Restriction lift date: 2025-09-30
A multi-method approach to understanding the ecology of harbour porpoise in Irish waters
Loading...
Files
Date
2023
Authors
Todd, Nicole R. E.
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
Small coastal cetaceans are often some of the most threatened species by anthropogenic and climate change impacts. Distribution and behavioural patterns can be difficult to determine for these wide-ranging, cryptic species that spend a limited amount of time at the surface, making direct observation difficult. Harbour porpoise (Phocoena phocoena phocoena, Linnaeus, 1758) is protected across European waters, listed under Annex II of the EU Habitats Directive, requiring Special Areas of Conservation (SAC) for their conservation. Despite its protected status, harbour porpoise are a relatively understudied species. It is therefore important to determine long-term habitat use patterns to ensure effective conservation is put in place. This research uses long-term passive acoustic monitoring (PAM) to increase our understanding of harbour porpoise habitat use in Irish waters.
Firstly, feeding buzzes and spatial-orientation echolocation clicks of harbour porpoise were differentiated within a 9-year PAM dataset from northwest Ireland (Chapter 2). The spatio-temporal distribution of foraging behaviour was investigated using Generalized Additive Models (GAMs), at multiple temporal scales. The research identified clear interannual and seasonal variation, with peak foraging buzzes detected in autumn, as well as highlighting a negative impact of construction related activities in the area. A new PAM monitoring network was also established in an SAC designated for harbour porpoise in southwest Ireland, over a 3-year period. GAMs were used to examine harbour porpoise occurrence and foraging behaviour in relation to intra-site differences in habitat use and environmental variables (Chapter 5). Harbour porpoise were detected year-round within the SAC, with seasonal trends in occurrence and foraging behaviour observed, with peak detections in the late autumn and winter reflecting similar trends from Broadhaven Bay (Chapter 2). Clear preferences in habitat use were identified, with porpoise occurrence and foraging varying across small spatial scales, as well as across diel, tidal, and lunar cycles. This research also noted an overall decline in acoustic detections across the monitoring period, reflecting wider population trends in Irish waters that bears further investigation.
An in-field comparison of a widely used PAM tool, the C-POD (Cetacean POrpoise Detector) with its recently developed successor the F-POD (Full waveform capture POD) was conducted, providing timely insights into the integration of this new equipment into acoustic monitoring programmes (Chapter 3). The F-POD recorded twice the amount of harbour porpoise detections compared to a co-deployed C-POD. GAMs highlighted similar patterns of harbour porpoise occurrence, however, in contrast to the F-POD, the C-POD failed to detect sufficient foraging rates to identify temporal trends in foraging behaviour. This work suggests that the switch to F-PODs will likely have minimal effect on our understanding of seasonal patterns of occurrence but may improve our understanding of foraging. Following on from this finding, an in-field playback experiment was conducted to determine the detection probability and effective detection radius/area (EDR/EDA) of three commonly used PAM devices, the C-POD, the F-POD, along with a continuous recording hydrophone (SoundTrap) (Chapter 4). The SoundTrap detected porpoise playbacks at the greatest distance, followed by the F-POD. The C-POD detection range was considerably less than the other two PAM devices. The type of harbour porpoise echolocation (spatial orientation clicks versus buzzes) was also found to influence the detection range, with clicks detected at a closer range across all devices. Understanding how this range of PAM devices compare provides valuable information to enable robust comparison of studies and inform appropriate planning of acoustic monitoring programmes.
Collectively, the research has significantly enhanced our knowledge of acoustic monitoring methodologies and identified key harbour porpoise habitat use patterns. The findings can inform more effective conservation management of harbour porpoise at a national and international level. Additionally, this research contributes valuable insights to inform the designation of protected areas to cover important feeding habitats, and ensure targeted protections are put in place in the future.
Description
Keywords
Harbour porpoise , Passive acoustic monitoring , Long-term monitoring , Cetaceans , Special area of conservation
Citation
Todd, N. R. E. 2023. A multi-method approach to understanding the ecology of harbour porpoise in Irish waters. PhD Thesis, University College Cork.