Up to 380 sperm whales are living in deep waters off the Irish coast, a newly published study has found.
This makes sperm whales “one of the most abundant great whale species” in these waters, expert Dr Simon Berrow says.
Sperm whales are known for their distinctive echolocation “clicks” which can be heard over many tens of kilometres, and this allows them to be counted.
A survey team from Galway-Mayo Institute of Technology (GMIT) and the Scottish Sea Mammal Research Unit (SMRU) Consulting spent 45 days at sea in harsh weather conditions to conduct the population count.
Deploying towed hydrophone from RV Celtic Voyager Photo: Simon Berrow
“With high sea states and towering swell, the study relied purely on being able to detect the distinctive powerful click trains of sperm whales using a streamlined towed hydrophone or underwater microphone array,” Dr Berrow said.
The results were published recently in the Journal of Cetacean Research and Management, following detailed sea surveys dating back to 2015.
Dr Berrow, the principal investigator on the study, noted that the deep-diving tendency of sperm whales makes them difficult to observe at sea – they can spend nearly an hour in depths below 300m.
Only 11 individuals were sighted during 388 hours of effort, he said, but 391 acoustic detections were recorded.
Sperm whales off Ireland’s west coast Photo: Irish Maritime Squadron
“Each whale was pinpointed by comparing the exact time that each click arrived at each hydrophone in the array and then triangulating bearings from sequential clicks over extended encounters,” he said.
The whales seemed to prefer seabed areas that sloped to the northwest, including the Erris and Rockall Basins.
There was also a dense concentration of sperm whales in the South Brona Basin canyon system near 350km west of Co Kerry
The surveys were carried out from the Marine Institute’s RV Celtic Voyager and the yacht Song of the Whale, operated by Marine Conservation Research Ltd.
The study was part of the ObSERVE-Acoustic project funded by the Department of Communications, Climate Action and the Environment and the National Parks and Wildlife Service.
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