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Toothed whales produce regular echolocation clicks to sense their surroundings and hunt. These clicks can be detected on hydrophones allowing researchers to study and monitor animals, a methodology known as passive acoustic monitoring (PAM). PAM methods can be used to detect behaviours such as foraging, calculate the absolute abundance and determine the 3D positions of soniferous animals. However, this requires robust detection, species classification and localisation algorithms alongside a statistical framework to estimate animal density. Detection, classification and localisation methods were developed to obtain fine scale behavioural information of toothed whales which was then integrated with a distance sampling-based framework to estimate density. These methods were applied to calculate the behaviour, 3D distribution and density of harbour porpoises in a tidal stream habitat. Toothed whales produce clicks in sequences (clicks trains) which can provide information on behavioural state and aid in species identification. A click train detection algorithm was developed to extract these sequences and performance then tested on PAM data from sperm whales, delphinids and harbour porpoise datasets. Localisation in tidal rapids is difficult due to fast moving currents and high densities of toothed whales producing a complex soundscape. A drifting free-hanging vertical hydrophone array with movement sensors, click aliasing and track association algorithms was developed to collect geo-referenced 3D tracks of toothed whales in tidal streams. The full 4π beam profile of a free-swimming captive harbour porpoise was measured. This showed that harbour porpoises have significant acoustic energy at extreme off-axis angles (>30°) which has implications for detectability on PAM devices. Drifting sound recorders and vertical hydrophones arrays were used to survey a tidal rapid site. Detected click trains, dive data and the measured beam profile were used to inform simulations of detection probability of harbour porpoise clicks and calculate animal density and foraging rates.

Bottlenose dolphins (Tursiops truncatus) produce a wide variety of sounds but little is known about the function and organization of their vocal repertoires. This thesis investigates several aspects of call usage and compares the biological validity of classification methods for dolphin whistles. Passive acoustic localisation methods were used to identify which animal produced a sound. Observations of captive dolphins in the Zoo Duisburg, Germany, showed that signature whistles are almost only used when the group was split up, but not if all animals swam in together in the same pool. This finding supported the hypothesis that signature whistles are cohesion calls. Whistles from these observations were used to compare whistle classification conducted by eye with three computer methods using different similarity measures. Only the human observer classification was able to recognize whistle types that were used in a context- specific way by the animals confirming the power of this common classification method. Copying of signature whistles and whistle matching between animals was rare in captivity. However, observations of whistle interactions in the Moray Firth, Scotland, showed that wild dolphins do not tend to interact vocally in general, but that whistle matching was more frequent than expected by chance. Whistle matching in captivity was rare. Sound pressure measurements of dolphin whistles in the wild showed that source levels can reach up to 169 dB re 1 ?Pa and that the active space of a dolphin whistle can range up to 38 km. Finally, observations of foraging in wild dolphins revealed that they produce low frequency braying sounds in this context. Other dolphins would rapidly approach the caller in response to a bray. However, it is not clear whether brays function to attract conspecifics or manipulate prey behaviour.