Sampling efficiency, bias and shyness in funnel trapping aquatic newts

A lightweight, collapsible funnel trap designed for crayfish was furnished with a smaller mesh and then used to study adult breeding populations of five species of newts in five ponds in France. Observations were made in spring, at the peak of breeding activity, over an 11-year period. Annual experiments involved on average 7.7 traps and 5.3 overnight sampling sessions at 2.0 day intervals. In 95 out of 171 experiments (56%) the probability for an individual to go undetected was <1%. A trend was observed for catchability to increase with body size (Lissotriton < Ichthyosaura < Triturus). The two Triturus species were frequently exhaustively sampled in a single overnight session. In spite of their smaller size, L. helveticus males were more readily captured than females, presumably reflecting breeding associated locomotor activity. The numbers captured decreased over time suggesting ‘trap shyness’ to operate. We noted some predation by diving beetles (family Dytiscidae) affecting L. helveticus males in particular.