Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item The Role of Connectivity and Spatial Structure on the Population Dynamics of Marine Fishes(2023) Arai, Kohma Herbert; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Migrations regulate population structure, which can play an important role in conferring stability at aggregate scales via asynchronous responses of population sub-components to perturbation; however, little is known about the importance of spatial structure in population persistence in fishes. My dissertation aims to explore the role of spatial structure on the population dynamics of marine fishes. Two species that exhibit different types of population structure were considered: (i) Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic, comprised of two components that have distinct spawning regions off Canada (northern contingent) and the US (southern contingent); and (ii) striped bass (Morone saxatilis) in the Hudson River (HR), which exhibit early-life partial migration whereby a portion of juveniles remain in their natal freshwater habitats, while others migrate into higher salinity habitats. In Chapter 2, I used otolith stable isotopes (d18O/d13C) to understand contingent mixing of the Northwest Atlantic mackerel over two decades (2000–2019). Prevalent contingent mixing occurred within the US waters, indicating that the northern contingent may provide subsidies to the US mackerel fishery. In Chapter 3, I combined machine learning with otolith d18O isoscapes to predict the geographic origin of the Northwest Atlantic mackerel spanning four decades (1975–2019). Contingent mixing occurred over four decades, including the 1970s when intensive foreign fisheries took place in US waters. Nursery hotspots were detected within spawning regions, but shifted over time. In Chapter 4, for HR juvenile striped bass, I explored the influence of early-life conditions and environmental drivers on partial migration. Otolith chemistry uncovered four dominant early migration modes. Partial migration was associated with larval growth, albeit facultatively controlled by environmental conditions. In Chapter 5, I evaluated how HR striped bass early-stage partial migration influenced recruitment patterns to the adult population over a 3-decade span. As an outcome of partial migration, adults recruited from a variety of nurseries, which exhibited asynchronous dynamics in response to climate variables. Through a comparative analysis of two species that exhibit different types of population structure, I demonstrated how spatial structure can play key roles in the population dynamics of marine fishes, with implications for management and conservation.Item Evaluating the Consequences of Alternative Atlantic Striped Bass Harvest Control Rules on Their Prey, Atlantic Menhaden(2022) Schiano, Samantha E.; Nesslage, Genevieve; Wilberg, Michael; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Harvest control rules (HCRs) are automatic fishery management procedures that are agreed upon in advance and that dictate the rate of fishing that can take place. I evaluated a suite of single species and dynamic multispecies HCRs to evaluate their relative performance in achieving management goals for the striped bass (Morone saxatilis) and Atlantic menhaden (Brevoortia tyrannus) stocks using a linked, age-structured predator-prey simulation model. First, simulation model inputs were updated using the most recent stock assessment information, and striped bass length- and weight-at-age estimates were updated using otolith-based ageing data. Linear models evaluating change in striped bass length- and weight-at-age over time and between sexes identified an increase in size of as much as 30% between 1998 and 2019. Additionally, striped bass continued to grow past age-15, indicating that future striped bass stock assessments should consider expanding the number of ages included in the model. The updated predator-prey simulation model was then used to compare performance of a suite of 27 HCRs. The most influential factor determining performance of striped bass HCRs was striped bass fishing mortality (F). Atlantic menhaden had little effect on striped bass spawning stock biomass (SSB) at both high and low percent composition of Atlantic menhaden in striped bass diets. Traditional single species HCRs performed well, specifically those for which striped bass are managed at or below their target F. Although there was no single HCR that performed well for both stocks given their current reference points, both single species and dynamic multispecies HCRs that involved the “40-10 rule” for striped bass (lower threshold at 10% of unfished SSB and upper threshold at 40% unfished SSB) performed best across all striped bass performance metrics.