Advances in morphometric identification of fishery stocks

Geographic variation in morphometry has been used todiscriminate local forms of fish for over a century. The historical development of stock identificationmethods has paralleled the advancement of morphometrictechniques. The earliest analyses of morphometricvariables for stock identification were univariatecomparisons, but were soon followed by bivariateanalyses of relative growth to detect ontogeneticchanges and geographic variation among fishstocks. As the field of multivariatemorphometrics flourished, a suite of multivariatemethods was applied to quantify variation in growthand form among stocks. More recent advances have beenfacilitated by image processing techniques, morecomprehensive and precise data collection, moreefficient quantification of shape, and new analyticaltools. Many benchmark case studies and critiquesoffer guidelines for sampling morphometrics andinterpreting multivariate analyses for exploratorystock identification, stock discrimination, and stockdelineation. As examples of morphometric stockidentification based on life history differences,allometric patterns of crustacean secondary sexcharacters have been used to detect geographicvariation in size at maturity, and morphometriccorrelates to smoltification have been used todiscriminate salmon from different rivers. Morphometric analysis provides a powerful complementto genetic and environmental stock identificationapproaches. The challenge for the future ofmorphometric stock identification is to develop aconsensus on biological interpretations of geometricanalyses, similar to the conventional interpretationsof size and shape from traditional multivariatemorphometrics.