Stable isotopic comparison in otoliths of juvenile sablefish ( Anoplopoma fimbria) from waters off the Washington and Oregon coast

Genetic methods have been extensively used in the examination of fish population composition and structure. However, it is generally not easy to determine the stock structure of marine fish using the genetic markers, particularly given the large population size and wide spread distribution of long-lived fish. As an alternative, sagittal otoliths of juvenile sablefish ( Anoplopoma fimbria) along the Washington and Oregon coast were collected and analysed for stable oxygen and carbon isotope ratios. δ 18 O values of the otolith nuclei ranged from −1.3 to +0.1‰ VPDB, whereas δ 13 C of the same otoliths ranged from −8.7 to −6.2‰ VPDB. In contrast with the lower isotopic composition in early life, δ 18 O and δ 13 C values of sablefish otoliths at adult stage were levelled at about 2.0‰ VPDB and −1.0‰ VPDB, respectively. From north to south three different spawning stocks or subpopulations were recognized, with a gradual decrease in otolith δ 13 C and trophic level changes in sablefish’s diet. Therefore, stable isotopic records of otoliths may be a potential supplement for genetic markers when studying the stock structure of marine fish.