Download FAR 2024/44 Age composition of northern gemfish in 2012, 2014, and 2022

Middleton, D.A.J.; Robertson, S.; Horn, P.; Langley, A.D. (2024). Age composition of northern gemfish in 2012, 2014, and 2022. New Zealand Fisheries Assessment Report 2024/44. 34 p.

Information on the age composition of fish catches is desirable for undertaking fully quantitative stock assessments.

Monitoring, using catch-per-unit-effort (CPUE), has demonstrated that abundance of the northern stock of gemfish increased substantially since the mid 2010s.

This has led to interest in undertaking more detailed stock assessment modelling. To support this modelling, catch-at-age data were compiled for the 2012, 2014, and 2022 fishing years.

Otoliths (fish ear bones, the structures used for assessing fish age) were available from sampling of landings from the northern gemfish target trawl fishery in 2012 and 2014. New sampling of this fishery was carried out in 2022 by Fisheries New Zealand observers.

Samples from these three years were aged, with care taken to ensure that the techniques and results were comparable with those used to provide earlier age data for gemfish.

In 2012 and 2014, nine- to ten-year-old females and eight- to nine-year-old males were the most common age classes in the catch.

Younger male and female gemfish dominated the catch in 2022. Few of the age classes sampled in 2022 had been sampled in previous years.