Gene flow is an integral biological process that can mediate speciation. While many consider the ocean to be an open environment, there are many barriers that limit gene flow, particularly in the western Atlantic. I analyzed data from two widespread, coral reef fishes, the bridled goby (Coryphopterus glaucofraenum) and sand-canyon goby (C. venezuelae), throughout their range in the western Atlantic. Using two genetic datasets, mitochondrial DNA (mtDNA) and genomic SNPs, I investigated the evolutionary history of these species and inferred the location and strength of putative barriers. My results suggest that several unique lineages have genetically diverged from one another in the presence of two major barriers. First, the Amazon River has isolated Brazil from the Caribbean and second, a unique lineage was found at an isolated oceanic island, Atol das Rocas, off the northeast coast of Brazil. Furthermore, minor barriers have caused slight genetic differentiation in each of the Caribbean species off the coast of Venezuela, while on the Brazilian coast, there are up to two barriers that separate three genetically unique areas. The stronger of the two barriers is located at Cabo Frio near an upwelling system and the weaker barrier coincides with the outflow of the São Francisco River. Overall, this research highlights how barriers impact speciation and genetic structure within these gobies in the western Atlantic and more broadly, deepens our understanding about the role of oceanographic features in the speciation process.

North American amphibians have recently been impacted by two major emerging pathogens, the fungus Batrachochytrium dendrobatidis (Bd) and iridoviruses in the genus Ranavirus (Rv). Environmental, seasonal and host factors may play important roles in disease dynamics, but few studies incorporate these components into their analyses. Here, we investigated the role of environmental, seasonal, genetic and location effects on driving Bd and Rv infection prevalence and severity in a biodiversity hot spot, the southeastern United States. We used quantitative PCR to characterize Bd and Rv dynamics in natural populations of three amphibian species: Notophthalmus perstriatus, Hyla squirella and Pseudacris ornata and more broadly in multi-species amphibian communities across Florida. We combined pathogen data, genetic and host metrics, and seasonal and environmental variables into statistical models to evaluate how these factors impact infectious disease dynamics. Occurrence, prevalence and intensity of Bd and Rv varied across species, populations, and sites. Pseudacris ornata was found to have high levels of Bd across sites. In Florida, both pathogens were found ubiquitously across sites and seasons and at high levels within three different host families. We conclude that Bd and Rv are more abundant in the southeastern United States than previously thought and that host, seasonal and environmental factors are all important for predicting amphibian pathogen dynamics. Incorporating seasonal, host and environmental information into conservation plans for amphibians is necessary for the development of more effective management strategies to mitigate the impact of emerging infectious diseases.

Research into species inhabiting Benguela current region has been the southern part biased towards of those the of commercial importance and accessible than others. A those which are either more visible or crude evaluation of material flows and standing stocks, including the lesser studied species, was made. Estimates suggest that the productivity of juvenile hake C3 million metric tonnes per year or more, squid(> 0. 5 million metric tonnes per yearly, and midwater shoaling fish (together > 0. 5 million metric tonnes per year) is substantial compared to the total annual landing of marine fish off South Africa which is in the region of 0. 5 million metric tonnes. The consumption of anchovy and other epi-pelagic shoaling fish is dominated by piscivorous fish, particularly snoek. Snoek may consume as much as 0. 4 million metric tonnes of anchovy per year, out of a total anchovy production of in the region of 2 million metric .tonnes wet mass per year. Anchovies are the main fish consumers of plankton, with an estimated consumption of more than 20 million metric tonnes wet mass per year. Total annual plankton production is in excess of 800 million metric tonnes wet mass. About 32% of this enters higher trophic levels in the epi-pelagic region, mainly through zooplankton grazing. It is suspected that the bulk of production in the zooplankton and hake communities is recycled by omnivorous feeding in the case of zooplankton and cannibalism in the case of hake. The amount of cannibalised hake is about 10 times the amount taken by trawlers. The biomass, production, and consumption rates of apex predators such as seals, whales, dolphins and seabirds (sizes of the order of metres to 10' s of metres) is quantitatively unimportant in comparison with species consisting of smaller individuals (sizes of the order of 10's of centimetres). Due to the complexity of the food web, a conceptual model based on size may be preferable to one involving trophic levels. Overall, however, the complexity of the system, and the sketchiness of knowledge about it mitigates against the use of multispecies models for making useful predictions. A maximum likelihood estimation approach to Virtual Population ·Analysis ( VPAl is adopted, developed, and implemented. It is shown from results obtained using artificial fisheries data that the database conventionally considered adequate for VPA work, viz. the catch mass and age structure, does not lead to reliable estimates of stock abundances for recent years. Use of further data related to stock adundance, such as effort data in situations where catch per unit effort is proportional to abundance, is investigated. Results using simulated effort data show dramatic improvements in abundance estimator precision~ It is therefore argued that VPA should not be attempted in the absence of data complementary to the catch masses and age structures. With this in mind, VPA is applied to three stocks of commercial importance which occur off the South African coast 1 i ne: anchovy, pi 1 chard and hake. Results are presented which show that anchovy biomasses are determined with reasonable precision if catch rates can be assumed to be proportional to stock abundance, and if the selectivity functional form is known. However, it is argued that it is unlikely that catch rates are proportional to anchovy abundances. Furthermore, recent surveys of the anchovy stock size and habitat range suggest that the relationship between age and selectivity is different to that used in the analysis and is essentially unknown. Accordingly further analyses are performed, excluding the _ effort data, and replacing the initial one parameter selectivity function with unique selectivity parameters for each age class seen in the catch. Very imprecise biomass estimates are obtained when the likelihood function is formulated in this way, due to the now enhanced instability of the position of the maximum of the VPA likelihood function. Separate simulations illustrate that the bias in abundance estimates introduced by using the same age length key in all years for converting catch length distributions to catch age distributions may be as much as 50%. This, the aforementioned imprecision of VPA biomass estimates, unassessed but probable errors in the single age length key, which is used, and finally very recent ageing re-evaluation studies suggesting that the catch consists almost entirely of 0-year-olds, effectively rule out the possibility of obtaining management-orientated information from the anchovy VPA. Complementary data for the pilchard VPA is obtained by analysis of records of guano harvests which are made at a number of islands off the South African coastline. Evidence is presented suggesting that the harvest at Bird Island, Lambert• s Bay is approximately linearly related to pilchard recruitment and these guano harvests are thus included in the likelihood function for the pilchard VPA. The resultant biomass estimates are plausible in terms of the likely system carrying capacity for pelagic fish. The biomass trend does not reflect the major peak in biomass in 1960 which earlier work consistently suggested. An appropriate sum of squares _minimisation procedure is adapted from the LudwigWal ters' formulation for fitting the pilchard stock recruit function to the recruitment and spawning biomass data from the VPA. The surplus production curve is estimated by combining the estimated recruitment function parameters with a yield per recruit analysis. The results indicate a mean virgin spawning biomass of 2. 4 million metric tonnes, and an MSY spawning biomass level of 1. 0 million metric tonnes. The maximum sustainable annual catch, for a 20 -year scenario starting with the population at half the unexploited biomass and ensuring a 10% maximum risk of obtaining a stock size of less than 0.2 of the pristine size, is 187 thousand metric tonnes. The surplus production curve for the hake stock off the west coast of South Africa C ICSEAF Div. 1. 6> is estimated using the same methods as applied to pilchard. No substantial difference between the VPA results and those produced using dynamic catch effort models could be demonstrated - both VPA and the Schaefer model predict a maximum sustainable yield of about 140 thousand metric tonnes. Closer analysis shows however that the additional age structure information taken into account by the VPA has not led to better estimates than are provided by the catch mass and effort data alone. The suspected past practice of discarding small hake at sea potentially invalidates all sustainable yield calculations, even those based on the dynamic catch-effort models, by introducing spurious effects into the catch-based statistical records. The future in hake stock assessment may therefore lie with Casis the case for the pelagic species> direct survey techniques.

Introduced cichlid species are increasingly more common in tropical freshwater systems and expanding in range, often with negative consequences to receiving systems. To better understand, monitor, and manage these populations, improved cichlid sampling protocols are required. The goal of this study was to (1) evaluate diel electrofishing and gill netting sampling catch efficiency, and (2) compare two non-lethal methods for extracting stomach contents from Butterfly Peacock Bass Cichla ocellaris. This study suggests that electrofishing, particularly at night, may be a more appropriate gear for sampling cichlid species in the littoral zone of reservoirs, as gill nets were more time intensive, had more variable catch rates, and exhibited considerable selectivity. Pulsed gastric lavage was more effective than acrylic stomach tubes for extracting stomach contents from Butterfly Peacock Bass and was less injurious, with bruising of the stomach wall the most common injury being observed.

No description available.

No description available.

No description available.

Age, growth rates, and patterns of movement were studied in the Atlantic stingray, Dasyatis sabina, in the Indian River lagoon system in east central Florida. Age was estimated using the growth rings on the vertebral centrum and tretacycline marking. Tetracycline injections produced clear readable rings in all pups, but failed to be incorporated into the centra of adults. Females possess more centrum rings than males, but annual periodicity could not be verified. Growth rates were determined from aquarium held pups and adults and from tagged and recaptured animals. Males appeared to reach maturity in about two years, females in slightly less than three. Males and females probably reached mean size, 240 and 300 mm, respectively, in six to nine years. Movements of Dasyatis sabina were fairly restricted seasonally as well as annually; the majority (81%) of animals recaptured were taken at the release site. The general age and growth strategies for this species are consistent with those of most other elasmobranchs, characterized by rapid growth the first few years followed by slow adult growth.

The eastern oyster, Crassostrea virginica, once an integral part of the ecology and economy of Chesapeake Bay, has been severely depleted. Factors leading to the decline of the eastern oyster include over-harvesting, environmental degradation and disease pressure caused by the protozoans Haplosporidium nelsoni and Perkinsus marinus, known commonly as MSX and Dermo, respectively. Studies regarding the feasibility of introducing a nonnative oyster to the Bay were initiated, and field-based research on an Asian oyster, Crassostrea ariakensis, suggested that it might be a viable species for introduction. Research surrounding the proposed introduction has focused on recommendations such as those from the International Council for Exploration of the Seas, suggesting that the "ecological, genetic and disease relationships of the species in its natural range and environment" be examined. In order to assess the disease risks associated with C. ariakensis, a parasite survey of oysters collected from China, Japan and Korea was undertaken to examine the pathogens associated with C. ariakensis in its natural range. The protozoan parasites, Perkinsus olseni and a new Perkinsus sp., as well as multiple genetic strains of molluscan herpesvirus, were discovered using molecular diagnostic methods. Molluscan herpesvirus and Perkinsus spp. protozoans are known to cause mortality of many commercially important bivalve species. Characterization of the new Perkinsus sp. included a comprehensive analysis of three DNA loci along with histological examination of the Perkinsus sp. cells in preserved tissue sections. Challenge experiments were undertaken using P. olseni and the new Perkinsus sp. in order to assess the transmission risk of these exotic microbes to the eastern oyster and the hard clam, Mercenaria mercenaria. The laboratory experiments suggest that bivalve shellfish native to Chesapeake Bay may be susceptible to the alien Perkinsus spp. associated with C. ariakensis. In addition, C. ariakensis may acquire moderate to lethal infections of P. marinus under stressful conditions. In light of the proposed introduction of C. ariakensis, it appears that there is a great disease risk associated with this Asian oyster species with the potential to have a negative impact on the naive shellfish populations of Chesapeake Bay.

A size-selectivity curve was constructed to characterize the performance of the New Bedford style Atlantic sea scallop (Placopecten magellanicus) dredge when it is configured to meet the requirements of Amendment #10 to the Sea Scallop Fishery Management Plan. The curve was generated using the SELECT model on catch-at-length data, obtained by simultaneously towing a New Bedford style dredge and a non-selective National Marine Fisheries Service sea scallop survey dredge from commercial scallop vessels. Data were collected during three cruises in the Northwest Atlantic between 2005 and 2006. One cruise was completed in Georges Bank (Groundfish Closed Area II) and two cruises were completed in the mid-Atlantic (both in the Elephant Trunk Closed Area). The resulting selectivity curve for all cruises combined yielded a 50% retention length of 100.1 mm, a selection range of 23.6 mm and a relative efficiency value of 0.77. A length of 100.1 mm corresponds to an age of 4.6 years in Georges Bank and 5.8 years in the mid-Atlantic and a meat-weight of approximately 16 g. This implies that entry into the fishery is being delayed, potentially increasing yield-per-recruit and the population’s total reproductive output. The resultant selectivity curve can assist fisheries managers with stock assessments, mortality calculations and with the interpretation of catch data from government and industry-based surveys. Additionally, the curve can be used to evaluate the effect of future changes to sea scallop dredge design.