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Centre for Biodiversity & Ecology Research

Department of Biological Sciences, School of Science & Engineering

The University of Waikato, Hamilton, New Zealand

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 Invasive fish research

CBER's invasive fish research programme

CBER's invasive fish research programme focuses on investigations into the distribution and abundance of pest fish such as koi carp (Cyprinus carpio), goldfish (Carassius auratus), and brown bullhead catfish (Ameiurus nebulosus). We are also studying the ecological effects of pest fish and methods to improve capture efficiency and biosurveillance. Key equipment in this programme is our highly successful electrofishing boat. A 10 Mb PDF of a Powerpoint presentation is downloadable here.

Fish sampling in non-wadeable habitats The ability to catch pest fish in fresh water that is too deep for wading (1-3 m) is the key to determining the abundance, impacts, and biological effects of pest fish. Further, fish capture needs to be related to the area fished in order to establish density and biomass per unit area. Brendan Hicks and Dudley Bell have developed New Zealand's first successful electrofishing boat specifically to fish non-wadeable habitats. Since its launch in July 2003 we have used this boat in over 80 locations in the North Island of New Zealand to catch over 6,000 fish (total weight over 3.6 tonnes). We have developed multiple-pass boat electrofishing to give removal population estimates, and we use the on-board GPS unit to estimate the distance and area fished. Using this method, we have found that koi carp biomass in the Waikato region can reach 2,060 kg/ha.

Pest fish removal from selected habitats We have used CBER's electrofishing boat to remove koi carp from selected habitats of suitable size. Koi carp were removed from a pond on private land near Apata, Bay of Plenty, on 18 February 2004. We fished under contract to Environment Bay of Plenty (EBOP) and the Department of Conservation and the full cooperation of the landowner, catching 5 large adult koi carp in 3 hours. Since that time no koi have been seen in the pond, so it is possible that one intensive boat electrofishing session eradicated the koi carp from this habitat.

Invasive fish surveys Another major advantage of the electrofishing boat is way in which it allows us to fish 100s to 1000s of metres of habitat in a single day. Recently we were contracted by EBOP to fish the Waimapu Stream, Bay of Plenty, following a sighting of a "large, orange fish" by an observant whitebaiter. We have also surveyed the Waikato, Manawatu, Wanganui, and Mokau rivers, lakes Rotoiti and  McLaren in the Bay Plenty, and lakes in the lower Waikato basin. We have fished the Hikutaia Cut in the Waihou River system for Environment Waikato on 19 August 2003. This narrow lake is about 1 km long and 2-3 m deep; in it we caught koi carp, perch, goldfish, tench, and shortfin eels.

Fish from Hikutaia Cut, Waihou River system. Koi carp are to the left and top, European perch of a range of sizes are in the centre, goldfish occupy the right of the picture, and tench, including young of the year, are just above the ruler at the bottom. The left pectoral fin of many of the koi carp was missing or mutilated.