Identification of Illex coindetii , I . illecebrosus and I . argentinus (Cephalopoda: Ommastrephidae) throughout the Atlantic Ocean; by body and beak characters

Abstract

Shortfinned squid species of the genus Illex support commercial fisheries throughout the Atlantic Ocean and Mediterranean Sea. Previous identification of interspecific and intraspecific populations by morphological and size-at-maturity studies have not provided conclusive results. We analysed morphometric body and beak variables (24 characters) in three species of the genus (I. coindetii, I. illecebrosus and I. argentinus), using a geographic and seasonal series of 33 populations for 1,500 specimens of I. coindetii, I. illecebrosus and I. argentinus. Residuals of the regression between each morphometric body and beak variable and mantle length were used as input in a stepwise discriminant analysis. Species discrimination by body and hectocotylus characters required at least eight variables and resulted in high correct-classification percentages for I. coindetii and I. argentinus (75% and 90%, respectively), whereas the best identification resulted from beak characters (83% correctly classified

Stock identification of neon flying squid (<em>Ommastrephes bartramii</em>) in the North Pacific Ocean on the basis of beak and statolith morphology

“…Many studies have focused on interspecies identification, with relatively high classification rates using beaks (Martínez et al 2002, Pineda et al 2002). The total correct classification rate was nearly 50% for both statoliths and beaks, but increased to about 70% for the combination of both hard parts.…”

“…Thus, measurements based on the soft parts of squid are challenging and frequently contain errors, and an alternative structure should be used to separate stocks on the basis of body morphology. However, these measurements are fairly reliable if the approach is correct, as in the studies of Loliginidae by Pierce et al (1994) and of Ommastrephidae by Martínez et al (2002).…”

“…It has been proved that hard structures with a stable form can perform better than soft tissues (mantle, arm, tentacle, etc.) in squid population division (Martínez et al 2002). Some new methods (landmarks and outline study) have also revealed that hard structures give good results in identity analysis (Dommergues 2000, Neige and Dommergues 2002, Lombarte et al 2006, Neige 2006, Crespi-Abril et al 2010.…”

“…Multivariate analyses of morphometric data have been used in some cephalopods at intraspecies (Martínez et al 2002) and interspecies (Wolff 1984) levels for the evaluation of taxonomic and geographic variations. Stocks inhabiting different environments can impact their growth patterns, including the shapes of statolith and beak.…”

“…Stocks inhabiting different environments can impact their growth patterns, including the shapes of statolith and beak. It is common that the separation of stocks is only based on one material and then compared with the results obtained from different materials (Martínez et al 2002), and the approach of integrating two materials in the stock separation is rarely used. In this study we integrated the morphological variables of statolith and beaks to compare their differences between stocks and between the sexes and to establish a discriminant function for two seasonal cohorts in the North Pacific Ocean.…”