Abstract

This study, attempts to discriminate stocks by using otolith morphometric and shape. From 1996 to 1999, 235 Gag were sampled from commercial and artisanal fishery catches taken on the Campeche Bank, at southern Gulf of Mexico. Both otoliths (sagittae) were removed through the gill arch, alcohol cleaned, stored dry in small paper bags, and weighed (weighted average; 0.1 mg). Each left otolith was consistently oriented at a 45° position (sulcus side down, rostrum upwards to the right) and digitally photographed using a stereomicroscope at 3.2 X an 4 X equipped with a video camera. Otolith morphometric measurements were obtained using Image-Proâ Plus V6 software and included: area, rectangularity, area (polygon), maximum and minimum diameter, perimeter, ellipse, and roundness. Otolith shape was determined through Age & Shape software using 11 wavelets scales (WLT) each one with 512 radii measurements per otolith. Gag standard length ranged from 22.7 to 100.0 cm and total weight 245.3 to 20,450.0 g. Ages ranged from 4 to 13 years. Prior to statistical analysis, all eleven WLT scales were standardized by dividing each amplitude by the mean radial otolith length. A PCA showed that WLT2, WLT4, WLT5, WLT6 and WLT7 and rectangularity, roundness, perimeter and ellipse accounted for 99% of the variability in the data and were used in further analyses. MDS analyses and ANOSIM tests were carried out to test if there were significant differences of PCA-WLT and PCA-morphometrics between Northern, Eastern, and Western fishing grounds in the Campeche Bank. Analyses found no discernible groups using Euclidean distance or Gower similarity coefficient, and no statistically significant differences between fishing grounds.