Use of shell shape variation as an assessment tool in the southernmost razor clam fishery

Morphological variation provides a method for phenotypic stock differentiation at inter- and intra-specific levels. Various methods are used for the assessment of fishery stocks in mollusks; one of them is geometric morphometrics. We analyzed morphological variation in razor clams at ten fishing grounds, five from the Argentinean North Patagonian gulfs and five from Chile, and evaluated the occurrence of phenotypic stocks between Argentinean and Chilean fisheries, using geometric morphometrics methods. The Argentinean harvesting of Ensis macha is emerging, and represents a way to diversify the shellfisheries in north Patagonia. Nevertheless, fishing and aquaculture play important roles for the Chilean economy. Various multivariate methods were applied to describe the differences among and between fishing grounds. We found significant differences in the average shell shape of individuals from either ocean, and these differences principally describe changes in the robustness of the shell. The average shell shapes differed among sites from the Pacific while those from the Atlantic Ocean did not show statistical differences. This study shows that geometric morphometric techniques are appropriate for the identification of phenotypic stocks in E. macha. Our results could be used for future resource management and to determine the origin of the product in razor clams from South America.