Biological basis for the management of New Zealand moki (Latridopsis ciliaris) and smoothound (Mustelus lenticulatus) fisheries

Abstract

The biology of moki (Latridopsis ciliaris) and smoothound (Mustelus lenticulatus) was studied, with special reference to the Kaikoura gill-net fishery. The fishery developed in 1970, and catches of moki and smoothound reached peaks in 1974-75. Catch per gill-net vessel has declined markedly for both species since 1974. Gill-nets are set predominantly in 50 m to 100 m of water down the continental slope.

Moki are only abundant during short, regular "runs" at all major moki ports (Kaikoura, Wellington, Napier and Gisborne) but the timing of runs varies with the locality. Moki have developing gonads during the May-June Kaikoura run, ripe gonads in the August Gisborne run, and spent gonads in the October-November Kaikoura run. An annual spawning migration of a single moki stock along the east coast of New Zealand from Kaikoura to Gisborne (where the only known spawning ground is located) and back to Kaikoura is hypothesised to explain observed differences in gonad maturity state and the timing of runs at different localities. Moki mature at about 40 cm fork length and an age of four to five years, Most moki caught at Kaikoura are over ten years old, and fish as old as thirty years have been recorded. Preliminary Bertalanffy growth estimates were: K = 0.16; L = 80 cm; tₒ = -0.37.

Smoothound enter shallow water all around the New Zealand coast in spring and summer for parturition, copulation and ovulation of a new set of eggs. Young are born at a length of about 30 cm following a ten month gestation period. Females probably produce young every year. Fecundity increases with size, but approximately 7% of ovulated eggs are infertile. Males mature at 75 - 90 cm long, and females mature at 90 – 100 cm, Maximum observed lengths were 114 cm for males and 137 cm for females. Bertalanffy growth curves extrapolated from embryo growth rates gave K= 0.30 for females and K = 0.37 for males.