713 Kusabs & Quinn—Monitoring of ko - ura by traditional Ma - ori harvesting method New Zealand Journal of Marine and Freshwater Research, 2009, Vol. 43: 713–722 0028–8330/09/4303–0713 © The Royal Society of New Zealand 2009 M08031; Online publication date 25 June 2009 Received 26 June 2008; accepted 27 November 2008 Use of a traditional Ma - ori harvesting method, the tau ko - ura, for monitoring ko - ura (freshwater crayish, Paranephrops planifrons) in Lake Rotoiti, North Island, New Zealand IaN a. KuSabS Te arawa Lakes Trust P.O. box 128 Rotorua, New Zealand email: ian@kusabs.co.nz JOhN M. QuINN National Institute of Water and atmospheric Research Limited P.O. box 11 115 hamilton, New Zealand Abstract Sampling of kōura (freshwater crayish Paranephrops planifrons) to assess population abundance and structure in lakes is often dificult or impractical because of the absence of representative methods. The tau kōura is a traditional Māori method used to catch kōura in central North Island lakes by placing whakaweku (bundles of bracken fern Pteridium esculentum) on the lake bed that kōura then colonise. It has advantages as a monitoring tool over conventional methods, such as baited traps and dive surveys, as it samples all kōura size classes, can be used in turbid waters and at a wide range of depths, and does not require expensive equipment or specialised expertise (e.g., SCUBA). We demonstrate its use to monitor kōura populations in Lake Rotoiti (mean depth 32 m), North Island, New Zealand. application of the method allowed differences in population size structure to be distinguished between a shallow and a moderate depth site within Lake Rotoiti and to discern seasonal breeding patterns. Keywords Te Arawa; Ngati Tūwharetoa; Rotorua lakes; population size structure; abundance; catch- per-unit-effort; sex ratio; egg-bearing INTRODUCTION Large populations of kōura (freshwater crayish, Paranephrops planifrons) have been reported in several central North Island lakes in New Zealand, e.g., Rotoiti, Rotoma, Okataina, Tarawera, and Taupō (Devcich 1979). Kōura are an important traditional food source for Māori (Hiroa 1921). Furthermore, Māori throughout New Zealand are reasserting the principle of kaitiakitanga—the sustainable protection of resources (Tipa & Teirney 2006). Kaitiakitanga ensures conservation, protection and maintenance of resources through responsible actions, behaviour, conduct, and practices. Therefore it is important for iwi (Māori tribe) and hapū (Māori sub-tribe) organisations to be active participants in the resource consent monitoring process, i.e., kaitiakitanga, in which Māori monitor their own mahinga kai (traditional food resources and places where they are gathered) as part of active participation in the sustainable management of lake ecosystems. There is considerable anecdotal evidence of declines in lake populations of kōura since European settlement (Hiroa 1921). A number of environmental factors may be responsible for this decline, including introductions of exotic ish which prey upon kōura (McDowall 1987; Barnes & Hicks 2003), exotic plant species which likely hinder movement and accumulate large amounts of organic detritus (I. Kusabs pers. obs.), as well as reduced concentrations of dissolved oxygen in the bottom waters of lakes owing to eutrophication (Vincent et al. 1984; hamilton et al. 2005). although these changes have been documented individually, their collective inluence may have had a considerable impact on kōura populations. The ecology of stream-dwelling kōura is relatively well studied in New Zealand (Hopkins 1967a,b; Hicks & McCaughan 1997; Rabeni et al. 1997; Parkyn 2000; Parkyn et al. 2001, 2002a,b), but little is known about kōura populations in New Zealand lakes. The only detailed study of lake-dwelling kōura was carried out by Devcich (1979), who focused on the ecology of kōura in Lake Rotoiti (North Island).