We’re working with Te Arawa Lakes Trust and research agencies to manage the population of Brown Bullhead Catfish which were found in Lake Rotoiti in March 2016 and then in Lake Rotorua in December 2018.

Community volunteers, appropriately name the Catfish Killas - coordinated by Te Arawa Lakes Trust and Bay of Plenty Regional Council, have been working alongside a professional netting contractor to remove catfish from the lakes and suppress catfish numbers.  We have seen to date that netting can hold the population to a level, but netting alone is not able to decrease the population.

Catfish are a pest fish which prey on taonga species such as koura and decrease water quality by stirring sediment. Catfish are prolific breeders and to date, population estimates indicate at least 186,000 fish in Lake Rotoiti. Catfish are indiscriminate eaters and prey on most species, contributing to the decline of native species in Lakes Rotoiti and Rotorua.

Community volunteers - the Catfish Killas - coordinated by Te Arawa Lakes Trust and Bay of Plenty Regional Council have removed over 100,000 catfish from Lakes Rotoiti and Rotorua since March 2016.

The 2019-2020 season was the busiest year on record, with over 62,000 catfish being removed with nets. We have seen to date that netting can hold the population to a level, but netting alone is not able to decrease the population.

In November 2019, Bay of Plenty Regional Council commissioned NIWA to undertake a feasibility study on potential biological control methods. Modelling indicated that a high level of suppression or eradication is possible by breeding and placing sterile (infertile) male catfish in Lake Rotoiti which will disrupt the breeding of catfish already in the lake, causing the population to decrease over the long term.

The biological control method is known as “triploidy” and involves breeding catfish in a hatchery or fish farm. The eggs of the catfish are then subjected to cold temperature or pressure, which causes the resulting hatchlings to be sterile once they are fully developed. The sterile catfish are then released into the lake and disrupt the success rates of reproduction by causing the next generation of eggs in the wild to be unfertilised.

This Biocontrol is not considered to involve genetic modification by the Environmental Protection Agency (EPA) and is regulated by multiple Central Government agencies in New Zealand.

Q: How does the sterilisation work?
A: The method is known as “triploidy” and involves breeding catfish in a hatchery or fish farm. The eggs of the catfish are then subjected to cold temperature or pressure, which causes the resulting hatchlings to be sterile once they are fully developed. The sterile catfish are then released into the lake and disrupt the success rates of reproduction by causing the next generation of eggs in the wild to be unfertilised.

Q: Is biocontrol a form of genetic modification?
A:  No - this not considered genetic modification by the Environmental Protection Agency (EPA) as the method does not change or interfere with an organism's DNA.

Q: How is the method used in the aquaculture industry?
A: The method is widely used in the aquaculture industry globally and has been available for many decades overseas. Sterilising farmed fish including salmon and trout can have a number of benefits. Sterilisation can restrict environmental impacts in preventing farmed genes from being introduced into wild populations by escapees. Fish & Game have produced sterile trout in New Zealand.

Q: Are there any ecological risks associated with this biocontrol?
A: Any impact of introducing additional catfish into the lake can very quickly be offset by increasing contractor netting, and further supporting volunteer efforts to net more wild catfish. Tagging the sterilised catfish before release into the lake means that if one is subsequently captured it can be re-released to effectively continue to the depopulation process.

This method of biocontrol is also regulated by multiple agencies and will require permits and rules to comply with from the Department of Conservation and Ministry for Primary Industries.

Q: Has the sterilisation of fish ever been successful in eradicating or supressing a population anywhere else in the world?
A: Yes. This method has been applied to sea lampreys in the great lakes in the United States of America in the mid 1990’s for a period of several years and research indicates the method was successful in reducing the population.

Q: What else will Regional Council / Te Arawa Lakes Trust be doing to contain catfish numbers before the sterile catfish are ready to be released?
A: Catfish Killas and contractor netting will continue at current levels for the foreseeable future in Lake Rotoiti and Rotorua.

Additional messaging regarding taonga species

We know that catfish are having a devastating effect on kōura populations. We also know of the risk of catfish being transported to other lakes or to the Kaituna river catchment.

The method of biocontrol is an additional tool, to support existing methods. It has been applied overseas and could suppress (and possibly eventually eradicate) catfish populations in Lake Rotoiti and Lake Rotorua in the long term. Further work is needed to understand how the biocontrol method could be applied effectively within Lake Rotoiti and Rotorua.

While this method of biocontrol involves releasing additional catfish to the lake, the impacts will be off-set (as we head towards eradication we hope that wild catfish will become so rare that our catch is dominated by ‘sterile’ released fish) in Lake Rotoiti and Lake Rotorua. In the long term, however, our taonga species would recover as catfish numbers decrease.

Why not reduce the catfish population by offering a bounty?  

Previous attempts to control pests based on bounties – most notably in NZ with possums in the 1950s - have been ineffective in reducing pest populations.  By financially incentivising the capture / killing of pests it can promote a ‘harvesting’ culture where as soon as the pest starts getting hard to catch the hunters will move on to easier hunting grounds, allowing the population to recover.  In certain circumstances it can even incentivise illegal releases in new environments to ensure a ready supply of the pest can be maintained.

Is there a risk that the catfish will change gender?

Only certain families of fish species have the ability to change gender and this doesn’t include catfish. There is a paper by Berkeley University which explains it more detail.

What are the sterile fish going to eat? Will they will just eat more koura?

Sterile catfish have the same diet as fertile catfish however through the use of contractor netting and the continued efforts of the Catfish Killas the total number of catfish released will be less than the total number caught in each year. The total number of catfish likely to be released in any given year is still to be determined and forms a part of the research being undertaken to ensure that undue pressure isn’t put on koura populations. Research has already been undertaken on the impact of catfish on koura and ongoing monitoring of the koura population will continue in the lake on an ongoing basis.  

How will we stop the fertile catfish mating too?

The release of sterile male catfish cannot stop fertile catfish pairs from breeding. Each sterile male catfish can prevent the hatching of up to 6,000 catfish eggs in each breeding season when breeding with a fertile female.

The proposed method of producing sterile males achieves the same result as if they had a vasectomy. The sterilisation would not pass on or transfer to other catfish or taonga species.

Find out more

If you would like to find out more about this project or would like to be involved in the community efforts to net catfish, please contact Lucas MacDonald, Biosecurity Officer, by completing the form below, or phone 0800 884 881 ext 8428.

Lake Rotoiti catfish

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30 Jul 2020

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Project Updates

4 months ago

New rules for boat ramp users a New Zealand first

New rules to stop the spread of aquatic pests across the Bay of Plenty come in to force this summer with boat ramp users now required to self-certify that their vessels and trailers are free from freshwater fish and plant pests. 

New rules for boat ramp users a New Zealand first

New rules to stop the spread of aquatic pests across the Bay of Plenty come in to force this summer with boat ramp users now required to self-certify that their vessels and trailers are free from freshwater fish and plant pests. 

Bay of Plenty Regional Council Biosecurity Manager Greg Corbett explains that the rules contained within the Bay of Plenty Regional Pest Management Plan 2020 – 2030, which became operative on the 17th December 2020, ensure that lake users take an active role in protecting the long term health of the region's lakes and rivers.

“Ultimately everyone benefits from these new rules. Preventing the spread of aquatic pest plants and fish that can choke the lakes, making them murky and causing the decline of native species, is vital.  

“The rules themselves are very much based on common sense and are essentially an extension of the Check, Clean, Dry behaviour that has been promoted nationally for many years.

“This summer is focused on educating people on what the rules are and what is required of them before they head out on the water. Based on last year’s boat ramp checks around the Te Arawa Rotorua lakes we are confident that the new rules reflect the actions that many boat ramp users are already undertaking,” Mr Corbett said.

In addition to ensuring that vessels and trailers are free from freshwater pest fish and pest plants, occupiers of vessels must ensure that no ballast water is transported between locations and that trailers are not left in the water other than for launching or retrieval. 

Self-certification checkpoints have been set up this week at the most popular boat ramps around the  Rotorua Te Arawa lakes. The checkpoints are clearly signposted and have forms that should be completed and displayed on the dashboard of the vehicle used to launch the vessel.  

Starting from 30th January Biosecurity staff from Te Arawa Lakes Trust will be visiting the most popular boat ramps in the area to help lake users to understand the new rules and check that they are complying with them.  

ENDS

Bay of Plenty 2020 - 2030 Regional Pest Management Plan, Rule 7

To avoid the spread of freshwater fish pests and freshwater plant pests, the following provisions apply:

  1. No person shall leave boat trailers in any water body other than for the purposes of launching and/or retrieving boats.
  2. No person shall transport ballast water from any water body to any other location.
  3. All occupiers of vessels or craft entering any water body within the Bay of Plenty shall ensure their vessels or craft (including trailers) are free from freshwater pest fish and freshwater pest plants including fragments.
  4. All occupiers of vessels or craft using a boat ramp with a self-certification checkpoint must complete the supplied certification form and display it in the vehicle used to launch the vessel or craft.

This is to protect production, environmental and public values that can be adversely affected by freshwater fish pests and freshwater plant pests.

For further media information please contact media@boprc.govt.nz

5 months ago

Acoustic tracking trial in Lake Rotoiti

To try and better understand catfish behaviour, Bay of Plenty Regional Council undertook an acoustic tracking trial in Lake Rotoiti for a 13 month period from November 2018 to December 2019. Thirty catfish were tagged and then tracked, providing new insights into the behaviour of this little-studied pest.  

Acoustic tracking trial in Lake Rotoiti

To try and better understand catfish behaviour, Bay of Plenty Regional Council undertook an acoustic tracking trial in Lake Rotoiti for a 13 month period from November 2018 to December 2019. Thirty catfish were tagged and then tracked, providing new insights into the behaviour of this little-studied pest.  

The full set of data is still being analysed, however initial results provide some interesting insights. The map attached which tracks a single catfish’s tagged behaviour illustrates how highly mobile catfish are, moving significant  distances around the lake.

The full data set of research also revealed that the catfish typically don’t go further than 20 meters water depth, generally staying in deeper water during the day and coming closer to the surface in the evening. The information collected so far will initially be used to help detect new locations where catfish may be congregating  and will help to determine where  more nets should be set. Findings from the full data set should be available in the New Year.

7 months ago

Anglers delight as Fishing Season 2020 set to commence

At dawn on Thursday October 1 an armada of watercraft is expected to descend on lakes Tarawera, Rotoiti and Okataina, marking the start of the trout fishing season.

Anglers delight as Fishing Season 2020 set to commence

At dawn on Thursday October 1 an armada of watercraft is expected to descend on lakes Tarawera, Rotoiti and Okataina, marking the start of the trout fishing season.

The season opening is cause for celebration among anglers and 2020 is no exception, says Fish & Game officer Matt Osborne. 

“Opening is a great time for families to come together, enjoy the lakes and catch a trout or two in the process. It’s good for the soul,” he says.

Fish & Game staff will be monitoring the fishing and conducting licence checks, while rangers and biosecurity staff from Te Arawa Lakes Trust, Bay of Plenty Regional Council and the Department of Conservation (DOC) will be ensuring biosecurity measures are adhered to and reminding visitors to abide by the “Leave no Trace” principles of not cutting down trees, toileting appropriately and removing your rubbish.

Biosecurity staff from Te Arawa Lakes Trust will be monitoring vessels at boat ramps. Anglers are asked to ensure they have checked their fishing apparatus for pest weed fragments and fish eggs, clean the gear to kill any microscopic spores and eggs and then leave the equipment to dry before transferring to a new waterway, says Biosecurity officer Lucas McDonald.

“Catfish and multiple weed species are already present in particular Rotorua lakes and have a detrimental effect on both native fish and trout. It’s vital that we don’t exacerbate the situation by introducing new pests to the region like didymo or Koi Carp or cause the further spread of pests already here.”

Anyone found guilty of breaching the Biosecurity Act 1993 could be convicted and fined up to $5000.

DOC Supervisor Carrie Abbott says everyone wants anglers to have a safe and enjoyable time on the lakes.

“The opening of the fishing season is a positive event for anglers and it’s important that everybody plays their part in making it a success by behaving responsibly and respecting other lake users.”

Unfortunately, last year there were reports of people trespassing on private land, excessive drinking, littering and lighting fires which have the potential to get out of control and cause tragedy.

“The opening of the fishing season on October 1 is an event New Zealanders look forward to. By educating ourselves of the few simple measures we can take to all do our part, we will be ensuring the next generation get to enjoy this incredible resource like we do,” Abbott says.

Boat users can access toilets and camp at Hot Water Beach and Humphries Bay.

Covid tracking QR codes will be placed at all DOC campgrounds for contact tracing. Further information is available from www.doc.govt.nz.

–Ends–

 

trout fishing lake tarawera dusk
9 months ago

New catfish control option to be investigated

The goal of eradicating Brown Bullhead Catfish in Lakes Rotoiti and Rotorua is being given another boost with investigation into a new biological control method.

The partnership between Bay of Plenty Regional Council and the Te Arawa Lakes Trust breaks new ground in the New Zealand biosecurity sector as the parties begin investigating the option of using a biological control to significantly reduce catfish numbers.

Read more here.

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