Evaluation of removal of the size effect using data scaling and elliptic Fourier descriptors in otolith shape analysis, exemplified by the discrimination of two yellow croaker stocks along the Chinese coast

摘要

Removal of the length effect in otolith shape analysis for stock identification using length scaling is an important issue;however,few studies have attempted to investigate the effectiveness or weakness of this methodology in application.The aim of this study was to evaluate whether commonly used size scaling methods and normalized elliptic Fourier descriptors (NEFDs) could effectively remove the size effect of fish in stock discrimination.To achieve this goal,length groups from two known geographical stocks of yellow croaker,Larimichthys polyactis,along the Chinese coast (five groups from the Changjiang River estuary of the East China Sea and three groups from the Bohai Sea) were subjected to otolith shape analysis.The results indicated that the variation of otolith shape caused by intra-stock fish length might exceed that due to inter-stock geographical separation,even when otolith shape variables are standardized with length scaling methods.This variation could easily result in misleading stock discrimination through otolith shape analysis.Therefore,conclusions about fish stock structure should be carefully drawn from otolith shape analysis because the observed discrimination may primarily be due to length effects,rather than differences among stocks.The application of multiple methods,such as otoliths shape analysis combined with elemental fingering,tagging or genetic analysis,is recommended for sock identification.