A bioeconomic simulation model of the middle Atlantic surf clam (Spisula solidissima) fishery has been developed from a survey of biological and econometric relationships. While identifying the biological input parameters available in the literature, the economic submodel of the fishery has been developed with price and landings time series data, and with data obtained through the use of survey questionnaires and interviews with surf clam fishermen and processors. Alternative management scenarios in the fishery have been evaluated from industry costs in both the harvesting and processing sectors and analysis of the demand for raw product confronting surf clam fishermen. Multiple regression analysis of time series data indicates that surf clam ex-vessel prices may be negatively related to surf clam landings whereas hard clam prices are positively related to ex-vessel ocean quahog prices and ex-vessel oyster prices. The strength of this relationship confirms the status of ocean quahogs as very close substitutes for surf clams. The results of case studies using the model suggest that the Mid-Atlantic Fishery Management Council has followed a prudent course of action in managing the surf clam fishery. The model also projects that, (1) larger yield quotas may be possible in the immediate future without jeopardizing surf clam population stability, (2) overcapitalization in the fishery appears to remain a problem, and (3) the economic outlook for the operators of small vessels remains relatively bleak.

The logistical difficulties of research in extremely low temperatures and lack of access to the Arctic have meant that there is a historic dearth of knowledge of coastal Arctic biogeochemistry, especially during winter when sea ice is present. Recent observations, however, indicate that the Arctic is changing rapidly. Changes include increased temperatures, decreased extent and volume of sea ice, and increased freshwater inputs. How these changes influence biogeochemical cycles is an open question, especially in the highly productive coastal regions of the Chukchi Sea. Here I present nitrogen (N) uptake and regeneration rates for phytoplankton and bacteria measured in the shallow waters and landfast sea ice near Barrow, Alaska. Experiments were performed using tracer-level incubations of stable isotope (15N) ammonium, nitrate, urea, and amino acids during January, April, and August over two successive years (2010 --- 2012). Autotrophic versus heterotrophic N uptake was measured with traditional size fractionation. In brief, I found that outside of the spring phytoplankton bloom period, ammonium and amino acids were the preferred N substrates assimilated. Regeneration of N and nitrification were especially high during winter. A high-speed cell sorting flow cytometer was used to distinguish bacterial sub-populations and their uptake rates. Low nucleic acid populations were active in taking up N compounds, although not at quite the same rate as high nucleic acid cells. The difference was less pronounced during winter compared to summer. Additional experiments were designed to artificially warm the samples to demonstrate that ammonium uptake rates increased with temperature and substrate availability, whereas nitrification rates did not. Uptake and regeneration of ammonium and nitrate along with nitrification was also measured in landfast sea ice. This is the first report of N uptake from within the sea ice matrix in the Chukchi Sea. Given the paucity of information on N cycling in the Arctic Ocean, these data can inform modeling efforts to predict future changes in the system and also provide a baseline by which to compare future observations.

The spot (Leiostomus xanthurus) is an important commercial and recreational species in Virginia. Recruitment of juveniles to the Bay is characterized by large interannual fluctuations, that can be explained by the sequence and direction of wind during various phases of the early life history. An environmentally-modified Ricker stock-recruitment curve was developed incorporating the southeasterly winds in November-December, the southerly winds in January-March, and the westerly winds in April-May. This model explained 81% of the variation and closely paralleled the VIMS Juvenile Spot Index. Spot from the Chesapeake Bay migrate south in fall to spawn near or south of Cape Hatteras. Larvae were distributed over the shelf south of Oregon Inlet in February and early March, with the youngest larvae found over the outer shelf off Cape Hatteras. By late March, spot were distributed over the inner shelf north of Oregon Inlet to the mouth of the Chesapeake Bay. Age and size of larvae increased in a northward and shoreward direction. The persistence of larvae over the inner shelf north of Oregon Inlet suggests that a mechanism for northward transport occurs in this area. Northward transport over the inner shelf in the southern MAB is possible with multiple southerly wind events. Spot larvae would not have to be transported the entire distance to the Chesapeake Bay entrance, but only to where the bottom layers of the water column are moving toward the Bay. Recruitment to the Chesapeake Bay began in February or March of 1990 and in April of 1989 and lasted for two months. Spot entering the Bay were approximately 84 days old and 14.0 mm SL. The birthdates of spot collected offshore in the southern MAB and those at the Bay mouth were very similar, suggesting that recruits to the Bay were from the same pool of larvae collected earlier in the season and providing further support for a spawning location south of Cape Hatteras and not off the Chesapeake Bay as previously reported.

Nearly half of the known species of sharks in the world live in the deep sea, yet little is known of the biology or life history of these important predators of the deep. Fishing effort for deep-water sharks, both targeted and incidental, has been increasing worldwide over the last few decades. However, in most cases the impact of this harvest is unknown due to the paucity in landings data and the lack of stock assessments for these species. This research was conducted to provide some of the basic life history information needed to improve the understanding and properly manage deep-water sharks. Specifically, information is presented herein on age determination using dorsal fin spines; the potential for radiometric age validation using dorsal fin spines; the age, growth, and reproductive biology of Squalus mitsukurii from Hawaiian waters; and the reproductive biology and embryonic development of Centrophorus cf. niaukang and Etmopterus princeps.;Dorsal fin spines offer an alternate structure for age determination in phalacanthous chondrichthyans. In this study, I sought to identify optimal methods of age determination using dorsal fin spines of 14 species of squaliform sharks and two species of holocephalans. Growth bands can be found in three zones of the fin spine: on the enamel cap (if present), at the base of the whole spine, or in the inner dentine layer. Each of these three methods was applied to fin spines from these 16 species. Results of each method are compared and discussed, with an optimal aging method suggested for each species.;Radiometric methods have been used to validate age estimates from teleost otoliths, shark vertebrae, and coral skeletons. The radioisotopes 210Pb and 226Ra were ineffective for age determination of dorsal fin spines, possibly due to a violation of the assumption of constant isotopic uptake, or conversely the spine may not act as a closed system.;A study of age, growth and reproductive biology of Squalus mitsukurii was conducted near Oahu, Hawaii. Age estimates ranged from 3 to 26 years for females and 6 to 23 years for males. Growth parameters estimated with multiple growth models indicated that this a K-selected species, characterized by high longevity, late maturity, and slow growth. Observed fecundity also indicated that reproductive output is low for this species.;A study of embryonic development in Centrophorus cf. niaukang and Etmopterus princeps indicated that the process of embryogenesis results in a range in organic matter depletion from the time of fertilization to parturition. Centrophorus cf. niaukang embryos showed a reduction of 19.5% in organic matter, while E. princeps embryos showed a reduction of 7.8% in organic matter over the course of embryonic development. These results indicate that at least one of these species may be matrotrophic. Observed fecundity and maturity ogives are also presented for each species.;This study on age determination, growth, and reproductive biology of several species of deep-water sharks and holocephalans indicated that these are K-selected species. Future harvest of these species should proceed with caution, as they are prone to overexploitation and localized depletion.

The objective of this study was to identify important river and estuary habitats of young American shad by estimating their value to fish production. American shad populations across the Atlantic coast have been in decline since the 1800s due, in part, to restricted access to habitat and habitat loss. The study demonstrates that production and year-class strength of Mattaponi River American shad are influenced by allochthonous subsidies from riparian and terrestrial ecosystems, thus habitat quality is related to the watershed's health, and that Chesapeake Bay is an important overwintering habitat for juveniles. Specifically, I characterized production dynamics and biogeochemical processes in the Mattaponi River, a tributary of the York River and the most productive American shad nursery in Virginia's portion of Chesapeake Bay; quantified the contribution of autochthonous and allochthonous organic matter (OM) to zooplankton, macroinvertebrates, and young American shad in the Mattaponi River; identified the trophic pathways that support American shad production within river and estuary habitats during ontogeny; and determined the main habitats within the York River system, from the larval stage to their ocean migration. Mattaponi River production dynamics were strongly influenced by river discharge; during periods of high discharge, primary production was suppressed and greater than 60% of zooplankton, macroinvertebrates and larval American shad production was supported by allochthonous OM. Further, OM concentration, plankton density, and juvenile American shad indices were elevated, demonstrating that allochthonous OM subsidizes the metazoan food web and fish production. Spatial segregation of juveniles rearing in the freshwater nursery zone was identified through a novel application of a stable isotope turnover model; juveniles were shown to reside in habitats of 5-10 river km for a month or longer. These fish emigrate from the nursery zone in November and December, residing and feeding in the York River estuary and Chesapeake Bay before migrating to the ocean in February through April. Variable emigration strategies were observed; most American shad likely emigrated at 2-5 g and spent weeks to months in the estuary, however a few emigrated at habitat.

The value of habitats in terms of biological production is of interest to ecologists and resource managers. Seagrasses are a commonly occurring habitat type in shallow marine waters and have been shown to support high abundances of fish and invertebrates. In lower Chesapeake Bay, seagrasses grow in a shallow fringe in the subtidal zone. Although, ample evidence exists for the value of these habitats as foraging and rearing areas for a variety of organisms, the connectivity among species and the benefits derived from these habitats in terms of production have not been well described, especially for small, seasonally occurring finfishes. The main objective of this research was to document fish occurrence and abundance, describe trophic interactions within the seagrass community, and quantify export of biomass from the habitat using a model species to demonstrate the value of these habitats in terms of finfish production.;To address the research objective, I employed a variety of models---statistical, ecosystem, and individual-based. In Chapter 1, I conducted as census of finfishes in seagrass habitats and compared contemporary occurrences and abundances to data from the 1970s. This chapter showed that the fish fauna in these habitats is dominated by a small number of abundant and commonly occurring species, including Spot (Leiostomus xanthurus), Silver Perch ( Bairdiella chrysoura), Bay Anchovy (Anchoa mitchilli), Atlantic Silverside (Menidia menidia), Dusky Pipefish ( Syngnathus floridae), and Northern Pipefish (Syngnathus fuscus ). While abundances had changed since the 1970s for some species, most were highly variable with no discernible trend. There was a small decrease in species richness from the historical dataset to the contemporary dataset and multivariate analysis showed a shift in community composition. The data from this chapter formed the basis for the ecosystem model developed in Chapter 2. In this model, biomass, production, and diet data were inputs, and using a mass-balance approach, a food web model was iteratively developed. There were 35 model compartments in the model and scenarios based upon historical data and future projections were developed for comparison. Mesozooplankton were the most highly connected group, while piscivorous birds, several piscivorous fishes, and mesograzers were all considered keystone groups, controlling food web dynamics. In Chapter 3, an individual-based model was developed for Silver Perch, to assess growth and production within a seagrass habitat. Because Silver Perch settle in this habitat, grow during the summer season, and migrate to deeper waters in the fall, they were an appropriate model species for determining the contribution of seagrass habitats to production. With high seasonal abundance and rapid growth (~0.19 g/d), this species contributes a considerable amount of biomass to Chesapeake Bay, biomass that originates in seagrass habitats and moved via trophic transfer.;This study presents a quantitative view of community ecology in lower Chesapeake Bay seagrass habitats. With changing temperatures and habitat loss, these habitats are at risk, and this study demonstrates that their value to the Chesapeake Bay food web extends beyond the small fringe of their occurrence.

No description available.

No description available.

No description available.

Delineation of essential fish habitat is particularly difficult for migratory fish which utilize large expanses of habitat throughout their life history. This study's main objective was the development and evaluation of habitat assessment tools for the early life stages of American shad (Alosa sapidissima) in two coastal plain rivers. to accomplish this, shad spawning and larval nursery habitats were delineated in the Mattaponi and Pamunkey rivers using presence of eggs and larvae (1997--1999) as evidence of habitat use. A watershed habitat assessment protocol was developed and used to rate habitat based on hydrographic, physical habitat, shoreline and land use parameters. These parameters were evaluated for associations with the presence of shad eggs and larvae to corroborate habitat ratings. Values for parameters used in the ratings were obtained from field assessments, long-term data sets and remote sensing in attempts to combine best-available data. Multivariate statistical analyses indicate the importance of hydrographic parameters (current velocity, dissolved oxygen and depth); physical habitat features (sediment type and deadfall); and forested shoreline/land use features to presence of eggs. Larvae were more dispersed than eggs and distinct habitat associations could not be discerned. Morphological features indicate the presence of three distinct regions along the Mattaponi and Pamunkey river gradients. Presence of eggs is typically associated with upstream and mid-river regions, while larvae were dispersed amongst the three regions. Shad eggs and larvae were more abundant on the Mattaponi River than the Pamunkey River, which is concordant with juvenile abundance. Abiotic factors hypothesized to impact spawning location, larval transport, development rates and predator/prey abundance were also examined. Utilizing the juvenile Alosa index (1991--1999) as an estimate of juvenile shad recruitment, correlation with discharge, precipitation and water temperature (March--June) was examined. Hydrographic conditions during May and June appear to most accurately predict juvenile recruitment patterns in the Mattaponi River, however trends in the Pamunkey River were not as consistent. Ultimately, discharge affects transport of weak-swimming larva to variably favorable nursery habitats. A conceptual hydrodynamic model was developed which explores potential impacts of variable habitat exposures on larvae driven by spawning location, habitat suitability, discharge and hatching rates.