Criteria for aging the otoliths of Dissostichus eleginoides from South Georgia (Subarea 48.3) and an analysis of aging precision

A prerequisite for validation of an aging technique is a clear set of consistent aging criteria to test. Two sets of criteria ate presented for aging the otoliths of Dissostichus eleginoides, one (C1) developed from previous work on the same species; the other (C2) adapted from generalized criteria used to age high latitude fish from the north-west Pacific Ocean. Growth structures were found to occur at several scales and vary both within and between otoliths. Pairwise comparisons of repeat readings by one observer and readings by two observers showed considerable inconsistency in aging both within and between observers, reflecting the complexity of the otolith structure. Aging using criteria C1 was more precise than aging using C2. but tended to give higher age counts in younger fish than over the equivalent region in older fish. Both aging techniques indicated D. eleginoides to be a long-lived fish, but C2 indicated that captured fish may be mostly young, between 3-9 years old. The low precision for aging D. eleginoides indicates that techniques to maintain aging consistency without bias and within standardized limits of variation are likely to be important.