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 there is still relatively little 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 as well. Herein, 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 dataset) for individuals stranded between 1979 and 2023. Organ size was measured in 12 individuals. Most white-beaked dolphins (85%) stranded on the coastline of the outer Danish waters, with January, May, and June as the most common months for stranding. Males made up 41% of the dolphins in this study, 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, nor were seasonal, sexual, or geographical differences found in blubber thickness. The intestines had a median length of 20.5 m (18.30 to 23.90 m) 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’ biometric measurements.