Growth and productivity of orange roughy (Hoplostethus atlanticus) on the north Chatham Rise

A new interpretation of orange roughy (Hoplostethus atlanticus) otoliths indicates that growth rates in this species are exceptionally slow. The otolith interpretations were supported by modal analysis of length‐frequency distributions of small juveniles. Parameters of the von Bertalanffy growth function were estimated to be L 8 = 42.50 cm standard length (SL), K = 0.059 year −1 and t 0 = ‐0.346 year. This gives an average SL after 1, 2, and 3 years of growth of only 3.1, 5.5, and 7.6 cm, respectively. The estimated average age of maturity is 20 years. It is further suggested that maximum age may exceed 50 years, the instantaneous rate of natural mortality is probably below 0.10, and spawning success may be highly variable. This combination of factors makes orange roughy susceptible to overfishing. The optimal instantaneous rate of fishing mortality is estimated to be less than 0.10.