THE ECOLOGY AND CONSERVATION OF THE HARBOUR PORPOISE (PHOCOENA PHOCOENA) ALONG THE WEST COAST OF THE UK

Abstract

Whilst the harbour porpoise {Phocoena phocoena) is the most j&equently observedcetacean in the UK, it. is at risk from habitat degradation, pollution, incidental capturein fishing nets and anthropogenic disturbance. UK, European and Internationalinitiatives have highlighted the conservation need to obtain a better understanding ofthis species. This research, conducted over 5 years (1999-2004) aimed to fiirther thescientific knowledge of the harbour porpoise in order to influence fiiture conservationinitiatives. Studies into the relative abundance, density, distribution, habitat use andbehaviour were conducted through combinations of shore- and boat-based research.Technical trials of a towed acoustic device (T-POD) were also conducted fromonboard the research vessel. Additional analysis of previously collected acoustic datafrom bottom-set gillnets was carried out This research presents some of the firstexamination of the west coast for the harbour porpoise. Porpoise density was found tobe exhibit significant inter-anniial differences, with increases noted off West Scotiandand a decrease observed for the South West In the case of Northern freland theseresults are some of the first quantitative analysis of the harbour porpoise within theregion. A statistically significant relationship with depth and in particular the 100mdepth contour was also observed. The area off north Devon (Morte Point) isconsidered to offer an important feeding site for the species, where porpoises werefound to aggregate in areas of high tidal flow. Site-specific differences in behaviour,group size and distance from shore were observed depending on time of day and tidalcycle. A full description of the ethology of the harbour porpoise is also given and the potential affects of dolphin watching tourism assessed. Porpoises were observed toregularly engage in cooperative feeding and aerial activity, previously consideredrare. The behaviours, as recorded from shore, differed considerably to those recordedfrom the boat. This highlights the need for precautionary management to increasingnumbers of dolphin watching tour operators in UK waters. Acoustic detection ofharbour porpoises around bottom-set gillnets revealed that porpoises are presentaround the nets on a 24 hour basis. This is highly significant in terms of bycatchmitigation as it indicates that porpoises are successfiilly avoiding entanglement for99.75% of encounters. In terms of monitoring populations the T-POD was found topresent a cheap and quick method which detected an additional 10% of all porpoiseencounters which were not detected visually. The results presented here make asignificant contribution to the scientific knowledge of the harbour porpoise, whichwill provide a basis for future research and conservation initiatives.

Date of Award	2007
Original language	English
Awarding Institution	University of Plymouth
Supervisor	Pete Cotton (Director of Studies (First Supervisor)), Martin Attrill (Other Supervisor) & N. Tregenza (Other Supervisor)