Aging discrepancy related to asymmetrical otolith growth for sablefish Anoplopoma fimbria in northern California.

Abstract

Otoliths (sagittae) were removed from a sample of 801 sablefish collected at sea from commercial otter trawl vessels in northern California from April through August 1984. This study presents a detailed examination of aging discrepancies between a) surface and b) broken and burnt (section) otolith aging methods, and considers possible mechanisms responsible for discrepancies. Sablefish age assignments based on the broken and burnt (section) aging method were higher than those based on surface aging for fish exceeding about 5-7 years section age. Beyond these ages, discrepancies increased with increasing section ages. The surface aging method assumes that there will be continual radial growth with increasing fish age, but otolith radius measurements showed that rate of radial growth dramatically decreased with increasing age and made surface aging unreliable for all but young fish. In contrast, otolith thickness measurements increased linearly with increasing section age and were highly correlated with section ages. When growth in length becomes slow, then surface ages are probably not accurate and discrepancies between surface and section ages dramatically increase with increasing section age.