A Young Basking Shark, Cetorhinus maximus, from Japan

Abstract

A young, female basking shark, Cetorhinus maximus (total length 2.6m) captured off the Pacific coast of Honshu, Japan, in early May 1977 was examined and estimated to be less than 6 months old, judging by the number of calcified rings in the vertebral centra. The elongate, hook-like snout with a ventral groove continuous with the palate is considered a characteristic juvenile feature of Cetorhinus, found only in very young specimens. It is thought that the snout structure is related to juvenile feeding, probably both in the mother's womb, if oophagy in fact occurs, and during the early, free-living stage, when the snout shape may increase the efficiency of water flow into the mouth. The likely rapid change from the juvenile snout condition to the adult type is probably produced by allometric growth of the rostral cartilages. The size and estimated age of the specimen conform well to a growth curve derived from Atlantic and Mediterranean basking sharks, indicating that no significant differences exist in age/length relationships of
Cetorhinus populations world-wid