CBER's invasive fish research programme

Pest fish Survey of Awatapu Lagoon

Awatapu Lagoon (NZMG 2858634 E 6352274 N) is part of a park reserve of the Whakatane District Council and is located within the precincts of Whakatane township. It was formed when an ox-bow of the Whakatane River was isolated as part of a major scheme by the Bay of Plenty Catchment Commission in 1970. Plantings have been carried out over the years, and these have enhanced the reserve's vegetation. It has an approximate area of 7.7 ha and a maximum depth of 2.5 m. Macrophyte species in the lagoon include hornwort, parrots feather and the emergent species raupo.

Figure 1. Awatapu Lagoon in Whakatane township boat electrofished on 31 October 2005.

The lagoon was surveyed on 31 October 2005 by Waikato University staff using the University's electrofishing boat. After fishing for nearly 2 hours covering a distance of nearly 3000 m, a total of 2 brown trout, 88 shortfin eels and 170 goldfish were captured. In addition, numerous smelt, inanga and gambusia were also sited but not recovered. The two brown trout measured 450 and 460 mm (Fork length) giving calculated weights of approximately 1.21 and 1.29 kg. The goldfish ranged in size from 40 to 277 mm (FL) (mean 178 mm ± 42 mm SD) with a mean weight of 162 g (± 97 g SD). This gave a tentative goldfish density of 22 fish/ha with a biomass estimate of 3.93 kg/ha. Shortfin eel density was calculated at 11.4 fish/ha, biomass estimates for shortfin eels could not be estimated.

Figure 2. Large orange-coloured wild goldfish (277 mm fork length) with small bronze-coloured goldfish from the Awatapu Lagoon, Whakatane River, 31 October 2005.

Awatapu Lagoon therefore appears to have good stocks of native species including shortfin eels, inanga and smelt and relatively few invasive fish species. Further plantings and restoration should facilitate habitat improvement and encourage the development of other native fish populations.