Kōura or freshwater crayfish are an important component of aquatic food webs and are a traditionally important species to Māori in Aotearoa New Zealand. The tau kōura, a traditional Māori method for harvesting kōura, has been used for the past 20 years to successfully monitor kōura populations in the central North Island lakes. This method comprises bundles of bracken fern fronds or whakaweku (Pteridium esculentum) laid on the lakebed, which kōura colonise. Recently, this method has been adapted for use in lotic habitats and in the littoral zones of lakes.
The tau kōura has been shown to provide high catch rates of kōura, as well as a balanced sex ratio and a wide size class of kōura in lakes at depths ranging from 5 – 40 m, and so provides more representative data on population structure than alternative methods. In streams, kōura catches on whakaweku are comparable to those obtained by electrofishing but with lower labour input. In streams, their main advantage lies in their ability to sample deep-water areas such as pools and areas of soft substrates that cannot be sampled effectively using backpack electrofishing. Whakaweku, however, are less useful in lake littoral zones requiring a far longer soak time (~3 months) than baited traps, which are typically set overnight.
The tau kōura/whakaweku method has two essential requirements, the availability of suitable bracken fern and a minimum deployment time of 2 to 4 weeks, which may not be practical in studies where time is limited. It also means that whakaweku are more vulnerable to disturbance by storm events or tampering by the public. These requirements mean that the use of the tau kōura/whakaweku as a sampling method requires more careful planning than other sampling methods.