Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8616
Title: Genotype-based estimates of local abundance and effective population size for Hectors dolphins
Author: Rececca M. Hamner, Rochelle Constantine, Rob Mattlin, Robin S. Waples, C. Scott Baker
Publication Year: 2017
Journal: Biological Conservation
Keywords: abundance,mark recapture,effective popluation size,pHoto-identification,dolphin

Conservation and management decisions for wild populations are often based on demographic estimates of abundance (N ^), and less frequently, on genetic estimates of effective population size (N ^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 ^1+) to be 269 (95% CL=233-319, CV=0.12). This was similar to, but more precise than, N ^=230 (95% CL=130-407, CV=0.30) from the more traditional analysis using contemporaneously collected photo-identifications. The N ^e of the parental generation was 191 (95% CL=23-362), and the resulting N ^e/N ^1+ of 0.71 was in reasonable agreement with species of similar life history characteristics. Although N ^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 Ne. Our work demonstrates the breadth of management-relevant information (e.g., N, Ne, 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.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.
Describe the relationships between human activities and species recovery, rebuilding and sustainability.
Official Citation:

Hamner RH, R Constantine, R Mattlin, RS Waples, and CS Baker.  2017.  Genotype-based estimates of local abundance and effective population size for Hector’s dolphins.  Biological Conservation 211:150-160.