OTOLITH SHAPE ANALYSIS AND ITS APPLICATION IN FISH STOCK DISCRIMINATION:A CASE STUDY

This study was to discriminate four tapertail anchovy Coilia nasus stocks in the coastal waters of the Bohai Sea and the Yangtze River Estuary of China by means of otolith shape analysis including size variables and shape variables. Removing fish length effects on otolith shape analysis and stock identification by both ANCOVA adjustment and allometric growth adjustment were also critically assessed. Results showed that these two adjustment methods achieved an overall classification success (discriminant function analysis) of 50.3% (39.5%—90.0%) and 56.5% (34.0%—65.1%) for the four geographical stocks, respectively, where no significant difference is observed. Otolith morphometrics differed significantly among the three fish length groups of the tapertail anchovy in the Yangtze River Estuary, suggesting that otolith shapes could change markedly as fish grows. ANCOVA adjustment and allometric growth adjustment on fish length produced an overall classification success of 94.8% and 98.8%, respectively, for the three fish length groups in this region. In general, otolith shape variables (e.g., rectangularity, roundness, fractal dimension and the Fourier coefficients) could contribute more to the success of stock identification than size variables (e.g., perimeter, mean diameter, weight and area), whereas a combination of both kinds of variables could obviously improve the ability of otolith shape analysis to effectively dis- criminate stocks.