Using Tooth Rakes to Monitor Population and Sex Differences in Aggressive Behaviour in Bottlenose Dolphins (Tursiops truncatus)

This study investigated intraspecific tooth rake scarring, an established indicator of received aggression by conspecifics, on bottlenose dolphins (Tursiops
truncatus) to gain knowledge of aggressive interactions. The differences in tooth rake scarring between male and female dolphins on the east coast of Scotland were examined, and overall levels of scarring were compared with dolphins on the west coast of Scotland (Sound of Barra and Hebrides). Photographs were examined for evidence of tooth rake scarring using four different methods. East
coast males displayed significantly higher scarring percentages (i.e., body area covered by tooth rake scarring), numbers of dorsal fin rake directions (i.e.,
whether tooth rake scars were vertical, horizontal, diagonal, or curved), and nick percentage (i.e., amount of the dorsal fin missing due to nicks) than females. Differences also existed between the three areas, with bottlenose dolphins around the Sound of Barra showing significantly lower levels of dorsal
fin rake directions than those on the east coast or Hebrides. Observed sex differences are likely the result of intrasexual conflict between males over
access to females. However, other factors such as sex- or age-specific behaviours or sexual coercion of females may also be involved. Such information
could potentially be used to differentiate between the sexes. The differences in dorsal fin scarring between these populations suggests differences in aggressive
interactions, possibly indicating differences in social structure. The lower scarring levels seen in the Sound of Barra group may support the suggestion
that bottlenose dolphins on the west coast belong to two communities. However, this variability in conspecific aggression may also be the result of different
social behaviours, age or sex ratios, habitat, resources, or individual behavioural differences.