Expedition report: Photo-identification and surveys of cetaceans in the central group of the Azores islands (March - April 2025)

ABSTRACT In 2025 Biosphere Expeditions concluded its 19th year of cetacean photo-identification and distribution studies in the Azores. The expedition was based in Horta on the island of Faial and work was conducted around the three islands of Faial, Pico and São Jorge. The expedition ran from 18 March to 18 April 2025. 129 sightings of eleven different species of cetacean and three loggerhead turtles were recorded during the expedition period. Baleen whale photo-identification: Blue Whale: The expedition recorded twenty-three blue whales in thirty- five encounters, five individuals were seen on two different days. One individual had been seen on the 27th February and the 4th March, prior to the expedition. Photos of individuals were shared with catalogues in Spain, Iceland and Canada. Two blue whales matched to Pico/Faial, March 2024 and another individual to Pico/Faial, 2011 & 2018 and to São Miguel in 2023. The whale seen since February had previously been seen in Faial/Pico in 2018. Other individual blue whales, seen on previous expeditions, were sighted by other companies in Faial/Pico in 2025. No international long-range matches were found. Matches were made by Richard Sears of Mingan Island Cetacean Society. Fin whale: Five fin whales were recorded in five encounters. Identification photos were shared with catalogues in Spain, Iceland & Canada. No matches were found. Humpback whale: Four humpback whales were recorded over 4 encounters during the expedition. Three individuals showed the fluke. No matches were found in either the North Atlantic Humpback Whale Catalogue or the online platform Happywhale. Since 2004, the expedition has contributed 32 ID photos, helping to elucidate movements of the eastern Atlantic humpback whales, about which little is known. Minke whale: A single minke whale was seen during the expedition. Summary: 2025 was an incredible year for blue whale sightings during the expedition, with multiple animals seen on multiple days. There were further blue, fin, and humpback whales seen after the expedition, but the majority of blue whales in 2025 were seen during the expedition. Sperm whale photo-identification: Sperm whales were seen on a few days during the expedition. Sperm whale photo-identification, ongoing since 1987 in the Azores, continued. Nineteen identifiable individuals were photographed from fifty encounters, including three animals seen in previous years in the Azores, sixteen new individuals and two flukes that were unidentifiable. There were no long-range matches. Non-fluking males or social groups meant fewer fluke ID images in 2025. Dolphins: Dolphin: Photo-identification, which began in 1987, also continued. Two of our main dolphin photo- identification target species were encountered: Four groups of Risso’s dolphin and four groups of bottlenose dolphin were recorded. Both the bottlenose and Risso’s dolphin groups had some known individuals from resident groups. In addition we also saw two less common photo-identification targets: orcas and false killer whales were seen on the first day at sea. Common dolphin were also observed, although they are not target species for photo-identification. Beaked Whales: One group of three Sowerby’s beaked whales was seen during the expedition. This was the first confirmed sighting of Sowerby’s beaked whales since the expedition started in 2004. Europhlukes & Happywhale: Sperm whale fluke shape extractions were made from the photos taken during the expedition using the Europhlukes program “Phlex” and then matched with “Match” to flukes of sperm whales sighted in previous years as well as other areas of the Atlantic. No matches were found to any other regions. Happywhale was used for the first attempt at matching both sperm whales and humpback whales. POPA: Data for the Department of Oceanography and Fisheries (DOP) of the University of the Azores, for the Tuna Boat Observer programme, POPA, was successfully collected for a 19th year. The expedition vessel “Physeter” is the only non-fishing vessel in the programme. Information was collected for random cetacean sightings along transects, as well as designated turtle and bird count surveys and marine debris sightings. Turtles: Loggerhead turtle data have been collected and animals tagged in the Azores since 1988 for a joint venture between the University of Florida and the University of the Azores. During this expedition three loggerhead turtles were seen, but none were caught and tagged due to weather conditions, other research priorities or the turtles diving.