Comparing live-capture methods for nutria: single- versus multiple-capture cage traps

Herbivory and burrowing by nutria (Myocastor coypus) cause substantial ecological and economic damage. Trapping is a common, effective practice for reducing nutria damage; however, trapping approaches must continually be adapted to keep pace with evolving animal welfare and ethical issues and to more effectively target pest species of interest. Our objective was to evaluate the efficacy of 2 nonlethal trap types for nutria: single-capture (SCT) and multi-capture (MCT) cage traps. We established 3 MCTs and 3 SCTs at each of 7 sites on a 10,500-ha mixed-use island located 15 km northwest of Portland, Oregon, USA. We prebaited using carrots, apples, and sweet potatoes for ≥3 consecutive days before trapping. We checked traps daily, and an infrared motion camera was established near each MCT to document activity. We captured 26 nutria over 724 trap nights, and all captures occurred at 4 sites. Nutria captured by MCTs were larger (6.38 ± 1.68 [SD] kg, n = 10) than nutria captured by SCTs (4.21 ± 2.48 [SD] kg, n = 16; F1,25 = 5.51, P = 0.02). Camera surveillance showed multiple nutria present in an MCT on ≥2 occasions, although individuals <3.7 kg were able to escape. The MCTs were more expensive, larger, heavier, and more difficult to transport and deploy. However, MCTs were less likely to capture nontargets. Improvements to MCT door design would likely increase multiple catch opportunities and decrease escapes.