Spatial variations in beak structure to identify potentially geographic populations of Dosidicus gigas in the Eastern Pacific Ocean

We explored an approach to using morphological variables of suqid body and beaks to identify different geographic populations for Dosidicus gigas. We tested this approach using a total of seventeen morphological variables of body and beaks measured for 1490 squids sampled outside the exclusive economic zone (EEZ) waters off Ecuador, Peru and Chile. Linear regression analysis showed significant and positive relationships between beak morphometric variables and mantle lengths. All measured beak variables were significantly different among the three regions (p < 0.001), with samples from the areas off Chile and Ecuador having the largest and smallest beaks, respectively. The morphometrics of squid beaks showed a significant sexual dimorphism and were useful for sex determination (p < 0.001), although considerable overlaps were found in the scatter-plots. Hard structure (i.e., beaks) variables were shown more effective than soft body in population discrimination, although a stepwise discriminant analysis (SDA) suggested that both the body and beak morphometric variables are useful for the geographic population discrimination. We found that the standardized beak and body variables are more effective in separating D. gigas potentially geographic populations than the original variables.