Here today, gone tomorrow: flow variability, larval dispersal and fisheries management in Hawaiʻi
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2012-12
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University of Hawaii at Manoa
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A contemporary challenge in marine ecology is understanding population connectivity driven by transport during early life stages. Connectivity results from a complex combination of biological traits and physical mechanisms. This dissertation begins by investigating the influence of physical mechanisms on particle transport around the Island of Hawaiʻi. Particle dispersion was determined by using an individual-based model (IBM) and the flow fields derived from a global and a regional implementations of an ocean circulation model. To understand the underlying physical processes of transport, coherent structures were located in the flow field, recurrent physical features were identified, and how particle transport related to them was observed. Results showed that the eddying flow increased connectivity and influenced retention, as well as that both the flow field and dispersal patterns were highly variable. In this scenario, eddy events influenced transport in distinct ways, and the timing of release played an important role in the dispersal and resulting connectivity. Differences were found in the transport of particles and emerging connectivity patterns when comparing the two model implementations, highlighting that modeling studies should use hydrodynamical model flows representing the scales of variability affecting dispersion. Then, the IBM was adapted for fish species, and connectivity patterns along the Hawaiian Archipelago of three bottomfish: E. coruscans, E. carbunculus, and P. filamentosus were investigated . These species appeared to share common features in their connectivity patterns driven by larval transport, as follows: i) limited connectivity between the Papahānaumokuākea Marine National Monument (PMNM) and the Main Hawaiian Islands (MHI); ii) greater connectivity among islands in the PMNM than in the MHI; iii) existence of four, mostly self-contained, dispersal zones along the Archipelago; and iv) islands from Kauai to Necker connected the PMNM and the MHI through larval dispersal, acting as ecological corridors. When the MHI's bottomfish restricted fishing areas (BRFAs) were considered, it was found that these reserves are potentially replenishing depleted fishing areas by larval export, but rely on larval subsidy from the fishing sites to sustain their populations. Thus, the efficiency of the reserve network could be improved by the protection of additional bottomfish habitat, distributed in new or expanded reserves. Finally, dispersal characteristics of yellowfin tuna (T. albacares) around the MHI were investigated. The physical environment appeared favorable for retention of yellowfin tuna larvae. However, retention is not the main factor optimizing the spawning season of this species in the archipelago, and other factors, such as favorable water temperature and food availability, are likely contributing to spawning seasonality. The distribution of larvae by the time evolving eddying field was highly variable. Apart from nearshore regions, no additional persistent dispersal pathways or accumulation zones were observed.
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Lagrangian Coherent Structures, larval dispersal, eddy variability, reserves
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Oceanography.
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