Catch-at-age of yellowtail kingfish 2010
Yellowtail kingfish are an important component of the recreational fishery in northern New Zealand and a valuable by-catch for commercial fishers. Recreational fishers that regularly targeted kingfish where asked to measure all their catch and to retain heads from fish that were kept. The project aimed to describe the length, sex, and age composition of the recreational catch of kingfish for the 2010–11 fishing year to help determine the status of the kingfish stock in the KIN I management area.
Funding: Ministry for Primary Industries
Researchers: Blue Water Marine Research and NIWA
Southern yellowtail kingfish (Seriola lalandi lalandi) have been recorded from latitude 29° to 46° S (Kermadec Islands to Foveaux Strait), but are predominantly found around the North Island and also occur at the top of the South Island in summer. Juveniles are often associated with rafts of floating debris or seaweed. Adult kingfish are large predatory fish that can exceed one and a half metres in length. They usually occur in schools ranging from a few fish to well over one hundred individuals. Adult kingfish tend to occupy a semi-pelagic existence and occur mainly in open coastal waters, preferring areas adjacent to rocky outcrops, reefs and pinnacles, particularly around off-shore islands. However, kingfish are not restricted to these habitats and are sometimes caught or observed in open sandy bottom areas and within shallow enclosed bays and harbours.
The harvest surveys of amateur fishers estimate an annual catch of yellowtail kingfish of several hundred tonnes.  Reported commercial catch in KIN 1 peaked at 378 t in 1992–93 and declined steadily to 49 t in 2003–04 and has remained 50 to 60 t since then. Commercial methods do not appear to catch the full size range of yellowtail kingfish, with a bias toward smaller fish.
A total of 2091 kingfish were measured in this survey. Of these, 1287 (62%) were released, 711 (34%) without being tagged. Recreational fishers collected 460 kingfish heads from East Northland, Hauraki Gulf and the Bay of Plenty collected between February and November in 2010. Otoliths were removed and prepared as thin sections allowing annual rings to be counted.
Young kingfish grew rapidly and started to recruit to the fishery (the minimum legal size of 75 cm) as three year olds, and were fully recruited at 4 or 5 years. Few teenage fish where taken in the catch, especially from East Northland. The oldest and largest fish sampled in East Northland was a 156 cm fish (41.6 kg) caught in Bream Bay aged at 22 years.
Chapman and Robson estimates of total mortality (Z) differ between the two sub-regions; with fewer older fish in East Northland implying a higher level of fishing mortality than for the Bay of Plenty.