Biometrics of stranded white-beaked dolphins (Lagenorhynchus albirostris) in Danish waters

White-beaked dolphins (Lagenorhynchus albirostris) are among the most common toothed whales in the North Sea, but still relatively little is known about their general biology and their biometrics. The white-beaked dolphins are known to breed in the outer Danish waters and have recently been documented as breeding in inner Danish waters too. Here we present the biometrics (stranding location (n=128), stranding month (n=129), sex (n=103), reproductive status (n=103), length (n=102), external body dimensions (n=90) and blubber thickness (n=57; 22 with complete data set)) for individuals stranded between 1979 and 2023. Organ size was measured in 12 individuals. Most white-beaked dolphins (85%) were stranded on the coastline of the outer Danish waters, and with January, May and June as the most common months for stranding. Males made up 41%, of which 73% were immature, while only 36% of the stranded females were immature. Apart from the curve measures around the genital slit, no differences in the relative lengths of external measurements were found between males and females. No seasonal, sexual or geographical differences were found in blubber thickness. The intestines had a median length of 20.5 meter (18.30-23.90 meters) from the duodenum to the pelvic part of the rectum. Measurements of beak to belly button, beak to dorsal fin and tail width were highly correlated (R2<65%, p<0.0001). These data contribute to increased knowledge of white-beaked dolphins' biometrical measures.