Exploring the use of otolith shape analysis to identify the stock spatial structure of dusky rockfish (Sebastes variabilis)

Abstract

Dusky rockfish (Sebastes variabilis) is a commercially valuable groundfish species in Alaska waters, with its highest abundance and fishery catch occurring in the Gulf of Alaska (GOA), and lesser abundance and catch occurring throughout the Aleutian Islands and southeastern Bering Sea. Despite its commercial importance, information regarding stock structure of dusky rockfish has been data-limited. In this study, otolith shape analysis was used to evaluate the stock structure of dusky rockfish across five geographical subareas exhibiting ecological differences in the GOA and Bering Sea and Aleutian Islands (BSAI), where dusky rockfish are managed as two separate stocks. A combination of size and shape indices, wavelet, and elliptic Fourier descriptors were examined from left and right-side otoliths collected from these regions (n = 522). Individual variation existed across subareas. Wavelet and elliptic Fourier descriptors indicated that mean otolith shapes were partitioned between the two management regions but also showed a high degree of overlap among subareas. Classification accuracies of otoliths to their subarea of origin through linear discriminant analysis (LDA) were variable (6.3–73.5 % and 15.4–65.8 % correctly classified for the elliptic Fourier and wavelet analyses, respectively). The highest classification rates were found between the western GOA and eastern Aleutian Islands, contributing to the observed differences between management regions and providing some support for current management paradigms. Dusky rockfish exhibited low to moderate overall classification rates (43.9–52.2 %), suggesting minimal stock structure within Alaska waters. This study highlights the utility of otolith shape analysis as a stock discrimination tool, and results will help refine further investigations and support fishery management in Alaska.