Age, growth and maturity of a New Zealand endemic shark (Mustelus lenticulatus) estimated from vertebral bands

Abstract

Rig (Mustelus lenticulatus) specimens were aged by counting growth bands in whole vertebrae that were illuminated laterally with fibre-optic lights. Bands were counted by two readers who used information on the diameter of the vertebrae of new-born young and 1-year-old juveniles to identify the inner bands. The greatest estimated age was 12.1 years for a female of 137 cm total length, but few rig were more than 8 years old. For west coast South Island (WCSI) rig, there was no significant difference in growth rates of males and females. After pooling both sexes, there was no significant difference in growth rates between WCSI and east coast South Island (ECSI) rig. The combined WCSI and ECSI von Bertalanffy growth curve was L_t = 147.2 (1 – e ^{−0.119[t + 2.35]}). This curve agreed well with growth curves derived from length–frequency data, but validation of the ageing technique is still required. WCSI males mature at ~85 cm and 5–6 years, and females at ~100 cm and 7–8 years. ECSI rig probably mature at similar lengths and ages. Tagged rig have been recaptured after nearly 14 years at liberty. Longevity probably exceeds 15 years, and may exceed 20 years.