The broad distribution of Pacific sardine (Sardinops sagax)
along the Pacif ic coast of North America makes it difficult for fisheries managers to identify regional
stocks of this dominant small pelagic species. An investigation of morphometric characteristics of otoliths of
Pacific sardine across most of their range revealed regional differences in populations. In a survey of over 2000 otoliths, all ages (with an emphasis on age-1 recruits) were compared. Principal components analysis, multivariate analysis of variance, and a novel method derived from regression and residuals calculations, termed
perimeter-weight profiles (PWPs), revealed otolith similarities and differences. The results of the different
approaches to statistical comparisons did not always agree. Sardine otoliths from Mexican waters were generally
lighter and more lobate than those from U.S. and Canadian populations. Age-1 otoliths from northern California in 2006–07 tended to be heavier and smoother than those from other areas, including year-class cohorts from southern California. Comparisons of age-groups and year-classes of northern California otoliths with the use of the PWP models indicated signif icant trends in year-to-year patterns. In conjunction with other established indices of population
structure, otolith PWPs are a useful tool for identifying local and regional stocks of Pacific sardine and may help
distinguish populations of other fish species as well
