Using otolith morphometric analysis to improve species discrimination of blackspotted rockfish (Sebastes melanostictus) and rougheye rockfish (S. aleutianus)

Abstract

Blackspotted rockfish (Sebastes melanostictus) and rougheye rockfish (S. aleutianus) are sympatric species found in the North Pacific Ocean. However, these species were not identified as separate taxa until the mid-2000s, and they remain difficult to differentiate in the field. These species are managed as a single mixed stock despite the fact that the North Pacific Fisheries Management Council rates them as Tier 3 species, meaning that an individual assessment including historical data is required for each. In this study, we developed a technique that distinguishes these species on the basis of otolith morphology and age, allowing both old and new collections to be identified to the correct species. Tissue samples and otoliths were collected from 1847 specimens during survey seasons in 2009 and 2013. Tissue samples were identified genetically to species by using the Sma6 microsatellite locus. We used morphometrics, weight, and age from 859 otoliths to develop a logistic regression model that identified 97.3% of blackspotted rockfish and 86.2% of rougheye rockfish. Otolith shape analysis distinguishes rougheye rockfish and blackspotted rockfish and can allow for more focused management of these species.