Auckland / Waikato News Index>August 2007

Auckland/Waikato August 2007

Weed spraying on Lake Karapiro
In May this year, the government agency responsible for management of the lakebed of the Waikato hydro-lakes, LINZ, sprayed herbicide over 50 hectares of aquatic weeds in Lake Karapiro.  The objective was to reduce the amount of weed drifting down the lake in preparation for the world rowing champs in 2010.  Most of the spraying occurred in the lower section of Lake Karapiro near the rowing course, but a hectare was sprayed near the Little Waipa boat ramp. The spray was very effective with the weed quickly disintegrating within a few days.  Might River Power have reported a 95% reduction in the amount of weed collecting on the intakes to the Karapiro Dam, and the rowers appear to be happy. We have had some feed back from anglers stating that fishing has been a lot easier at the Little Waipa mouth with the absence of weed.  Fishing in the lower reaches of Karapiro should also be a lot easier.

NIWA are monitoring the impact of the spraying on bullies, a small native fish, and so far there does not appear to be any reduction in numbers.  There may be some impact on the trout fishery but it will be difficult to determine.  However we will be releasing tagged fish into Karapiro next year and we will carry out at least one netting survey.  At present, there is no intention to use the spray in the upper reaches of Karapiro where most fishing occurs.

Coarse fish news
 Authorisation was recently given by Fish and Game to EJ & NJ Donald to transfer grass carp into Lake Kareta, South Kaipara Heads.  This used to be a popular tench fishery but in recent years the lake has been choked with weed.  Kareta will be heavily stocked with grass carp to remove the weed, and thereby allowing greater recreational use.

 We received several complaints from coarse angling clubs about the Waikato University using their electric fishing boat to exterminate tench and perch from Lake Panarama.  The University was on contract to the Waitakere City Council to do a presence/absence study of fish in lakes near Sturges Road.  However the reports appear to based on hearsay as the University staff involved insist that all tench and perch were returned unharmed to the water after being measured.

Didymo
Thankfully didymo still hasn’t reached the North Island. Trials in the South Island have showed that chemical control using a copper solution provides only about 90% control, and the dead didymo still remained a nuisance until it was removed by a major flood. Moreover, 250 tonnes of solution would be required to treat 4km of a small river such as the upper Waipa.  So there appears to be no cure, and we must remain vigilant in keeping didymo out of local rivers by checking, cleaning and drying our fishing gear.

University fisheries studies
The scientists at Waikato University believe that within 5-10 years they will be able to determine the presence of fish, invertebrates, and weed species in a lake or river by using a handheld probe that will examine for waterborne dna. All organisms living in a lake or river shed some of their cells, and thus dna, into the surrounding water. Therefore even a small quantity of water will have the dna of every species existing within a waterway.  The University is already using this technology to test water samples for the presence of didymo. The technology will be a great tool for fishery scientists – we can’t wait!

Hamilton fishing Competition
The Hamilton fishing competition was held over the weekend of the 25/26 September with 45 anglers fishing in the Waikato River within the boundaries of Hamilton City. In general, the fishing at Hamilton is better in Spring (October/November) when the large brown trout move up from the lower river following the whitebait. Nevertheless there were plenty of fish caught in the contest with 24 brown and one rainbow trout entered.  The largest was a 59.8 cm, 1.6 kg brown trout. 

Fishing conditions
In the Auckland region, Lake Pupuke is getting a lot of fishing pressure with anglers targeting the big fish we released back in May. We have also had quite a few enquires about Lake Ototoa which is still producing fish from the 2006 releases.

Further south, the weather hasn’t been that great over the winter months for fishing.  Although there hasn’t been any major floods, except for the Coromandel, most rivers open to winter fishing have been discoloured.  However, the Waihou and Waimakariri rivers are nearly always fishable, and both rivers have seen a lot of anglers especially in the weekends.

September is usually a month that anglers devote to checking gear and tying flies for the new season rather than fishing.  But if the weather does clear then the upper reaches of the Waimakariri could be productive and good practise for the coming season.

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