Morphological and genetic variation among shortnose sturgeon Acipenser brevirostrum from adjacent and distant rivers

Shortnose sturgeon, Acipenser brevirostrum, is a small, endangered species which occurs in 19 estuary systems along the east coast of North America. T hese populations are considered as separate entities by the U.S. National M arine Fisheries Service although evidence of morphologic or genetic differe ntiation among populations has not been documented. The purpose of this stu dy was to compare morphological and genetic attributes among shortnose stur geon collected From the Kennebec and Androscoggin Rivers, Maine, and the Hu dson River, New York. Six morphometric and five meristic characteristics we re quantified. Multivariate and univariate analyses of covariance and varia nce were used to assess differences among populations. Our analyses provide d evidence for distinct populations in the Androscoggin and Kennebec Rivers , but character differentiation was greater between fish from these two loc ations and the Hudson River. Analysis of morphometric characters indicated significant differences in fish shape among the three rivers, with Hudson R iver sturgeon differing from the Maine rivers for the characters of head le ngth, snout length, and mouth width. Significant differences were observed for meristic characters, but pairwise comparisons did not reflect a clear p attern of variability. Sequencing of a portion of the mitochondrial DNA con trol region revealed 15 haplotypes among 73 total specimens from the three rivers. Shortnose sturgeon from the Kennebec and Androscoggin Rivers were d ifferent from each other (p = 0.0260); both differed significantly (p < 0.0 001) from the Hudson River collection. Gene flow was estimated at approxima tely 7 female migrants per generation between the two Maine populations and about 1 per generation between each of the Maine populations and the Hudso n River population. Such strong stock structuring among presumably recently established post-Pleistocene (< 10,000 yr) populations suggests that this species occurs in highly discrete units, Morphological and genetic variatio n observed in this study combined with current knowledge of life history at tributes of shortnose sturgeon indicate that conservative management decisi ons are necessary until the patterns and extent of differentiation among po pulations species-wide can be investigated further.