Genotype-based estimates of local abundance and effective population size for Hector's dolphins

Conservation and management decisions for wild populations are often based on demographic estimates of abundance ((N) over cap), and less frequently, on genetic estimates of effective population size ((N) over cap (e)). We used genotype based methods to estimate both parameters from the same set of biopsy samples, while also providing information on the geographic closure of a local population of Hector's dolphins in Cloudy Bay, New Zealand. The assumption of closure in Cloudy Bay was supported by the lack of genetic differentiation between the two survey years and the absence of any genetically detectable migrants. Using recapture analysis based on genotype identifications, we estimated the abundance of individuals age 1(+) ((N) over cap (1+)) to be 269 (95% CL = 233 - 319, CV = 0.12). This was similar to, but more precise than, (N) over cap = 230 (95% CL = 130 - 407, CV = 0.30) from the more traditional analysis using contemporaneously collected photo-identifications. The (N) over cap (e) of the parental generation was 191 (95% CL = 23 - 362), and the resulting ($) over cap (e)/($) over cap (1+) of 0.71 was in reasonable agreement with species of similar life history characteristics. Although (N) over cap (e) was below the recommended threshold (500, recently increased to >= 1000) thought to be necessary to preserve long-term evolutionary potential in perpetuity, genetic connectivity with neighboring populations on a generational time scale is likely to mitigate the negative effects of low local N-e. Our work demonstrates the breadth of management-relevant information (e.g., N, N-e, sex ratio, genetic diversity, and connectivity to neighboring populations) that can be obtained from a genotype-based analysis, and how conservation implications can change when demographic and genetic population size are considered along with connectivity.