lipcius, William T. Stockhausen, and Marcel M. Montane
Sanctuaries can potentially protect a significant fraction of the spawning stock, and thereby sustain heavily exploited populations. Despite the worldwide use of marine and estuarine spawning sanctuaries, the effectiveness of such sanctuaries remains untested. We therefore attempted to quantify the effectiveness of the spawning sanctuaries for adult female blue crabs (Callinectes sapidus) in Chesapeake Bay. We used baywide winter dredge survey data to estimate the potential spawning stock prior to the major exploitation period, and summer trawl survey data to estimate spawning stock abundance within the Lower Bay Spawning Sanctuary and adjacent Bayside Eastern Shore Sanctuary during the reproductive period. Hence, we were able to approximate the percentage of the potential spawning stock that was protected by both sanctuaries after exploitation. On average, approximately 16% of the potential spawning stock survived to reach the Lower Bay Spawning Sanctuary and Bayside Eastern Shore Sanctuary. Even under a best-case scenario (i.e., crab residence time of 2 weeks), the sanctuaries only protected an estimated 22% of the potential spawning stock, which is well below the percentage recommended by recent stock assessments for sustainable exploitation (28%). In the worst case, a mere 11% of the potential spawning stock survived to reach the spawning sanctuaries. Hence, we recommend a substantial expansion of the spawning sanctuaries, as well as the complementary protection of other life stages in critical habitats, such as nursery grounds and dispersal corridors. Furthermore, traditional fisheries management measures (e.g., effort control) should be used in concert with sanctuaries to thwart impediments to effective implementation of the sanctuaries, such as redirected fishing effort.
William J. Hargis Jr. and Dexter S. Haven
The eastern oyster, Crassostrea virginica (Gmelin), can live any place in coastal marine and estuarine waters of the North American east coast offering suitable setting and survival opportunities. It occurs singly or in small clumps scattered widely but thrives best in colonial aggregations which, like those of tropical corals, are truly reefs. The massive self-renewing oyster reefs ("whole banks and beds") reported by early Chesapeake observers have yielded much. Without readily accessible oyster reefs the first English colonists of Jamestown might have starved. Without them the rich oyster industries of later years could never have developed.But oyster reefs benefitted the oysters that built and maintained them as well as the humans using them.
The oyster reefs of the Chesapeake region, including those on Seaside, developed during some 7,000-6,000 years of Bay evolution during the current (Holocene) Epoch. Until about 200 years ago reef oyster populations were able to maintain themselves and their reef habitats and withstand the inroads of biological enemies, other natural hazards and increasing harvests. By the late 1800s, Chesapeake public market oyster harvests had peaked and total market harvests and the oyster populations which provided them were in decline. more ...
Materials Processing by Oysters in Patches: Interactive Roles of Current Speed and Seston Composition
Deborah A. Harsh and Mark W. Luckenbach
Filtration rates for oysters have typically been measure in still water laboratory experiments and ecosystem-level effects estimated by extrapolation. With the exception of in situ measures of oyster filtration by Dame (1999, Chapter 18, this volume and references cited therein) these estimates have failed to account for the effects of hydrodynamic effects on oyster filtration rates and on physical redistribution of particles. In this chapter we report on a series of experiments conducted in a recirculating seawater flume designed to address the effects of flow speed and seston composition on filtration rates in a bed of oysters. In six separate experiments ninety oysters were arranged in the bed of the flume, flow speed adjusted to one of eight levels (0.65, 1.0, 2.1, 4.2, 6.0, 10.4, 13.7 or 22.0 cm s·1 ), seston added to the flume and particle concentrations upstream and downstream of the oyster bed determined from vertically-arrayed samples. Four experiments investigated the effects of each flow speed on the filtration of a unialgal diet, while two experiments utilized the algal diet in combination with inorganic particles. Control experiments sought to estimate the effects hydrodynamic effects on particle distribution by measuring "filtration" rates over beds of ninety pairs of empty oyster valves. Our findings reveal effects of flow speed and, less evidently, seston composition on particle filtration by oysters. More importantly, our results point to the importance of hydrodynamically-mediated particle redistribution of particles over patches of oysters, and portend sampling difficulties associated with quantifying oyster filtration rates in the field.
James Wesson, Roger Mann, and Mark Luckenbach
Long-term restoration of the Virginia Oyster resource has been assisted by a series of governmental and regulatory initiatives. Following the 1990 Blue Ribbon Panel the Virginia Marine Resources Commission set as goals that the oyster resources and oyster fishery would be so managed as to achieve (a) no net loss of existing standing stock of the native oyster over the next five years, and (b) a doubling of the existing standing stock of the native oyster over the next ten years. The 1994 Chesapeake Bay Aquatic Reef Plan and Oyster Fishery Management Plan both recommended the creation of 5,000 acres (2024 hectares) of oyster reef habitat during the 1995-2000 period. Practical progress toward this goal has been made through the development of several programs including direct application of substrate (cultch) to extant oyster reefs to facilitate settlement and recruitment, enhancement of reefs of the Seaside of the Eastern Shore by exhumation of buried shell, and construction of elevated reef structures in the Virginia subestuaries of the Chesapeake Bay. Efforts in the James River have included subtidal berm type structures capped with shell and a reef constructed entirely of shell. A shell reef has been constructed in the Piankatank River, and construction of several more is planned. All reefs remain as brood stock sanctuaries. Continuing management is supported by quantitative stock assessment.
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