Validation of the formation and appearance of annual marks in the otolithsof yellowtail (Trachurus novaezelandiae) and blue mackerel (Scomber australasicus) in New South Wales

Yellowtail (Trachurus novaezelandiae) and blue mackerel (Scomber australasi cus) were captured off the coast of New South Wales, marked with oxytetracy cline, and kept in captivity for 1 year. The fish were periodically sampled to validate the use of their otoliths for age estimation. Opaque marks wer e formed during the year in the otoliths of yellowtail apparently aged 0 to 7 years and in apparently 1-year-old blue mackerel. These marks were forme d in winter for both species, but did not become visible until early summer in some fish. There was an association between the growth rate of the otol ith and the detection of opaque marks. Within an age class, fish with the f astest growing otoliths tended to have their most recently formed opaque ma rks visible earliest. These relationships between growth rate and the proba bility of correctly assigning an age class have important implications for ageing fish.