Behavioural responses by seals to offshore energy activities

Abstract

To effectively manage interactions between industrial activities and wildlife populations in increasingly urbanised environments, it is essential to understand how animals may be affected by different anthropogenic activities. In this thesis, I used biologging devices to investigate the potential effects of sound disturbance on seals. By simulation study, I evaluated the use of statistical tools (Mahalanobis distance) to detect unusual instances of movement and dive behaviour in seal biologging data. The results of these simulations were used to produce recommendations for future studies aiming to detect behavioural changes in animal movement data. Building on the findings of this work, I examined the movement and dive behaviour of 24 harbour seals (Phoca vitulina) during pile driving construction at an offshore wind farm in the UK. Using GPS location data collected on animal-borne tags, I identified statistically unusual horizontal movement events during pile driving, typically consisting of increases in speed, the cessation of horizontal movement, or the sudden initiation of travel. Using dive data from animal-borne tags, I identified statistically unusual groups of dives, and also characterised the effect of pile driving activity on behaviour-switching between different dive types (by hidden Markov models). Seals were found to switch dive behaviours more often during pile driving (compared to baseline periods), and the identified unusual dives were typically shorter and shallower, with longer post-dive surface intervals. For both horizontal and diving responses, dose-response curves were produced to estimate the relationship between the received sound level of pile driving and the probability of a behavioural change. By examining behaviour at the individual-level, improved insights of at-sea seal behaviour during disturbance events were gained. The results of this thesis also inform future offshore activities, enabling the renewable energy industry to develop in a timely and environmentally-responsible manner.