Platypus fyke-netting methods: a review of recommended field protocols and options for assessing population abundance

Abstract

Fyke nets are the preferred type of equipment used for platypus (Ornithorhynchus anatinus) live-trapping surveys in shallow watercourses. However, numerous factors other than abundance may affect the frequency of platypus captures, including when, where and how nets are set, stream discharge and entry into nets by rakali (Hydromys chrysogaster), which create exit holes that are then also available to a platypus. A threefold difference in the mean monthly frequency of platypus captures in fyke nets is also evident across the year. To limit net evasion, it makes sense to reduce net visibility and minimise opportunities for animals to squeeze under, climb over or walk around nets. Time-lapse cameras can also be deployed at fyke-netting sites to estimate how many individuals evade capture. To protect platypus welfare and the welfare of non-target species held in fyke nets, it is important to ensure that captured animals have access to air, to check nets frequently throughout the time they are set and to release bycatch when first encountered. Fyke-netting studies typically generate sparse platypus population data, so care is needed when selecting and interpreting platypus abundance metrics generated through mark–recapture modelling or use of indices.