Trace elements in the otoliths of New Zealand blue grenadier (Macruronus novaezelandiae) as an aid to stock discrimination

Abstract

Blue grenadier, Macruronus novaezelandiae, or hoki as it is known in New Zealand, spawns at two distinct localities off New Zealand. Earlier research on morphometrics and on age and growth suggested that these spawning localities are used by two discrete stocks; however, the research was not conclusive. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) was used to analyse trace elements in otoliths from adult blue grenadier collected at the two spawning sites. Before analysis, portions of otoliths formed during juvenile and adult life were isolated and these segments were analysed separately. With a cross-validation procedure (jackknife), it was possible to classify correctly 100% of the samples in relation to age (juvenile v. adult). On the basis of the jackknifed discriminant functions, classifications of blue grenadier in relation to sex or capture locality were not significantly different from random. The results are not definitive in determining stock structure of New Zealand blue grenadier but do provide insight into the application of otolith trace element chemistry in studies of stock structure.