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Morphological, Meristic, And Genetic Analysis Of Stock Structure In Juvenile Atlantic Cod (Gadus Morhua) From The Newfoundland Shelf

Pierre Pepin, Steven M. Carr

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We examined joint patterns of variation among 11 morphological variables, vertebral counts, and DNA sequence variation in the mitochondrial cytochrome b gene among juvenile (0-group) Atlantic cod (Gadus morhua) from the northeast Newfoundland shelf and the Grand Banks. Canonical discriminant analysis shows that the group centroids of fish on and off the Grand Banks are significantly different and that fish from the most southerly region (3O) have a significantly smaller mean vertebral count than fish from the more northerly regions (3K, 3L); however, there is substantial overlap of individuals, and reclassification of fish into their region of origin is successful in less than 50% of cases. Analysis of the distribution of 10 DNA sequence genotypes indicates substantial homogeneity of genotypes within localities and little or no genetic subdivision among regions. The pattern of genetic differentiation is consistent with a model of recent origin of most genetic variation following a bottleneck in population numbers. The combination of morphological, meristic, and genetic analysis of juvenile cod in NAFO Divisions 3K, 3L, and 3O does not support the hypothesis of stock separation among these areas. In particular, our data do not support the use of vertebral counts to define stock separation during early life history.