geographic variations of jumbo squid (dosidicus gigas) based on gladius morphology

The jumbo flying squid (dosidicus gigas) is widely distributed in the eastern pacific ocean and its population structure is complex. morphometric analysis of hard structures of cephalopods is frequently employed to explore the geographic variation within discreet population units. in this study, 8 morphometric characteristics of the gladius, or pen, were measured and compared from 562 jumbo squid specimens collected off peru, the costa rica dome, and from the equatorial central eastern pacific. the growth rate of the gladius was evaluated by comparing it with the ages determined from statoliths. results showed significant differences in gladii morphology between sexes and geographic populations. stepwise discriminant analysis indicated that gladius morphometric characteristics were suitable discriminatory variables with an overall correct classification rate of 78.6% for distinguishing different populations. higher daily growth rates were found in the proostracum than in the conus, possibly because of the different biological functions of these anatomical parts. these results support our general hypothesis that gladius morphology provides an alternative way to distinguish potential geographic populations of d. gigas and it adds new information regarding the gladius of the ommastrephidae.