INFERRING SPAWNING MIGRATIONS OF ORANGE ROUGHY (HOPLOSTETHUS-ATLANTICUS) FROM SPAWNING OGIVES

Orange roughy (Hoplostethus atlanticus) occurs throughout New Zealand waters at depths between 700 and 1500 m. Most spawning occurs in a few localized aggregations in winter and it appears that fish migrate sub stantial distances (hundreds of kilometres) to and from these aggregat ions. However, there is no direct evidence of migration. Indirect evid ence of migration of females is presented in the form of trends in L-5 0, the mid point of the spawning ogive (i.e. the length at which 50% o f mature females are spawners). Data from 21 research surveys carried out between March and August over an eleven-year period show consisten t geographical trends in L-50 on the east coast and the Chatham Rise. L-50 was consistently low (28-32 cm) near major spawning grounds and i ncreased to high values (>34 cm) far from these grounds. These trends increase the knowledge of orange roughy spawning migrations in two imp ortant fishing areas.