Dudding Lake’s carp mystery
A council wanting to release foreign grass carp into a lake to control weeds says it has no idea how the fish species managed to already get in the water.
Dudding Lake in Rangitı¯kei was subject to a public health warning in December after high levels of blue-green algae were found there.
Scientists said the lake was at risk of ‘‘flipping’’ – becoming dominated by algae instead of the native plants that grow on the lake bed.
Rangitı¯kei District Council wants to release grass carp into the lake to eat non-native weeds, creating space for native species and ka¯kahi, or freshwater mussels. It believed doing so would improve the lake’s health, although leading freshwater scientist Dr Mike Joy said it would lead to carp creating nutrient for the non-native weeds to continue growing.
The council has applied to the Department of Conservation to release the carp, but it turns out the fish is already in the lake.
The issue came up at Horizons Regional Council’s environment committee meeting yesterday, when councillors asked officers what had happened.
Horizons freshwater partnerships manager Logan Brown said one carp had been found in the lake during fish monitoring.
The monitoring initially found smaller species expected to be in the lake, but nets came up with holes in them, he said.
That led to larger nets being used, which found the grass carp.
It was being kept in a freezer, he said. It was not clear if there were more carp in the lake, or how long the found carp had been in there, he said.
In letters provided by the Rangitı¯kei council to Stuff, the Department of Conservation’s Manawatu¯ operations manager Moana Smith-dunlop asked for an explanation.
‘‘Fish can’t walk.’’
In reply, Rangitı¯kei council chief executive Ross Mcneil said his council did not know how the carp got in there or who could be responsible.
The council still wanted its application to release grass carp into the lake to go ahead regardless, believing the fish had a role to play in improving the lake’s condition, he said.