Mark-recapture is a common technique for estimating animal population size and density. Obtaining unbiased estimates relies on an understanding of basic population dynamics (immigration, emigration, birth, death) and whether marking individuals affects their likelihood of recapture (survival, behavior). Salamanders are ubiquitous, diverse, and abundant in forests in the eastern US, and it is well understood that they play important ecological roles. The same is increasingly clear for larval salamanders in streams, and recent studies have used mark-recapture to estimate larval stream salamander densities. A leading alternative to marking with traditional tissue removal techniques is the injection of a visible implant elastomer (VIE). However, using VIE with small salamander larvae made us question whether the brightly colored marks that are visible to researchers would bias our density estimates if marks make salamanders more visible to predators. We conducted lab and field experiments to test the effects of VIE marking on larval two-lined salamander (Eurycea bislineata) survival with fish and crayfish. We also conducted a field experiment to measure whether VIE marking affects prey capture by salamander larvae.
Results/Conclusions
Contrary to our expectations, survival in the presence of fish was higher for marked than unmarked salamanders in both laboratory and field experiments. Crayfish did not affect salamander survival. Prey capture by marked salamanders was lower than unmarked, suggesting the higher survival experienced by marked salamanders is a result of lower movement and foraging rates. Although VIE is a common and useful technique for marking small amphibians, it does affect survival and behavior. Such effects will bias estimates of density, and contrary to our expectations, may result in underestimates of population density.