Boat electrofishing survey of the Waimapu and Kopurererua streams, Bay of Plenty, Waitara River, and a pond at Mokoia, Taranaki

Abstract

We conducted boat electrofishing surveys at four sites to establish the presence of, and to remove, koi carp (Cyprinus carpio). We fished the lower Waimapu Stream, Bay of Plenty, on 15 April and 14 June 2005, and the adjacent Kopurererua Stream on 15 June 2005. We caught and removed two large koi carp ( a 7.9 kg male and a 6.9 kg female) from the Waimapu Stream in 15 April, but saw no other koi carp in 3.2-km reaches of both streams on 14-15 June. We did, however, catch a wide diversity of native fish species, including common smelt, shortfin and longfin eels, yelloweye mullet, brown and rainbow trout, giant bullies, and black flounder. We also caught a lamprey macrophthalmia in the Waimapu Stream. No koi carp were found in a 2.4-km tidal reach of the Waitara River, northern Taranaki, on 8 June 2005, but we did catch a sparse native fish assemblage of adult inanga, shortfin eels, a few common smelt, black flounder, yelloweye mullet, and a 200-mm giant bully. We caught and killed 16 large koi carp (total weight 58.5 kg) from a pond on private farmland near Mokoia, southern Taranaki, on 9 June 2005. This pond had a perimeter of 215 m, a surface area of 951 m², and maximum depth of 2.0 m. These fish were removed by depletion fishing in 7 circuits of the pond. We caught 9, 3, 1, 1, 1, 1, and 0 carp in successive circuits. The Zippin method of population estimation (±95% confidence interval) suggests that there were 16±1 koi carp in the pond, so it is possible that we eradicated all of the koi. All the carp were the same age and no juveniles were found, so it appears that the carp had not breed successfully in this pond.