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Boat electrofishing survey of the Awaiti and Bancrofts canals (Tee Head Canal), Piako River system

This purpose of this survey of Awaiti and Bancrofts canals was to establish the presence of fish in the canals and to determine their relative density and biomass by boat electrofishing. These canals drain the Kopuatai Peat Dome and adjacent farmland into Tee Head Canal, which is part of the Piako River system in the Waikato Region. Awaiti Canal had patches of the emergent macrophyte Eurasian reed sweet grass (Glyceria maxima) and floating common duckweed (Lemna minor). Bancrofts Canal had dense beds of reed sweet grass and water pepper (Persicaria hydropiper, syn. Polygonum hydropiper) that extended into the water along most of its margin to the extent that the bank was not visible. The water of both canals was tannin-stained, but Bancrofts Canal had heavier staining than Awaiti Canal. We boat electrofished five sites in Awaiti Canal and five sites in Bancrofts Canal for 10 mins each on 21 February 2018. Water temperature was 24.3°C in Awaiti Canal and 23.1°C in Bancrofts Canal. In Awaiti Canal, ambient electrical conductivity was 313.5 µS cm⁻¹, specific conductivity was 317.6 µS cm⁻¹, and black disc distance was 0.18 m. In Bancrofts Canal, ambient conductivity was 174.3 µS cm⁻¹, and specific conductivity was 180.8 µS cm⁻¹. We caught 31 fish in total, 28 in Awaiti Canal and 3 in Bancrofts Canal. Species included shortfin eels (Anguilla australis), inanga (Galaxias maculatus), goldfish (Carassius auratus), brown bullhead catfish (Ameiurus nebulosus) and gambusia (Gambusia affinis). Two inanga at site 4 (Awaiti Canal) were retrieved dead on capture, as was the one eel retrieved in Bancrofts Canal. Fish densities were very low, up to a maximum of 1.02 fish 100 m-2 for all species combined at site 3 in Awaiti Canal. Only gambusia were found alive in Bancrofts Canal. Biomass per site and areal biomass were similarly very low, and this was partly attributable to the small size of individuals, which suggested that, with the exception of gambusia, they were young, newly recruited fish. Awaiti Canal had a low diversity of small fish species that are generally tolerant of poor water quality. This fish diversity is particularly low considering the close proximity of the sites to the coast (about 30 km from the Firth of Thames). The most diverse fish communities in New Zealand are found close to the coast. Typical mean eel densities in the Waikato River assessed by boat electrofishing were 0.7-1.3 eels 100 m⁻² compared to the mean of 0.12 fish 100 m⁻² (range of 0-0.29 eels 100 m⁻² ) at the five sites Awaiti Canal. Bancroft Canal had only gambusia, and the one shortfin eel found dead could have drifted in or died in the canal, probably as result of low DO concentrations.
Type of thesis
Hicks, B. J., & Bell, D. G. (2018). Boat electrofishing survey of the Awaiti and Bancrofts canals (Tee Head Canal), Piako River system. ERI report 110. Client report prepared for Waikato Regional Council. Hamilton, New Zealand: Environmental Research Institute, University of Waikato.
Environmental Research Institute, University of Waikato