Massive effort under way to eradicate bullhead catfish
Bullhead catfish have been found in the Rotorua lakes for the first time, triggering a massive response, and efforts are under way to try to contain the noxious pest to Lake Rotoiti and to eradicate it.
The incursion of catfish into the lake is regarded as serious by the various agencies responsible for the lakes and their ecology. The Bay of Plenty Regional Council is at the forefront of efforts to monitor, contain and hopefully eradicate the fish.
When it comes to invasive noxious fish the lead agency is the Ministry for Primary Industries, but also involved at various levels are the regional council, the Department of Conservation ( DoC), NIWA, Lake Ecosystem Restoration New Zealand ( LERNZ), the Rotorua Lakes Council and Fish and Game.
Much of the research involved is carried out by the University of Waikato, and Professor Brendan Hicks from the university presented an over- view of the situation in Rotoiti to a recent symposium on lakes water quality held in Rotorua.
“The first catfish was found dead next to a boat trailer at a launching ramp on Rotoiti, but the first live catfish were caught on March 16, 2016, in a weed harvester in Te Weta Bay,” said Hicks.
Two weeks later fyke nets were set in the bay, catching 52 of the fish. The netting programme continued over two months with 770 nets set over 34 nights, producing 391 catfish; 381 from Te Weta Bay. This year the netting programme, which is operated by a contractor to the regional council, recorded 3272 catfish over 68 nights, 99 per cent from Te Weta Bay. But they have also spread to Okawa Bay and the Okere Inlet.
The regional council has committed $ 200,000 a year to the catfish monitoring and eradication programme, and in April the council installed a 90m cordon across the mouth of Te Weta Bay to try and contain the catfish population.
Test netting has also been conducted in other lakes, including Lake Tarawera, with no sign of catfish.
Hicks said the brown bullhead catfish was the only specimen of the catfish family found in this country and was introduced in 1877, initially spreading to the lower Waikato River and lakes.
In 1985, the first catfish were found in Lake Taupo, triggering fears that the pests would eat young trout. But studies have shown that while they do not eat juvenile trout, they do com- Catfish can live for long periods out of water, provided they are damp, and could be unwittingly transferred to another waterway inside a boat trailer, which is probably how they got into Lake Rotoiti. One can imagine a fish swimming inside the hollow box girder at the end of a trailer, while looking for shelter. So it is vital that people check trailers carefully when travelling between lakes; not only from Rotoiti but also if moving between Lake Taupo or the Waikato River system and any other lake. The campaign to prevent the spread of didymo from the South Island is appropriate —“Check, clean, dry”. Bite times are 2.10am and 2.35pm today and 3am and 3.25pm tomorrow. More fishing action can be found at GTTackle. co. nz. pete with trout for food. It is understood that one female can produce between 13,000 and 50,000 eggs and fish over 250mm are a serious threat to koura, or native crayfish, which constitute 60 per cent of their diet in certain types of lake bottom. Young fish grow 0.5mm a day, and reach 220mm in two years.
DoC fisheries scientist Michel Dedual, based at Turangi, has studied catfish in Taupo since the 1980s, and told the symposium that catfish could damage the lake’s environment, eat small fish and eggs, compete with native fish for food and stir up the bottom, reducing visibility.
Studies employing acoustic tags allowed scientists to monitor the movement of catfish in the lake and showed that they spend most of the time in water under three metres deep.
Under the law any catfish caught must be killed, and it is also illegal to transfer or sell live catfish.
They are prized as food fish by certain cultures and may occasionally be seen in fish tanks at fish markets. In this case the retailer must have a permit, and the fish must be killed before being taken away. Fishing in close is producing good results for those chasing large snapper in the far north and the west coast. A couple of local anglers at Raglan last week stopped in only six metres of water and soon had their limits of good fish up to 7.5kg, which is 10 snapper each on that coast.
And in Northland straylining among reefs and kelp beds along the coast is producing some large specimens.
In the Hauraki Gulf, fishing has been slower, and with snapper a little lethargic in the cold water drifting with small lures and light braid tackle i s a good approach. But work- ups have been going well and this should improve as spring bites in. It is just a question of when the weather allows boats to get out wide to where the action can be found.