Browsing by Subject "Marine ecology"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Applying Fishery Catch Data to Population Trends and Community Structures in Atlantic Pelagic Species
    (2017-05-06) May, Eva
    Recent studies have shown that fishing can influence marine trophic networks, as larger, higher trophic level species are preferentially targeted by fishers. In this study, we investigate US Pelagic Longline catch dynamics of twenty-nine Atlantic species from 1986 to 2008 using information provided by the fishermen’s logbook data program. Two different analyses were performed on the data for this study. Data were cleaned and monthly catch per unit effort (CPUE) for each species within each of five fishing effort regions – the Mid Atlantic Bight and Northeast Costal area, The Caribbean area, the Florida East Coast and South Atlantic Bight area, the Gulf of Mexico area, and the Northeast Distant area – were calculated to examine trends in catch rates. Annual CPUE graphs were made for all areas combined, correcting for changes in fishing dynamics to examine changes in relative abundance of species over time. A regression was run through these annual graphs of CPUE over the study period in order to estimate increases or decreases in relative population abundance for each species. The slopes from these annual abundances regressions were further regressed versus trophic level, average generation length, and resiliency to test for significant correlations between these ecological factors and trends in population size. Though trends matched our predictions (species with higher trophic level, lower resiliency, and longer generation length showed greater declines in abundance), no significant p-values were found. It seems likely that ecosystem structural shifts similar to those seen in other recent studies are occurring, but the lack of significance makes it difficult to draw strong conclusions. The lack of significance between ecological factors and population trends observed in this study may be due to trophic shifts in fishing are not occurring or may be due to issues with the data used for regressions. Future studies using different methods of obtaining demographic factors and incorporating additional years of catch data could bring more clarity to this work.
  • Thumbnail Image
    ItemOpen Access
    Life History Analysis and Identification of Potential Nursery Grounds for Juvenile Manta Rays
    (2020-04-24) Werner, Nicholas
    Manta rays are zooplankton consuming filter-feeders that have a global distribution across tropical, subtropical, and temperate waters. There are two recognized species of manta – the Giant Oceanic Manta, Mobula birostris, and the recently resurrected Reef Manta, Mobula alfredi – as well as a putative third species, Mobula sp. cf birostris. Their conservative life history traits, including late sexual maturity, relatively long lives, and exceptionally low fecundity, increase manta vulnerability to environmental stressors and substantially diminish their resiliency. Currently listed as “Vulnerable” by the IUCN Red List, mantas are facing increasing anthropogenic pressure from targeted and bycatch fisheries that harvest their gill rakers for use in eastern medicine. Despite their perception as charismatic megafauna, much is still unknown about the biology, ecology, and life history of mantas, particularly relating to the juvenile life stage. Therefore, this research synthesized knowledge from published literature and identified a widespread lack of data, including glaring gaps regarding sexual maturation and fecundity, lifespan, and the occurrence of and mortality rates associated with natural predation. These gaps, and many more, were especially prevalent within non-adult life stages. From the available data, the following characteristics were isolated and sampled from a known manta ray nursery ground (Flower Garden Banks): water depth, water temperature, productivity, and proximity to deep water environments. These characteristics were applied within the Gulf of Mexico with limited results, though should form the basis for future, more in-depth studies.
  • Thumbnail Image
    ItemOpen Access
    Species Distributions in a Changing Ocean: from Individuals to Communities
    (2021) Roberts, Sarah

    Changing ocean conditions and biotic dependencies will influence commercially important species distributions in this interconnected and rapidly changing world. In this dissertation, I employ random forests, GAMs, and a generalized joint attribute modeling technique to study the impacts of climate, substrate, and fishing pressure on nearshore and pelagic species distributions and abundances in the North Atlantic. Through these approaches, I provide insights on which species have shifted environmental associations over time to more accurately model potential distribution shifts going forward. By comparing pelagic and nearshore species, I enlighten future modeling and management to the fact that not all species will behave the same in the face of a changing climate. By including fishing pressure in my models, I provide a better understanding of the relative effects of fishing pressure compared to climate on species distributions and abundances resulting in a more realistic and comprehensive understanding of the causes of shifting distributions. I utilize a joint modeling approach to help better inform the interspecific interactions that shape a species’ distribution. Finally, by modeling fishing gear as a species, I attempt to get us one step closer to an ecosystem approach to fisheries management.