Pest fish proving a hard catch for researcher

Efforts to get rid of pest fish in Waikato lakes are proving difficult as researchers struggle to catch them.

Over the past month, Waikato University researcher Adam Daniel has tried to catch pest fish in Lake Serpentine, just outside Hamilton.

Hundreds of native eels and bullies have been caught, tagged and released, but the pest catfish and rudd have been in single numbers.

The pests upset the ecological balance of the lakes, making it difficult for native species to survive, said Dr Daniel.

Dr Daniel and his team need to determine whether the use of the poison rotenone would be the right way to combat the problem, but to do that they need to survey the fish. This is difficult when they cannot catch them.

Lack of pest fish in the traps did not mean they were not there, but that different methods might be needed, he said.

The Department of Conservation has caught pests using gillnets, which catch the fish by their fins as they try to swim through.

Gillnetting is not encouraged by DoC for commercial use, but is effective in stopping the pest fish without catching the native eels and bullies in the lake.

A different trap design by Dr Daniel has, however, proved successful in another Waikato farm lake.

The trap has been catching koi carp and rudd that have been plaguing Lake B near Rototuna.

Fertilisers used on farms run into the lakes and make them ideal habitats for pest fish, said Dr Daniel.

The trap caught 12 large rudd in the first few days, and was surrounded by koi carp.

Dr Daniel said the koi don’t usually go into the trap in the first couple of days, so it had been successful so far.