Advances in morphometric identification of fishery stocks

Geographic variation in morphometry has been used to discriminate local forms of fish for over a century. The historical development of stock identification methods has paralleled the advancement of morphometric techniques. The earliest analyses of morphometric variables for stock identification were univariate comparisons, but were soon followed by bivariate analyses of relative growth to detect ontogenetic changes and geographic variation among fish stocks. As the field of multivariate morphometrics flourished, a suite of multivariate methods was applied to quantify variation in growth and form among stocks. More recent advances have been facilitated by image processing techniques, more comprehensive and precise data collection, more efficient quantification of shape, and new analytical tools. Many benchmark case studies and critiques offer guidelines for sampling morphometrics and interpreting multivariate analyses for exploratory stock identification, stock discrimination, and stock delineation. As examples of morphometric stock identification based on life history differences, allometric patterns of crustacean secondary sex characters have been used to detect geographic variation in size at maturity, and morphometric correlates to smoltification have been used to discriminate salmon from different rivers. Morphometric analysis provides a powerful complement to genetic and environmental stock identification approaches. The challenge for the future of morphometric stock identification is to develop a consensus on biological interpretations of geometric analyses, similar to the conventional interpretations of size and shape from traditional multivariate morphometrics.