Journal Article

Relationship of Effective Size to Hatchery Supplementation and Habitat Connectivity in a Simulated Population of Rio Grande Silvery Minnow

Date: 2020/04/29

Author(s): Carson E.W., Osborne M.J., Turner T.F.

Publication: North American Journal of Fisheries Management, v. 40

URL: https://doi.org/10.1002/nafm.10453

DOI: 10.1002/nafm.10453

Abstract:

Simultaneous management actions often are used to improve the status of imperiled species, yet the effects of these actions can be difficult to determine. The endangered Rio Grande Silvery Minnow Hybognathus amarus is a short-lived fish with a dispersive life history and thus requires—but does not occupy—unfragmented habitat for recruitment and survival. We used Rio Grande Silvery Minnow as a model system for an individual-based simulation study to evaluate responses of genetic effective size to hatchery supplementation and fish passage in a managed population. Simulations were designed to test effects of fish passage on the relationship between estimates of inbreeding (N_eI) and variance (N_eV) effective sizes, which differ consistently (N_eI >> N_eV) in long-term genetic-monitoring data from hatchery-supplemented Rio Grande Silvery Minnow populations. Values of different effective population size measures should be identical in a demographically stable and connected (admixed) population but can differ substantially under nonequilibrium conditions. When a barrier prevented upstream dispersal, N_eI was associated negatively with rate of downstream dispersal and positively with supplementation rate, whereas N_eV was associated negatively with both. This mirrored observations from Rio Grande Silvery Minnow. Individual effects of dispersal and supplementation, however, were difficult to discern due to significant interaction between these factors. When connectivity was restored, N_eI and N_eV depended on supplementation rate, with positive association between N_eI and supplementation rate versus a negative association for N_eV and interaction terms, and effects of dispersal were nonsignificant. Although fish passage did not alter the difference between N_eI and N_eV, our study suggests that for Rio Grande Silvery Minnow, and potentially other intensively managed species in regulated rivers, fish passage may help to distinguish effects of management actions, such as supplementation, from effects of other demographic influences. More generally, explicit analytical consideration of differences in effective population size estimates can provide important details of genetic responses to management.