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Concerns over the release of grass carp to control weed in North Otago irrigation canals have been raised by the Otago Conservation Board, but as reporter Sarah Marquet finds out, there is more to the story.
Weed-eating grass carp do not carry diseases that could affect native fish and cannot be removed from irrigation canals without somebody trespassing, those behind the release of the fish into North Otago irrigation canals say.
They were responding to concerns of the Otago Conservation Board, publicly raised at its two most recent meetings.
The board was opposed to the release of the fish, despite the Department of Conservation (Doc) giving consent, citing two main reasons at recent meetings - suggestions a fungus the fish could carry could affect native galaxiids, and that people could transfer the carp to other waterways.
The only way the fish could be spread to other waterways was if ''someone trespassed and was malicious'', North Otago Irrigation Company chief executive Robyn Wells said.
The fish had been released into two of the company's three canals, both of which were fenced and on private property.
She said despite Doc giving the company permission to release the fish, the company had chosen ''to go with a mechanical screen [to remove weed from the third canal] at the point where there was public access, and only add the carp to our own canals on private land''.
New Zealand Waterways Restoration founding director Gray Jamieson has also spoken out against the board's comments.
The waterways company, headed by Mr Jamieson and son Blair, was established in 2004 but the pair had been breeding and supplying fish since 1996, when they were granted a licence by Doc and the Government.
He said he was adamant the fish did not carry a fungus and he was ''frustrated'' with the board for raising concerns that were ''not substantiated in any way''.
''The biggest problem is that our fish are confused with koi carp, which are a noxious pest and do carry diseases.''
The suggestion they could carry a fungus came from conservation board member Jim Williams, who had been given the information by a University of Otago fish biologist. He said the scientist told him the carp were susceptible to a fungus that grows on the skin and was particularly severe in juveniles.
He was concerned because it was a fungus that had never been tested on galaxiids.
Mr Jamieson said the only time the carp could develop a fungus would be as a secondary infection after being attacked by a bird or eel, and while all fish carried some form of disease, ''they [grass carp] do not have any diseases that can affect anything else''.
Years of research by the Ministry of Agriculture and Fisheries (now Ministry for Primary Industries), and other organisations such as the National Institute for Atmospheric Research (NIWA), had been devoted to the fish after they were brought to New Zealand in 1966, due to their ability to control aquatic plants. The Jamiesons' company now leases the carp out to companies and organisations around the country, including Biosecurity New Zealand, which was its biggest customer, he said.
The conservation board's submission to Doc in June shows concerns about the possibility of the fish breeding and spreading to other waterways.
Documents provided to the Otago Daily Times by New Zealand Waterways Restoration operations manager Blair Jamieson show he sent a response to the board with relevant answers, including that the fish had never bred naturally in New Zealand and would not do so in the irrigation canals, as the water would be too cold.
The board replied to Mr Jamieson's response, saying it ''contained a considerable amount of additional information, which we have found useful and supplies most of the detail we thought was lacking in the original application''. One of the concerns, around water temperature at the release site, was not addressed but ''if we are to believe the references cited, then it would appear not to be a problem''.
''We would like to state on the record that the temperature will not be an issue for the grass carp in regards to their function and purpose,'' Mr Jamieson said in an additional response which was not noted on the board's correspondence register but was sent on July 5.
The board raised issues of fungus and people removing and transferring the fish to other waterways at its September meeting, and again at its meeting last week. At the later meeting, the board resolved to write to the New Zealand Conservation Authority, Doc's advisory body, expressing concern at the process of granting release consent.
Speaking to the ODT this week board chairman Gordon Bailey said it appeared the authority had not taken into account the board's views when it made the decision to permit the release of the fish, which was why the board was concerned.
''And if they did, it was not relayed to the board.''
He said the board meetings were ''generally open to the public and board members are entitled to discuss [their opinions]''.
The fish were released last week and once the population was established, it was expected to reduce weed volumes by about two-thirds, Ms Wells said.
''This year we will have an opportunity to assess both potential solutions [fish and screens] to managing weed and will reassess at the end of the season to see which technology presents the greatest efficacy,'' she said.
She said of the options available - manual labour, chemicals, dredging and mechanical - the company felt the use of fish was ''the most environmentally elegant''.
The Jamiesons said that was a commonly felt sentiment, including by the Ministry of Primary Industries and the National Institute of Atmospheric Research.