Boat electrofishing survey of the Kaituna River and Bell Road oxbow

The Department of Conservation (DOC) and Bay of Plenty Regional Council contracted the University of Waikato to conduct a boat electrofishing survey of the Kaituna River and Bell Road oxbow. This survey was in response to sightings of large orange fish in the oxbow by members of the public and the consequent concern that these fish might be koi carp (Cyprinus carpio). We also recorded species of native fish to determine their relative density and biomass in the oxbow and the adjacent Kaituna River. The 10 sites fished in the Kaituna River and Bell Road oxbow (latitude 37.743780°S, longitude 176.359509°W) are located about 5 km northeast of Te Puke township and about 5.5 km upstream from the sea. Both the oxbow and the main river channel are tidal at this point. The oxbow had a diverse macrophyte assemblage of hornwort (Ceratophyllum demersum), the oxygen weed Egeria densa, floating sudds of reed sweetgrass (Glyceria maxima), and water pepper (Persicaria hydropiper), with scattered plants of curly-leaved pondweed (Potamogeton crispus). There were also small amounts of parrot’s feather (Myriophyllum aquaticum), floating water fern (Azolla rubra), duckweed (Lemna minor), watercress (Nasturtium officinale), and native pondweed (Potamogeton ochreatus). The main river channel had fringing beds of the oxygen weeds Lagarosiphon major and Elodea canadensis below the low water mark. All sites where fished on 8 October 2014; surface water temperature was 14.7°C in the oxbow at the start of fishing at 1030 h, ambient conductivity was 187.0 μS cm⁻¹, and specific conductivity was 232.8 μS cm⁻¹. Black disc distance was 0.98 m. In the main river channel at 1440 h ambient conductivity was 106.6 μS cm⁻¹, and specific conductivity was 136.7 μS cm⁻¹. We fished 1,953 m in length and an area of 7,812 m2 from a total of ten sites. We caught a total of 127 fish, with shortfin eel the most abundant species. Longfin eel comprised 14.0 kg of the total fish biomass caught of 26.4 kg. The 24 goldfish caught in the oxbow comprised 3.3 kg of biomass. Common, giant, and redfin bullies were about equally abundant. Yelloweye mullet were caught only in the main channel of the river. Shrimp were caught in varying numbers at all sites v, the mid-water shot in the oxbow. As the purpose of this fishing was to establish the identity of large orange fish seen in the Bell Road oxbow, the finding of goldfish was significant. From the size and colour ranges and abundance of the goldfish caught in the oxbow it is highly likely that any orange fish seen in the oxbow were large orange goldfish and not koi carp