Large-scale and long-term passive acoustic monitoring of coastal bottlenose dolphins

Abstract

Bottlenose dolphins in eastern Scotland are a protected and wide-ranging population exposed to a variety of stressors throughout their available habitat. Previously, most studies have focused effort on areas where animals are known to congregate. These areas are easily accessible and cost-effective for visual surveys. However, there is a need to understand the behaviour and habitat use of the population throughout its habitat. In response to this need, the Scottish Government initiated the East Coast Marine Mammal Acoustic Study consisting of 40 passive acoustic monitoring devices deployed along the coastline. While acoustic loggers are a cost-effective way of collecting longitudinal information, the returned data are subject to fluctuating detection probability and species misclassification. Subsequently there are two aims in this thesis. First, I seek to validate the use of autonomous detectors in large- scale and long-term studies where multiple species are present. This includes building a classifier to discriminate between groups of acoustically dissimilar species and investigating how transmission loss and ambient noise could bias occupancy results. Second, occupancy data from the array are analysed in order to understand spatial and temporal trends in habitat use and behaviour. The outputs of this thesis include an acoustic classification system capable of increasing the taxonomic resolution achievable in autonomous logger outputs and a framework for investigating detection probability in a complex acoustic system. The resulting habitat models were consistent with previous surveys showing that that depth and distance to the coast were important predictors for bottlenose dolphin presence. Finally, I found differing patterns in diel activity between a known foraging location and habitat not associated with foraging. Results from this thesis will provide tools for future researchers seeking to use passive acoustic monitoring techniques as well as baseline information about bottlenose dolphin habitat use and behaviour across the Scottish coastline.