Investigation into the long-finned pilot whale (Globicephala melas) mass stranding event, Tolsta, na h-Eileanan Siar, July 2023

Section 4: Stranding group composition

The mass stranding event involved animals from all sex and age classes (six adult males, 30 adult females with six pregnant and nine recently post-partum, 11 juvenile males, seven juvenile females, and one newborn calf). "Juvenile" here refers to sexually immature animals, including those dependent on mothers and those nearing sexual maturity. An overview of the age, sex and reproductive status of the animals is given in Figure 3 and Tables 1 & 2.

The individuals exhibited a range of reproductive states. In total, 12 females were in a "resting" state, likely recovering from the energetic demands of gestation and lactation. Three non-pregnant lactating females may have been nursing a calf at the time of stranding. The six pregnant females showed varying stages of pregnancy ranging from a full-grown foetus at birth length (210cm) presenting as a suspected dystocia (difficult birth, typically caused by a large or awkwardly positioned foetus), to early-stage embryo (< 2cm long). Nine females showed signs of recent birth and were lactating. Three pregnant females were also lactating, suggesting recent conception and potential weaning of a previous calf. Age and kinship analysis is detailed in Figure 3 and Tables 1 & 2.