Acoustic Survey

The ObSERVE Acoustic project was carried out by an international consortium, led by the Galway-Mayo Institute of Technology with partnership from the Marine Institute, JASCO Applied Sciences, SMRU Consulting and the Irish Whale & Dolphin Group.  Field studies began in May 2015 and continued until November 2016. The project was designed to provide independent scientific information on cetaceans based specifically on the underwater sounds that they produce.  This challenging project involved the targeted deployment and recovery of underwater listening devices that are designed to withstand extreme pressures in the deep ocean while picking up and recording a wide range of species, many of whose calls, whistles or echolocation clicks are identifiable but some of whose sounds and vocal behaviour are poorly known.

The area of interest for this specialised research consisted of much of Ireland's continental margin where the shallower continental shelf and slope meet the deep Atlantic (see Images below).  By combining fixed and moving surveillance methods known as Static Acoustic Monitoring [SAM] and towed Passive Acoustic Monitoring [PAM] this dynamic and physically complex region could be covered effectively across three seasons, and for a wide range of species from the smallest Harbour porpoise to the immense Blue whale

In total 1,657 days were monitored acoustically using eight SAM systems that were moored in waters 1.6-2km deep. Sixty percent of all listening days were covered simultaneously by two types of recording device (AMAR and C-POD) with JASCO's AMARs recording a total of nearly 3.8 million echolocation clicks and 375,000 tonal whistles made by cetaceans.

These fixed sound-based monitoring methods provided significant data on whale and dolphin presence and seasonal occurrence. Three mobile acoustic monitoring surveys were also completed in each year. This resulted in over 7,000km of offshore survey effort in the Atlantic (see survey lines image below).  Using an automated and manually validated detection program called PAMGuard, which received sound and detection information from the towed hydrophone system, more than 24 million candidate clicks were detected during these surveys.  This yielded a total of 1,322 cetacean encounters ('events') which were analysed further by the project team.

This offshore project provided vital insights into the frequency and seasonality of occurrence of several large whale species (for example Sperm whale, Fin whale and Blue whale) as well as the rarely seen deep-diving Sowerby's beaked whale and Cuvier's beaked whale and several other toothed cetacean species. 

Areas of steep seafloor topography along the continental slope, parts of which hold impressive and complex canyon features, emerged as important zones for these animals but deeper ocean basin waters were also significant for some whale species.  Overall, the importance of Ireland's Atlantic Margin for many whale and dolphin species, particularly the lesser known beaked whales and seasonal migrants, was highlighted.  The information gathered by this study greatly improves our knowledge of this offshore environment and, in combination with the ObSERVE Aerial project, will help to point the way forward for future management and conservation in the region.

For further information about the ObSERVE programme, please contact us at ObSERVE@dccae.gov.ie

 

Scientific Publications from the ​​ObSERVE Acoustic project:

First confirmed sighting of Sowerby's beaked whale (Mesoplodon bidens (Sowerby, 1804)) with calves in the Northeast Atlantic

Signals from the deep: Spatial and temporal acoustic occurrence of beaked whales off western Ireland