Download FAR 2025/30 Age estimation and catch-at-age of southern bluefin tuna (Thunnus maccoyii) in the New Zealand surface longline fishery, 2022–2024

This report describes research conducted in 2022, 2023, and 2024 to determine the age of southern bluefin tuna (Thunnus maccoyii; STN) caught in New Zealand’s surface longline (SLL) fishery. Ages were assessed using counts of opaque and translucent zones in STN otoliths (‘ear bones’). Otoliths used this this study were collected from fish heads supplied by Licensed Fish Receivers (LFRs), collected by observers onboard SLL vessels, or from sampling of the recreational fishery in a related Fisheries New Zealand project. A total of 150, 156, and 163 STN were aged in 2022, 2023, 2024, respectively. Assigned ages ranged from 2–26 years old, with most aged fish around 4–12 years old. An age-length key was constructed applied to the lengths of STN provided by LFRs to estimate the age structure of the SLL catch in each year. The information generated by this study will be used for assessments and fisheries management advice.