Pest fish discovery at Lake Tomarata “shocks” ARC

The suspected discovery of illegally-introduced koi carp in Lake Tomarata has left Auckland Regional Council officials “shocked and extremely disappointed”.

Group manager monitoring and research Grant Barnes says he was well aware of the problem in nearby Lake Spectacle, but was sceptical when Northern Matters contacted him for comment on the Lake Tomarata situation.

In a return phone call an hour later, Mr Barnes said he was very disappointed to confirm that the carp were indeed in the lake.

“Once again we see the selfishness of a few people impacting on the health of a precious resource with significant recreational value,” Mr Barnes said.

He said he would be alerting biosecurity to the discovery and the ARC would now look at a response. In the meantime, he commended the effort being made by the Lake Tomarata Management Committee.

The committee, led by keen fisherman and Fish & Game honorary ranger Craig Stevens, has started to regularly net the lake.

“Illegally-introduced fish damage the ecology of the lake by rooting around the bottom while feeding,” Craig says. “This disturbs sediment, destroys native aquatic plants and leads to a decline in water quality, which is only “average” according to Auckland Regional Council (ARC) tests. Koi and rudd also breed prolifically, with a mature Koi carp able to produce in excess of a million eggs.”

Craig says catching Koi may require a different netting method because they are bottom-dwellers and much stronger than the rudd.

According to ARC studies, water clarity in the lake has deteriorated significantly since 2004. In 1998, clarity was more than 3.5 metres. This has fallen to about 0.5 metres.

The ARC blames the poor water clarity on the collapse of the submerged aquatic plant community. It believes the plants may recover if the pest fish can be controlled.

The Tomarata residents plan to continue netting each week until Christmas, and Craig hopes that as the water gets warmer, more fish will be easier to catch as they swim closer to the surface. Numbers of fish in the 14 nets set during the group’s first attempt last month were pleasing, but not as many as Craig had hoped.

Inevitably, some trout were also brought in, but Craig says they only served to highlight the need for the operation.

“They were pretty miserable specimens compared to their counterparts in other areas, such as the Kai Iwi Lakes.

“Some of them were about two years old, and only a third of the size and weight you’d expect. They’re really not thriving here at present.”

Trout were last released into the lake last year. Fish and Game fisheries manager Ben Wilson says releases are usually done every two years and a decision on whether or not to re-stock Lake Tomarata would not be made until next May.

Craig believes that Fish and Game is unlikely to make any further releases due to the decline in water quality and loss of aquatic plants.

Information: Craig Stevens on 431 5907.

Sam Gardner, Isobel Greenwood, Margaret Fishlock and Craig Stevens with some of the intruders netted in the clean-up.