The Department of Conservation (DOC) and Bay of Plenty Regional Council contracted the University of Waikato to conduct a boat electrofishing survey of the Awatapu Lagoon, the old Rangitaiki River channel and the lower Tarawera River. This survey was in response to sightings of large orange fish at these sites by members of the public and the consequent concern that these fish might be koi carp (Cyprinus carpio; Pete Livingstone, DOC, Whakatane). We also recorded species of native fish to determine their relative density and biomass.
We fished the Awatapu Lagoon in October 2005 and December 2014, and we fished the old Rangitaiki River channel and the lower Tarawera River in December 2014. In the Awatapu Lagoon on 31 October 2005, we caught 260 fish, comprising 170 goldfish weighing a total of 27.5 kg, 88 shortfin eels (Anguilla australis), and two brown trout. In addition, common smelt (Retropinna retropinna), inanga (Galaxias maculatus) and gambusia (Gambusia affinis) were abundant, though their numbers were not quantitatively determined. The two adult brown trout we caught measured 450 and 460 mm fork length (FL), giving calculated weights of approximately 1.21 and 1.29 kg. Mean goldfish density was 1.70 fish 100 m⁻², with individuals ranging in size from 40 to 277 mm (FL) (mean FL 178 mm ± 42 mm standard deviation, SD). Mean weight of 162 g (± 97 g SD), and mean goldfish areal biomass was 1.70 g m⁻². Shortfin eel density was estimated as 1.87 fish 100 m⁻² in East Lagoon, but biomass was not estimated for shortfin eels. Eels were seen in West Lagoon but not caught. No koi carp or other invasive fish species were found.
In December 2014, we caught 271 fish comprising 12 species (two introduced, and 10 native). Common bullies (Gobiomorphus cotidianus) and shortfin eels were the most numerous species. In the Awatapu Lagoon, we caught 102 common bullies, 64 goldfish and 22 shortfin eels. In the lower Tarawera River, we caught parore (Girella tricuspidata), a stargazer (Leptoscopus macropygus), and yelloweye mullet (Aldrichetta forsteri). Site T4 in the Tarawera River had the greatest species richness (7 species). We verified that the large orange cyprinids that were seen in the old Rangitaiki River channel were large goldfish and not koi carp.
As the main purpose of this fishing was to establish the identity of large orange fish seen in and round the lower Tarawera and the Awatapu Lagoon, the occurrence of goldfish was significant. From the size and colour ranges and abundance of the goldfish caught it is highly likely that any orange fish seen were large orange goldfish and not koi carp. However, before this fishing it was quite reasonable to conclude that large orange fish might be koi carp. This is similar to the Kaituna River, where goldfish were found but there were no koi carp. The high diversity of native fish species in the lower Tarawera River is predictable from known fish distribution patterns, where the most diverse fish communities are found close to the coast. The occurrence of parore is unusual in freshwater fishing, as these are generally considered to be a marine species, but do stray into estuaries. One giant bully was found in this survey, and these are quite common in the lower reaches of large river systems. Yelloweye mullet are also common in Bay of Plenty fresh waters close to the sea. Stargazers are a relatively unusual catch, but we have found these previously in Bay of Plenty rivers and in the lower Manawatu River.
