Brook trout were today removed from Pisgah Creek, giving threatened native galaxiids an increased chance to boost their numbers.
Kye Burn farmers, staff from Otago Regional Council and the Otago Fish and Game Council today carried out the trout translocation from Pisgah Creek, a tributary of the Kye Burn to the east of Ranfurly township, using a fish transportation unit.
The trout will be relocated to Coalpit Dam where the species is already present in low numbers. The work is part of a combined effort to protect numerous galaxiid species across Otago from eventual extinction while maintaining healthy sports fisheries.
The dwindling galaxiid populations, especially those fish which are non-migratory and otherwise live entirely within only a few hundred metres of some streams, are most at risk, says ORC's Team Leader Biodiversity, Pete Ravenscroft.
"Otago's galaxiid population are fragmented and are continuing to disappear; without active management, including the removal of predators, their slide towards extinction will continue, so this is a good first step," he says.
"We welcome the support of staff of Fish and Game, particularly their expertise in electric fishing and trout transfers. It's good to see the trout going to places where they will be available to anglers rather than being simply euthanised on site."
Increased protection . . .a Central Otago round head galaxiid in Pisgah Creek today
Otago Fish & Game chief executive Ian Hadland says the organisation supports the conservation of these important species.
"This is one of a small number of places in Otago where it's necessary to intervene to separate predators from the galaxiid population," Mr Hadland says.
"Translocating the trout away from sensitive galaxiid populations is an act of balancing both protection of rare native species and preserving a unique species of sports fish which anglers enjoy catching."
"Galaxiid species in Otago face threats on many fronts, including predation and habitat competition from salmonid, native predators such as eels, water abstraction, mechanical clearing of waterways and the discharge of contaminants.
"Fish & Game wants to see the issues addressed as a whole to ensure the long-term survival of threatened species."
Mr Hadland says brook trout are relatively rare across Otago but are prolific in the streams they do occupy.
"Fish & Game has no intention to let them spread their present range further, but supporting current populations in accessible locations where they already exist is something our licence holders expect of us."
ORC, with the support of the Kye Burn farmers, have removal programmes in place within four tributaries including the recently opened galaxiid sanctuary in Spec Creek.
Mr Ravenscroft says to undertake this removal work a special licence was obtained from Otago Fish and Game.
On the move . . . Otago Fish and Game Officer – Trout Hatchery Manager, Steve Dixon, with brook trout being removed from Pisgah Creek (in background) today, before transporting to Coalpit Dam, near Naseby.
ORC, alongside stakeholders including Fish and Game, is currently writing a five-year plan which will prioritise species and populations.
"We need a better understanding of the current state of Otago non-migratory galaxiids and sports fish before we can finalise the plan. The understanding of the mechanisms that are currently protecting the galaxiids from threats will provide the knowledge to make this plan fit for purpose.
"Once it is finalised and resources are confirmed, ORC will be better placed to confirm what restoration projects will be next," Mr Ravenscroft says.
Otago's non-migratory galaxiid species
Otago has 15 non-migratory galaxiid species, of which 14 are threatened; four have a threat status of Nationally Critical (Highest threat category); five with a threat status of Nationally Endangered (Second Highest) and five have threat status of Nationally Vulnerable (Third highest). Eight of these species are endemic to Otago waters. Nine are only found in Otago. There are also four whitebait species in the region.
Central Otago roundhead galaxias
The Central Otago roundhead galaxias is only found in Central Otago and nowhere else in the world. This species has a restricted distribution occurring in some tributaries of the Taieri River and Manuherekia River catchments.
The lower limit of the Central Otago roundhead galaxias in the Manuherekia catchment is Thomson's Creek, while the lower limit within the Taieri catchment is in the vicinity of Middlemarch, says ORC's Team Leader Biodiversity, Pete Ravenscroft.
"In the past 25 years freshwater ecologists have observed a 50% loss of populations and or decline of numbers across the distributional range Central Otago roundhead galaxias," he says.
The 2021 freshwater fish surveys of Thomson's Creek supported this general understanding that the Central Otago roundhead galaxias have undergone significant distributional range shrinkage, with half of the historic previously known locations having disappeared.
"The remaining populations are marginal. They are either confined to small sections of springs and or are compromised my instream pressures. These remnant populations are of increasingly value and if not protected, then these too will be lost and on-going slide into extinction will continue for this galaxiid species," he says.
The galaxiid population found in the Mawhinney Road section of the main stem of Thomson's Creek, is the healthiest of the Thomsons Creek populations, but it is confined, he says. The recent installation of the barrier prevents trout access into this pocket of galaxiids.
The remaining populations occupy small springs where the galaxiids in most parts tend to be located towards the head of these type of ecosystems.
Habitat of the Central Otago roundhead galaxias
Central Otago roundhead galaxias utilise a variety of instream habitats, larger adults occupying cover in pools and smaller subordinate adults living amongst cobble and boulders in riffle and runs.
Streams containing alluvial gravels are the most preferred habitat of the Central Otago galaxias.
The Central Otago roundhead galaxias lives for three or more years. Spawning begins in late September through to November and eggs are laid amongst porous cobble/gravel substrates at outflows of subsurface flows.
The Central Otago roundhead galaxias are found to occupy relatively low gradient streams. The species appears to only occur within a small altitudinal band of 320 - 720 metres above sea level.
Therefore, the habitat available to the Central Otago roundhead galaxias tends to be in low-gradient streams, where they are at greater risk from introduced and native predators and the impacts of agriculture.
There is also less opportunity at these lower lying elevations to encounter a naturally occurring protective barrier which prevents migration of invasive introduced species, which increases their vulnerability to predation, competition and consequently disappearance.