Pūtangitangi (Paradise Shelduck) and ducklings at Opunake Beach, New Zealand. Photo: Dave Young 2008, Wikimedia Commons
Otago Fish and Game is continuing to monitor wetlands and estuaries near the Waikouaiti wastewater treatment plant, where more than 1000 waterfowl infected with avian botulism have died.
The outbreak of the bacterial disease avian botulism in Otago was followed by another suspected outbreak in Timaru.
The majority of the dead birds collected in Otago were paradise shelduck, a native taonga species which traditionally used oxidation ponds at the treatment plant as a moulting site.
Dead bird species also included native grey teal, mallard, Canada goose, black swan and black-backed gull.
Otago Fish and Game staff were monitoring areas including Waikouaiti Estuary, Hawkesbury Lagoon and Merton Arm to see if the disease had spread further.
"Dead birds have been found within 80 metres of the perimeter of the Waikouaiti wastewater treatment plant, which was to be expected, and a few individual dead birds in the wider area, but at this stage none of further concern," a spokesperson said.
"We are pleased the DCC is taking a proactive role in removing dead birds to avoid further spread of the outbreak."
Fish and Game said it had requested information from the Dunedin City Council (DCC) about the council's monitoring and the functioning of the Waikouaiti facility, to see whether it may have contributed to the outbreak.
"We will be asking district councils across the region to look at their management plans for wastewater treatment plants to ensure everything is being done to minimise the risk and severity of harm to wildlife caused by avian botulism," a spokesperson said.
"Our primary concern is maintaining the health and sustainability of native and introduced species under our management. We will be keeping a close eye on the situation and monitoring for further dead wildlife.
"There is a possibility this could impact on game bird hunting in the North Otago area, and the potential threat to other bird populations and the commercial poultry industry can't be understated."
Wildlife rescuers were dealing with a second suspected outbreak of avian botulism after dozens of dead and sick birds were retrieved from Timaru's Washdyke Lagoon on Monday.
Alan Parker of Avian Rescue Otago said the symptoms identified in the birds - such as ascending paralysis - were consistent with botulism.
The Ministry for Primary Industries said dead birds collected in Timaru would be tested for avian botulism.
A wildlife vet said the outbreaks of botulism among birds are becoming more common in the South Island due to poor water quality and the warming climate.
Brett Gartrell from Massey University told Checkpoint the disease is caused by toxins released by bacteria growing in warm, nitrogen-rich water.
"The toxin itself stays in dead birds and maggots that feed off of the dead birds are unaffected by the toxins... but anything that feeds on the maggots or feeds off the dead birds can get a lethal dose of the toxin so the disease can keep rolling along like that."
He said outbreaks are relatively common in the North Island and there is currently an outbreak in Lake Horowhenua in the North Island.
The disease will continue to be a problem while nitrogen loads in water are allowed to remain high, Gartrell said.
He said symptoms like paralysis will show up first, with the weakening in the bird's hind legs.
"As it gets worse, their legs get weak and eventually their head droops and they die because they can't move their chest muscles and can't breathe anymore... it's a pretty horrific death," he said.
Similarly, if anyone is concerned their dog may have contracted the disease by consuming a dead bird, or the maggots that have come into contact with it, the early signs are wobbliness to the point of not being able to co-ordinate "themselves and particularly in the back legs first", Gartrell said.
Anyone who sees three or more sick or dead wild birds in a group is advised to report it immediately to Biosecurity New Zealand's Exotic Pest and Disease Hotline on 0800 80 99 66.
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