Age determination, validation, and growth of blue cod Parapercis colias, in Foveaux Strait, New Zealand

Abstract

Blue cod (Parapercis colias) is an important inshore commercial and recreational fish species in the southern islands of New Zealand, and estimates of their growth rate, age at maturity, and longevity are required for fisheries management. This study provides validation and comparisons of ageing methodologies for blue cod in Foveaux Strait, Southland. Sectioned otoliths showed a consistent banding pattern, and counts of these had good consistency between readers. Scales, broken and burnt, and whole otoliths gave lower band counts than equivalent sectioned otoliths counts. Blue cod otoliths were small, and otolith weights and lengths showed no relationship with sectioned otolith band counts. Marginal increment analysis provided a partial validation of ages estimated from sectioned otoliths, and oxytetracycline marking completed the validation for blue cod over 300 mm total length. Fin spines also showed promise as an excellent and non‐lethal ageing tissue. Blue cod growth in Foveaux Strait was then described and compared to previous studies, which are likely to have underestimated ages because of the use of broken and burnt and whole otoliths.