The results of life history studies involving the sailfish, Istiophorus platypterus, from the Atlantic, Pacific, and Indian oceans were reviewed. Results of studies agree on several aspects of sailfish biology; sailfish exhibit opportunistic feeding behavior, follow the 28??C isotherm, spawn in summer mature at approximately age 3, and are the least migratory of the billfishes. However, results are in conflict concerning sex ratio and whether sailfish are single or multiple spawners. Although many researchers have reported that sailfish are sexually dimorphic, their fragile otoliths make them difficult to age, aging studies have not been validated, and sexual dimorphism has not been adequately separated from differences in age at first maturity. Life history studies are further compromised because identification of early life history stages is difficult and effect of genetically distinct stocks on these studies is unknown. Molecular markers representing a range of genetic resolution were used to investigate the genetic stock structure of the sailfish within and between oceans and to discriminate sailfish from other istiophorid billfishes. to investigate the genetic basis of stock structure, a 1700 by region of mitochondria) DNA which included the control region, was surveyed with five restriction endonucleases and representative individuals were sequenced. In addition, five nuclear microsatellite loci were assayed. Approximately 647 sailfish were collected from throughout the species' range over a six-year period from the Atlantic, Pacific, and Indian Oceans. Both mitochondrial and nuclear markers found that Atlantic, eastern Pacific, and Indo-west Pacific sailfish represent distinct genetic stocks. In addition, mitochondrial data revealed the presence of diverse clades, which were probably formed during Pleistocene glaciation. Independent molecular markers based on mitochondrial and nuclear DNA were developed to provide positive identification of istiophorid and xiphiid billfishes. Both classes of markers are based on amplification of short segments (<1.7 kb) of DNA and subsequent digestion with informative restriction endonucleases. ND4 and MN32-2, the selected markers, allow unambiguous specific identification, although it was not possible to differentiate white marlin and striped marlin. The resulting keys provide two independent means for the forensic identification of fillets and for specific identification of early life history stages.

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Squaloids (Order Squaliformes) are a highle diverse group of mostly deepwater habitats (> 200 m). Many species are regularly caught in commercial fisheries worldwide but their low productivity and correspondingly low intrinsic rebound potentials make them particularly vulnerable to population depletion and overexploitation. of special concern to fisheries management and conservation efforts are the spiny dogfish Squalus acanthias, the leafscale gulper shark Centrophorus squamosus and the Portuguese dogfish Centroscymnus coelolepis. These taxa have recently been declared overfished in several parts of each species' distribution but management efforts have been made to recover the "stocks" without a good understanding of the species' population structure and the level of connectivity among populations. as such, the goal of this dissertation is to elucidate the intraspecific patterns of population structure of each species, for future inclusion in fisheries management efforts, and to infer the patterns of historical dispersal of the three species of squaloid sharks. to this end, I have developed a suite of highly polymorphic molecular markers (including nuclear microsatellites and nucleotide sequences of mitochondrial DNA gene regions) and have collected tissues samples from throughout each species geographic range. The genetic population structure of S. acanthias was characterized by high genetic divergence across the equatorial Pacific, and by comparatively higher genetic homogeneity among the sample collections from the South Pacific and Atlantic oceans. Nevertheless, small but significant genetic differentiation was detected by both nuclear and mitochondrial markers among spiny dogfish collections from either side of the equatorial Atlantic. Genetic differentiation in the spiny dogfish occurred across low latitude regions characterized by warm-temperate and tropical waters, suggesting that such regions may act as effective barriers to gene flow among populations. Regarding C. coelolepis and C. squamosus, the pattern of genetic population structure uncovered for the eastern Atlantic was similar between species. Within this region, no evidence of genetic differentiation was found among sample collections ranging from off Ireland to South Africa, and including the Azores, consistent with the existence of a single genetic stock for each species within the sampled region. Furthermore, evidence for inter-oceanic dispersal between Atlantic and New Zealand populations was also found for the leafscale gulper. These results strongly suggest that both C. coelolepis and C. squamosus have high dispersal potential and no major barriers to gene flow within the deep eastern Atlantic. Overall, high genetic homogeneity was observed over large geographic areas (i.e. in the order of thousands of miles) in all three target species consistent with long-distance dispersal with gene flow. However, there were differences between the coastal and the deepwater squaloids regarding the regions of genetic discontinuity, which may be associated with adaptations to their respective habitats. In the coastal spiny dogfish, environmental factors such as unsuitable water temperatures appear to exert a strong influence in the species' distribution and in its genetic population structure. In the deepwater squaloids, stable environmental conditions but limited food supply may result in widely distributed populations as a strategy to maximizing resource partitioning while minimizing resource competition among individuals.

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Panulirus argus Virus 1 (PaV1) is an emerging disease in Caribbean spiny lobster Panulirus argus. It is considered a threat to the lobster industry in the Florida Keys. In order to understand the infection dynamics of the PaV1 virus in the lobster host, a sensitive and specific fluorescence in situ hybridization (FISH) assay was developed for diagnosis of PaV1 in lobsters. The lower limit of detection using the 110-bp DNA probe in a dot-blot hybridization for PaV1 was 10 pg of cloned DNA template and 10 ng of genomic DNA extracted from hemolymph of diseased spiny lobster. The probe specifically hybridized to PaV1-infected cells in all the tissues tested. The probe did not hybridize with host tissues of uninfected spiny lobsters, nor did it cross-react with other virus samples tested. A primary culture of hemocytes was developed for in vitro study of PaV1. The modified Leibovitz L-15 medium supported the best survival of hemocytes in cultures. Hyalinocytes and semigranulocytes maintained higher viability (∼ 80%) after 18 days when cultured separately. Hyalinocytes and semigranulocytes were susceptible to PaV1 in vitro. Cytopathic effects (CPE) were observed as early as 12 h post-inoculation, followed by cell debris and cellular exudates in inoculated cultures. This assay was further developed to assess viral load in hemolymph of diseased lobsters using a 50 tissue culture infectious dose assay (TCID50) based on CPE. The histopathology and hematology of the spiny lobster infected with PaV1 were studied over time courses of experimental infection. The fixed phagocytes in the hepatopancreas were the primary site of PaV1 infection in spiny lobsters. Infection was subsequently observed in the hepatopancreas, gill, heart, hindgut, glial cells around the ventral nerves, as well as in the cuticular epidermis and foregut. as the disease progressed, the hepatopancreas became significantly altered, with hemal sinuses filled with massive amounts of cellular aggregates, including infected circulating hemocytes and a proliferation of infected spongy connective tissues. The virus caused significant decreases in total hemocyte density in later stages of infection and significantly altered several constituents in the hemolymph serum of diseased lobsters, including: glucose, phosphorus, triglycerides, and lipase.

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No description available.

Allee effects occur when fitness suffers at low population size or density. This can lead to reduced population growth rate and a critical density below which extinction occurs. Allee effects can occur in reproduction or survival. Critical densities are higher in reproductive Allee effects than in juvenile survival Allee effects, making reproductive Allee effects more severe (higher extinction probability). In terms of the critical Allee effect threshold, reproductive Allee effects are more severe in r-selected populations, while juvenile survival Allee effects are more severe in K-selected populations. For populations with negative density dependence, there is a maximum critical Allee threshold, above which a population of any density goes extinct. Critical thresholds are altered by changes in mortality, such that Allee effects can interact with exploitation to cause non-linear population collapse. Adding two Allee effects together has unpredictable consequences depending on the life history. Adding negative density dependence makes Allee effects more severe. I tested Allee effects in the field in the queen conch Strombus gigas, a marine gastropod. Mating and egg production are reduced in low-density areas. This could be due to low encounter rates, habitat quality or ontogenetic differences. to distinguish between these hypotheses, mature conch were translocated between high and low density sites. Conch were at equal high density in all enclosures, but high source-site density produced higher reproductive activity. Conch from high-density source sites also had thicker shell lips, indicating that they were older. These data reject the hypothesis of an Allee effect; possibly reproduction is delayed after morphological maturity. In model simulations, a reproductive Allee effect and delayed reproduction could both produce non-linear population collapse. I show that predators can generate an Allee effect in prey if they have a Type II functional response and the aggregative or numerical response is not Type III (or vice versa). A literature review reveals several unrecognised examples of predation-driven Allee effects from the literature. This mechanism for Allee effects does not arise from the specifics of prey life history, which makes it difficult to predict and prepare for.

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The Asian clam, Corbicula fluminea, is one of the most invasive bivalves in the world but there is limited research on its presence in tidal freshwater systems. Despite its introduction into Chesapeake Bay tributaries in the 1970s, the initial colonization and subsequent development of populations of C. fluminea in the Mattaponi and Pamunkey sub-tributaries of the York River, Virginia, is mostly undocumented. This study assessed the spatial distribution and population structure of C. fluminea in tidal freshwater sections of these rivers (~45km) with benthic surveys during summer 2011 – 2012. Benthic grabs (2.4L, 0.023m2) taken at 40 sites in each river were analyzed for clam abundance and size. In addition, relationships between abiotic factors and clam distribution within each river were evaluated using Akaike’s Information Criterion (AIC) to compare a set of generalized linear models. C. fluminea was present at the majority of sites in both rivers during both years, with mean densities (m-2) during 2011 and 2012 of 660 and 410 for Mattaponi River; 1,451 and 834 for Pamunkey River. Populations were dominated by > 90% juvenile clams (< 6mm shell length), which is common for C. fluminea populations during recruitment periods. Both rivers had lower abundance during 2012, suggesting that C. fluminea is actively reproducing but not necessarily accumulating in the system. High juvenile and adult mortality are characteristic of C. fluminea populations. Compared to other invaded systems, C. fluminea in Mattaponi and Pamunkey Rivers is a low-to-moderate level invasion based on clam density. Using AIC analysis, the bestsupported models included factors of distance upriver (km), % sand, depth (m), and year. Distance and % sand showed positive relationships with C. fluminea abundance and had significant parameter estimates in all models (" = 0.05). Spatial analysis in GIS showed 3 that C. fluminea was widely distributed throughout the rivers but achieved higher densities further upriver and in sandier habitats. Despite these trends, Corbicula densities were highly variable, highlighting eurytopic habitat preferences of this species that have led to its successful invasion of tidal freshwater habitats. Populations may also be controlled by the high degree of physical disturbance in tidal freshwater systems and predation by fish and waterfowl.