Evaluating otter reintroduction outcomes using genetic spatial capture-recapture modified for dendritic networks.

Area of Science:

• Wildlife ecology and conservation genetics
• Population dynamics and spatial ecology
• Non-invasive genetic monitoring techniques

Background:

• Reintroduction success hinges on monitoring demographics and genetics, yet challenging species ecology and landscapes impede accurate assessments.
• Hierarchical dendritic networks, like river systems, constrain animal movements, potentially violating assumptions of standard demographic estimation methods.
• North American river otters (Lontra canadensis) are a key species for aquatic ecosystem health and reintroduction efforts.

Purpose of the Study:

• To demonstrate the applicability of the spatial capture-recapture (SCR) network distance function for estimating population size and density.
• To evaluate the genetic outcomes of a small founder group (n=33) in a recently reintroduced river otter population.
• To assess the long-term viability and genetic health of the reintroduced river otter population in the Upper Rio Grande.

Main Methods:

• Utilized genetic detection data from fecal samples collected at latrines for spatial capture-recapture (SCR) analysis.
• Applied the SCR network distance function to account for movement constraints within the dendritic river network.
• Assessed genetic diversity, effective population size, and genetic divergence from the source population 8-10 years post-reintroduction.

Main Results:

• Estimated population density of 0.23-0.28 otter/km, with an estimated population size of 83-104 otters in 359 km of river.
• Observed average annual population growth of 1.12-1.15/year, which was ≥40% lower than most reintroduced river otter populations.
• Detected strong evidence of a founder effect, including 13-21% genetic diversity loss, 84-87% effective population size decline, and rapid genetic divergence (FST = 0.06/generation).

Conclusions:

• The SCR network distance approach is effective for demogenetic assessments in dendritic habitats, applicable to various mustelid species.
• The small founder group resulted in significant genetic diversity loss and reduced population growth, raising concerns for long-term viability.
• Genetic restoration via translocation of additional otters may be necessary to mitigate deleterious genetic effects in this isolated population.