Female, juvenile, and calf sperm whale Physeter macrocephalus (Linnaeus 1758) records from Ireland.

ABSTRACT

Sperm whales spatially segregate by sex and social behavior as they mature. In the North Atlantic, male whales move to higher latitudes as far as Svalbard at 80° N, while females and young whales typically remain around lower latitudes below 40-45° N. The Azores, Madeira, and the Canary Islands constitute important nursery grounds for female and young sperm whales. Irish waters represent a midpoint for this species' spatial segregation in the Northeast Atlantic, where the species occurs along the submarine canyon systems to the west of the country. Historically, just male whales were thought to be found in this region between 51 and 55° N, but one adult female was caught by commercial whalers in 1910, and a 5.49 m calf was found stranded in 1916. Between 1995 and 2023, 10 female sperm whales have been stranded around the coast of Ireland. Eight of these whales have been stranded since 2013, and there has been at least one stranding per year between 2019 and 2023. Four of these strandings have occurred in Donegal in the northwest of Ireland, indicating the presence of female whales along the continental shelf off this region. Two females were stranded within a day of each other and were found in similar states of decomposition in February 2022, indicating that they may have been part of the same group rather than being lone vagrant individuals. Sperm whale calves and juveniles were also sighted in Irish waters in 2001, 2004, and 2010 in the Rockall Trough, along the Porcupine Bank and Goban Spur, where between 1 and 3 individuals were observed on four occasions while one calf live stranded in 2004. These records indicate a historical presence of female and young sperm whales in this region but that an apparent increase in occurrence has taken place over the past decade.