DOC contracted University of Waikato researchers to survey the invasive fish in three ponds on private land in the Kauri Point catchment (area about 250 ha) in the Bay of Plenty, North Island, New Zealand, and to remove as many koi carp as possible. We designated these artificially created ponds, in a sequence from upstream to downstream, as Pond A (~6,500 m2 in area), Pond B (~1,800 m2), and Pond C (~1,750m2) at NZMS 260 sheet U13 2771890E 6405535S (longitude 175.960073°E, latitude 37.513733°S). Before fish removal, the water in Pond A was extremely turbid (Figure 1). If you have Google Earth, click here to go to the site location. This opens best with Mozilla Firefox browser.
Figure 1. Pond A before carp removal
On 21 and 22 April 2008, we spent about 7 hours fishing with the University of Waikato's electrofishing boat (Figure 2). We caught a total of 327 fish comprising of 307 koi carp (Cyprinus carpio, 137.5 kg of biomass), 1 goldfish (Carassius auratus), and 19 koi-goldfish hybrids were captured and removed from the three ponds by a combination of boat electric fishing (307 fish) and mist netting (20 fish). The majority of these fish (299 koi, 1 goldfish, 19 koi-goldfish hybrids) were removed from Pond A. Mosquitofish (Gambusia affinis) and eels (Anguilla sp.) were also in the ponds, but their abundance was not estimated. Inanga were found only the most downstream pond (Pond C).
Figure 2. Electrofishing boat and crew fishing on Pond A. The boat crew, left to right, is David Klee, Jeroen Brijs, and boat Driver Dudley Bell.
Figure 3. Sizes of koi carp ranged from 60 to 520 mm, suggesting that carp were breeding successfully in Pond A.
Removal electrofishing gave a population estimate of 358 ± 66 koi carp and hybrids, of which we removed 299 by electrofishing and 20 by mist netting, suggesting that about 139 carp remain in the ponds. Carp biomass was estimated as 145 ± 44 kg, or 223 ± 68 kg/ha. As we removed 122 kg of carp, the carp biomass remaining is about 23 kg, or 35 kg/ha. The four size classes of the carp (60 to 520 mm; Figure 3) suggest that they have been breeding successfully in Pond A.
Hicks, B.J., J. Brijs, J. Heaphy, and D.G. Bell. 2008. The use of boat electrofishing for koi carp (Cyprinus carpio) control in the Kauri Point catchment. CBER Contract Report No. 69. Centre for Biodiversity and Ecology Research, Department of Biological Sciences, School of Science and Engineering, The University of Waikato, Hamilton.