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Title: Multitrophic investigations of the pelagic marine ecosystem of the Clyde Sea
Author: Lawrence, Joshua M.
ISNI:       0000 0004 7972 5468
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2019
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Knowledge of where animals are and why they are there is central to our understanding of their ecology and is essential for the successful management of vulnerable species. Harbour porpoises, the most abundant cetacean in European waters, are protected under EU law due to their vulnerability to a range of anthropogenic treats. Significant effort has been put into describing and understanding their distribution, but very little of this effort has included fine resolution, simultaneously collected data on the distribution of their prey species, potentially limiting the biological relevance of the conclusions drawn. The aim of this thesis was, therefore, to use the simultaneous sampling of the distributions of porpoises and species at lower trophic levels to be able to better understand and explain the observed predator distributions. Methods were developed for the concurrent collection of passive acoustic data, detecting harbour porpoise echolocation clicks, and active acoustic data, for the detection and quantification of clupeid fish and macrozooplankton. Implementing these methods during three annual surveys in the Clyde Sea, off Scotland's west coast, provided data on the distribution of these species, which could be used to investigate the spatial relationships between their distributions. The distribution of porpoises was found to be significantly related to that of their clupeid fish prey, with a higher detection rate expected in areas with higher fish density, along with geographic and hydrodynamic variables. The distribution of clupeid fish was in turn related to the distribution of macrozooplankton, with more fish found in areas with higher zooplankton densities, as well as a range of environmental variables. The scale at which these relationships were found to be strongest differed between species pairs, with the link between porpoises and fish being stronger at longer distances than that between fish and zooplankton, most likely due to the relative motilities, sensory capabilities, and behaviours of the species involved. The current state of the study system, which has been subject to heavy anthropogenic exploitation, was also described, presenting biomass and abundance estimates for the main species across three trophic levels. A notable shift in the dominant forage fish species from herring to sprat was observed, by comparison with similar active acoustic surveys in the late 1980s. The value of concurrent sampling of predators and prey was demonstrated, and the work present here has added to our understanding of the drivers of the distributions of a cetacean top predator and the forage fish assemblage in an impacted marine ecosystem.
Supervisor: Fernandes, Paul George ; Scott, Beth Emily Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Cetacea ; Marine mammals ; Marine ecology ; Marine biology ; Sound