Age and growth estimates for New Zealand hapuku, Polyprion oxygeneios

Polyprion oxygeneios (family Polyprionidae) is fished commercially and recreationally in the southern Indian and Pacific Oceans. Estimates of growth rate, age at maturity and recruitment, and longevity are required for fishery management. We used thin otolith sections to age P. oxygeneios from New Zealand, where it is known as hapuku. Growth bands were difficult to count, leading to low counting precision and, for some age groups, to a small between- and within-reader ageing bias. These problems, however, had little effect on the shape of growth curves fitted to length-at-age data. An oxytetracycline injection experiment supported our hypothesis of annual deposition of an opaque-hyaline band pair, but further validation is required. Independently derived von Bertalanffy growth curves (from length-frequency data) and growth-rate estimates (from tag-recapture data) for young hapuku agreed well with estimates from length-at-age data. Juvenile hapuku are pelagic and most switch to a demersal habitat at around 50 cm total length and at an estimated age of 3-4 years. They probably recruit to commercial trawl catches at about the same age. Female hapuku appear to grow slightly faster than males. Both sexes mature at about 10-13 years. The longevity of hapuku is uncertain, but some individuals probably live longer than 60 years.