No description available.

The effect of triploidy to effect faster growth and increased survival compared to diploid oysters is called the ‘triploid advantage’ and this advantage in the Chesapeake Bay for Crassostrea virginica is the principal reason for the value of triploid C. virginica in the Chesapeake Bay, USA. The triploid advantage is hypothesized to be the result of genetic effects, physiological changes, or a combination of both. The causative genetic mechanisms at play may include additive genetic effects and heterosis while the physiological changes obtain from triploid sterility. The triploid advantage was examined by comparing 13 diploid and 13 triploid crosses across three environments. The genotypes used in this study consisted of wild stocks from both the Virginia and Maryland portions of the Chesapeake Bay, four lines from ABC’s 2006-year class of selected lines, and four ABC Superlines. Three experimental sites, ranging in salinity and disease pressure (Choptank River – low salinity and no disease pressure; Rappahannock River – moderate salinity and occasional disease pressure; York River – higher salinity and consistent disease pressure) were chosen to investigate the influence of environment on triploid advantage. Growth metrics (shell height, whole wet weight, and wet tissue weight) and survival rates among diploid and triploid C. virginica were recorded. The triploid advantage for growth and survival ranges from positive to negative depending on environmental factors. In the low salinity environment, triploidy proved disadvantageous regardless of the genotype of the diploid parent. As salinity increased so did the triploid advantage, which was greater for the more disadvantaged (wild) groups. In the Rappahannock River, with moderate salinity and no disease pressure, selected diploids performed equivalently to their triploid counterparts showing that breeding efforts can improve diploid field performance to rival triploids. In the York River, under disease pressure, triploids offered the greatest advantage. Triploids from both wild-type and selected diploids had higher growth and survival than their diploid counterparts under disease pressure. In addition to greater survival, triploids also had lower Dermo infection prevalence than diploids indicating that there is a triploid advantage for Dermo disease resistance, perhaps as a result of triploid sterility. Variation in the effect of triploidy on field performance follows the notion that triploidy may be thought of as a tool useful in some applications but not in others. For low salinity, it appears that triploidy may not be the appropriate tool for providing benefits for oysters but for oysters grown under disease pressure, it certainly is. The triploid advantage appears to be caused by both genetic effects and physiological changes, with the environment influencing the expression of each in manifesting the triploid advantage.

White Marlin (Kajikia albida) is a highly migratory species that occurs throughout temperate and tropical regions of the Atlantic Ocean and is the basis of a large sport fishery along the United States Atlantic coast. The single, Atlantic-wide stock is considered to be overfished, with less than one-third the spawning biomass estimated to be necessary for maximum sustainable yield. Billfish management measures adopted by the International Commission for the Conservation of Atlantic Tunas (ICCAT) and implemented in the U.S. by the National Marine Fisheries Service (NMFS), as well as increasing angler awareness of conservation, have resulted in the vast majority of White Marlin being released after capture. In 2003 it was estimated that more than 99% of the 4,000-8,000 White Marlin captured each year in the U.S. recreational fishery are released alive. Recent research aimed at estimating the rate of post-release mortality suggests that it may vary with hook type, hook location, angling time, air exposure, relative temperature change, and the size of the fish. Stress resulting from an angling event may also have sublethal physiological effects that negatively impact growth rates, reproductive output or investments, ability to evade predators, and disease resistance. I examined post-release mortality and post-angling physiological stress by collecting physiological data from blood samples and deploying pop-up satellite archival tags (PSATs) on recreationally angled White Marlin. Over two field seasons blood samples were collected from 68 recreationally caught White Marlin of which 22 were tagged with PSATs distributed over three stratified angling-time categories: short (0-10 min, n=8), medium (10-20 min, n=7), and long (>20 min, n=7). Plasma glucose, sodium, and cortisol increased significantly with fight time, plasma potassium decreased significantly with fight time, and plasma lactate and chloride increased significantly with fight time and water temperature. Habitat utilization following release was not affected by physiological status, angling time, lower jaw fork length (LJFL), or sea surface temperature. These results demonstrate that increased angling times and warmer water result in greater physiological stress in White Marlin. A 21% post-release mortality rate was inferred from PSAT data, and if non-reporting and early releasing tags are additionally assumed to be mortalities, post-release mortality could be as high as 32%. Post-release mortality was not related to fight time, LJFL, or sea surface temperature and was marked by elevated plasma potassium concentrations regardless of which mortality scenario was assumed. My estimates of post-release mortality rates in this study were more than an order of magnitude higher than had been previously assessed for White Marlin caught on circle hooks. This disparity in estimates may indicate that either blood sampling, removing fish from the water, or some combination of the two greatly increased post-release mortality. In order to maintain low rates of post-release mortality anglers should not remove White Marlin from the water and should resuscitate fish regardless of angling time.

The Striped Bass (Morone saxatilis) is an anadromous finfish that supports a lucrative fishery along the Atlantic coast of the United States and serves as a vital component of estuarine food webs. Once Striped Bass stocks were restored after crashing in the late 1980s, abundance skyrocketed to record levels. Over the past decade however, abundance has steadily declined, concurrent with an outbreak of mycobacteriosis. Disease prevalence is currently >50%, and previous research has demonstrated diseasepositive fish exhibit slower growth and increased natural mortality compared to diseasenegative fish. The purpose of this research was to provide a contemporary description of Chesapeake Bay Striped Bass reproductive metrics, which have not been thoroughly described since the stock crashed but before it rebounded. Additionally, the effects of mycobacteriosis on reproductive output were assessed via egg-per-recruit analysis. Female Striped Bass were collected from the York, James, and Rappahannock Rivers and the mainstem of the Chesapeake Bay from 2003-2013. Oocyte development, maturity, oocyte size, fecundity, the gonadosomatic index, and oocyte dry mass were fit to regression models against age, length, or weight in order to determine the influence of month, year, disease prevalence, and female pre-spawning condition. The best fitting models for maturity-at-age and fecundity-at-length were combined with a growth model and estimates of fishing mortality and disease progression to create egg-per-recruit models that simulated the effects of decreased growth and increased natural mortality due to disease on the lifetime reproductive output of Chesapeake Bay Striped Bass. Lower age-at-maturity was seen for disease-positive fish compared to disease-negative fish, but no other reproductive metrics were affected. The increased natural mortality caused by the disease was shown to appreciably reduce reproductive output. This study provides critical biological metrics that can be used to inform future studies and reveals the extent to which mycobacteriosis can influence Striped Bass population dynamics.

No description available.

The Chesapeake Bay and coastal waters of Virginia, U.S.A. serve as foraging grounds for loggerhead (Caretta caretta) and Kemp’s ridley (Lepidochelys kempi) sea turtles from approximately May to October each year. Both loggerheads and Kemp’s ridleys are known to feed primarily on benthic invertebrates as juveniles and adults, but specific prey preferences vary between geographic regions. The Virginia Institute of Marine Science Sea Turtle Program has collected diet data and gut samples from stranded and incidentally caught sea turtles in Virginia since 1979. Examination of turtles that stranded in Virginia during the late 1970s and early 1980s indicated that loggerheads fed primarily on Atlantic horseshoe crab (Limulus polyphemus) and Kemp’s ridleys primarily on blue crab (Callinectes sapidus). During 1980 to 1994, 1997, and 2000 to 2002, 128 whole digestive tract samples and 41 partial gut samples were collected from loggerheads in Virginia. Diet information was noted on stranding datasheets for an additional 134 loggerheads from 1980 to 2002. Twenty-three whole samples and 10 partial samples were collected in Virginia from Kemp’s ridleys during 1987 to 1994 and 2000 to 2002, and data were available on an additional 26 ridleys from 1983 to 2002. Prey items in the samples were identified to the lowest possible taxonomic level, and dry weights and prey item counts were recorded. Results indicate a shift in loggerhead diet from predominantly horseshoe crab during the early to mid-1980s to predominantly blue crab during the late 1980s and early 1990s. Loggerhead diet in the mid-1990s and 2000 to 2002 was dominated by finfish, particularly menhaden (Brevoortia tyrannus) and croaker (Micropogonias undulatus). These diet shifts suggest that fishery-related declines in horseshoe crab and blue crab populations have caused loggerheads to instead forage on fish caught in nets or on discarded bycatch. A slight seasonal effect on diet was also detected, and the diet of juvenile loggerheads differed somewhat from that of the adults. The small Kemp’s ridley dataset suggests that blue crabs and spider crabs (Libinia spp.) were important components of ridley diet in Virginia during 1987 to 2002.

Wetland mitigation has become a 2.4 billion dollar per year industry in the U.S. and in Virginia it leads to the replacement of 77 ha of palustrine forested wetlands (PFWs) per year with mitigation wetlands, including created forested wetlands (CFWs). Mitigation hinges on the idea that compensation wetlands lead to “no net loss of wetland function” when compared to impacted wetlands. We assessed the functions of provision of habitat and biogeochemical functions associated with production of biomass, the retention and removal of nutrients and the accumulation of soil C over 8 years in seven CFWs of approximately 11 and 20 years and compared them to natural reference wetlands (NRWs). CFW plant communities were similar to NRWs in all measured parameters in the herbaceous and shrub/sapling strata and in all strata combined. However, non-native dominance showed a significant positive linear relationship with CFW age. In the tree strata, 11 year old (yo) CFWs had lower richness than NRWs and both age classes of CFWs had lower FQI than NRWs. NRWs held 10 to 20 times more carbon in woody biomass than CFWs. Tree species composition was significantly different between CFWs and NRWs, however NRW trees were similar to CFW saplings. 11 yo CFWs held lower percentages of C, N and P and had higher Db than NRWs in both the 0-10 and 10-20 cm depth. 20 yo CFWs developed similar levels of %C, %P, bulk density (Db), and nutrient ratios in the surface and displayed rapid increases in %C and %N over 8 years. However, CFWs offered 45% lower soil total soil C storage and 50% lower %N. Furthermore, all CFWs stored lower nutrient levels than NRWs in the 10-20 cm soil depth. We found that FQI correlated positively with total C accumulation rates in woody biomass and soil C, indicating that biogeochemical function and the provision of habitat can be complimentary in CFWs. Finally, 11 and 20 yo CFWs adhered to the regulatory performance standards established for Virginia in terms of stems per ha and wetland indicator status, but all wetlands (including NRWs) failed to achieve <5% non-native species cover.

No description available.

The blue crab Callinectes sapidus supports one of the most important fisheries in the Chesapeake Bay and is the leading contributor to blue crab landings in the United States. Assessment and management of blue crab stocks has been hampered by a lack of estimates of natural mortality rates, a key parameter in assessment models. In Chapter 2, we demonstrate that the approach used for estimating natural mortality that had been used in past assessments was flawed, and provide justification for a superior alternative. In Chapter 3, we synthesize our current understanding of natural mortality rates in adult blue crab and provide a suite of estimates for the Chesapeake Bay stock. Our estimates were used in the 2005 assessment for this stock, and the methods and estimates can provide guidance for assessments of the same or other species. In addition to estimates of natural mortality for adult blue crab, the short turnover time in the stock makes it necessary to consider changes in natural mortality rates with size or age. Current assessment models use an annual time step, which smooths over the changes in natural mortality that occur during ontogeny. Some crabs reach an exploitable size within the first year of life, and smaller crabs are expected to have higher natural mortality rates. In addition, natural mortality is known to vary seasonally, being highest in Chesapeake Bay during the summer months when predators are most abundant and crabs are molting frequently. to include size-dependent mortality in more realistic population dynamics models, we estimated mortality rates of juvenile crabs through field experiments (Chapter 4). In 2005 and 2006, we estimated mortality rates of seven cohorts of hatchery-reared juveniles in two tidal marsh creeks along the York River, Virginia during the summer and fall. Juvenile mortality rates were orders of magnitude higher than current estimates of adult mortality rates and were highest in the summer. Our results reinforce concerns about the adequacy of current assessment models and provide estimates of mortality that can be used to guide future work.

No description available.