Contemporary and historical effective population sizes of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is an anadromous fish of considerable conservation concern, following its long history of overfishing and exposure to a variety of other anthropogenic stressors. Though reaching a large size, population abundances (Nc) of Atlantic sturgeon are not easily surveyed using traditional fishery methods because of their relative scarcity and their many age classes, often exhibiting extensive and differential movements that render them not readily amenable to traditional sampling efforts. A metric of their vulnerability to inbreeding and a possible alternative to Nc for abundance monitoring is effective population size (Ne). We surveyed 14 Atlantic sturgeon populations across their range using a suite of DNA microsatellite markers. Contemporary levels of Ne ranged from 1 in the St. Marys River, Florida-Georgia, to 156 in the Hudson River, New York. Historical Ne estimates averaged about 11.5xhigher than contemporary estimates, with a high of 927 for the Kennebec River population. Because of a mix of life history characteristics that make traditional Ne estimates based on imperfectly mixed year classes of juveniles questionable, we propose and provide results ofa new, more robust and diagnostic approach based on sequential cohorts, termed Ne Max. Although contemporary Ne values obtained were at levels that might be considered troublesome, we suggest that the unique life history factors of this species may render it more resistant than other taxa to inbreeding effects. Because of the many differences among populations in size, age, and sex ratio and in harvest histories, we do not believe that a reliable extrapolation factor between Ne and Nc is yet possible. However, ongoing monitoring of Ne and Nc in populations might be sensitive to population changes and could form the basis of determining a relationship between Ne and Nc.