Habitat preferences and movement patterns of bottlenose dolphins at various spatial and temporal scales
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Date
2019
Authors
Garagouni, Maria
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University College Cork
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Abstract
Quantifying marine mammal abundance, site occupancy, and habitat use patterns is fundamental for the correct design and implementation of conservation and management schemes. Bottlenose dolphins in Irish waters form at least three distinct populations, two coastal and one pelagic, each ranging in different areas over unequal scales. While the abundance of all three has been estimated and core areas of use have been previously identified for the coastal populations, their habitat preferences have not yet been investigated sufficiently. In this thesis, generalised additive models were used to describe the habitat use of each population in relation to a suite of static and dynamic environmental parameters, over a range of temporal scales. Mixed models and generalised estimating equations were implemented to account for spatial and temporal autocorrelation when necessary. The habitat use of the pelagic population was modelled using two seasons (Summer and Winter) of aerial survey data of the greater part of the Irish EEZ and the models’ predictive capacity was tested on observations from two separate seasons. The interaction of environmental covariates with a habitat classifier was also tested to elucidate dolphin habitat use changes depending on whether they are in shelf, slope, or abyssal waters. The site occupancy of the coastal mobile population was modelled using five years of passive acoustic monitoring (C-POD) data from two locations on the west coast at an hourly, daily, and monthly scale. The second coastal population is resident in the outer Shannon estuary Special Area of Conservation and its abundance has been sporadically monitored for nearly two decades using boat-based photo-identification surveys. Encounter data from these surveys were used to model habitat use by incorporating a two-dimensional geographic coordinate term and an interaction with tidal phases. Given the irregular frequency of standardised surveys, I also assessed the potential of using a dolphin-watching boat operating in the same area as an alternative platform from which to derive a robust abundance estimate, using mark-recapture techniques. Different environmental covariates proved significant at each spatial scale, with dolphins showing season-, habitat-, and site-specific responses to each parameter. A higher probability of dolphin presence was predicted over the continental shelf and slope in the winter and in two primary areas in the summer, the southwest coast and the Porcupine Basin. Sea surface temperature and primary productivity were significant predictors of dolphin presence for both the pelagic and mobile coastal population, but not for the resident coastal population. Tidal level had a significant effect on dolphin detection in the coastal mobile population, with the likelihood of detections increasing at higher water levels. Tidal phase was also a significant predictor of dolphin presence for the resident population, with higher probabilities being predicted closer to a bottleneck feature during ebb tides. The abundance estimate generated from the dolphin-watching boat observations compared favourably to an estimate generated from a standardised survey the previous year. This indicates that, in years when standardised surveys do not take place, the dolphin-watching boat may provide a suitable interim platform for more frequent and efficient monitoring of this population. The results presented here highlight the importance of investigating habitat use at different spatial and temporal scales, provide valuable insights regarding areas used at different times by bottlenose dolphins, and form a baseline upon which to build further, more targeted investigations of the habitat preferences, demographic parameters, and abundance of each population, ultimately advancing our efforts at conservation and facilitating marine spatial planning.
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Keywords
Bottlenose dolphins , Tursiops truncatus , Habitat use , Habitat models , Abundance , Mark-recapture , Photo-identification , Irish EEZ , Shannon Estuary , Platform of opportunity , Passive acoustic monitoring , Site occupancy , Generalised additive models
Citation
Garagouni, M. 2019. Habitat preferences and movement patterns of bottlenose dolphins at various spatial and temporal scales. PhD Thesis, University College Cork.