An ageing methodology, growth parameters and estimates of mortality for hake (Merluccius australis) from around the South Island, New Zealand

Abstract

A method is described to determine the age of hake by counting zones in sectioned otoliths. The technique was validated to age 1 years from the progression of modes in length–frequency distributions, and for ages 2 years onwards by examining the state of otolith margins from fish sampled regularly over a one-year period. von Bertalanffy growth parameters are estimated for hake on the Campbell Plateau and Stewart–Snares shelf, on the Chatham Rise, and off the west coast of the South Island. Hake grow rapidly for about five years, but growth is slight after about 12 years. Female fish have a significantly faster rate of growth than males. A value forM of 0·20–0·25 is proposed. Differences in growth rates and population age distributions imply that there are at least two stocks of hake in New Zealand waters, with fish off the west coast of the South Island being distinct from those on the Campbell Plateau and Chatham Rise.