Observation of Tooth Scars on the Head of Male Sperm Whale, as an Indication of Intra-sexual Fightings

In order to examine the relation between intra-sexual fightings and sexual maturity, observations of tooth scars on the head of sperm whales (Physeter catodon) were made collected in South Pacific Oceans during 10 to 18 March 1979 on the Nisshin maru No. 3. Tooth scars on the head were observed on 48 males based on the following four relative stages; none, indistinct, distinct and heavy. Distinct tooth scars including "pallarel scar" which suggest intra-sexual fightings occurred among whales over 43 ft, and scars of most heavey stage were observed among whales over 46 ft in body length. Whales having relatively heavier scars were taken in solitary or a pair in either high latitudes (>40°S) or northern parts of females's range. Although no whales was directly taken from mixed school, three solitary large males taken around the mixed school had scars of most heavy stage. From the informations of body length, school size and catch position, most of these whales having relatively heavy scars were classified to large bachelor, these suggest intra-sexual fightings took place among large bachelors. The relation between tooth scar stage and testes weight were also examined. Mean weights of single testis (heavier) for males were 4.88 kg (combined both sides, 9.26kg) and 2.68kg (4.70kg) at scar stages of heavy and distinct, respectively. Comparing testis weights among the whales of same body length, whales with heavier scar tend to have heavier testis. In conclusion, it can be said that sexual maturity rate tend to increase with increasing of body length and with development of scar stages. This suggests that tooth scars indicate one of the evidences of sexual maturity.