Chatham Islands, New Zealand

The Chatham Island mudfish looks so different to its relatives in mainland New Zealand that its discovery in 1994 resulted in a case of mistaken identity.

Charles Mitchell, who discovered it in Lake Tuku a Taupo while undertaking an ecological assessment for the Chatham Island Electricity Limited Trust, originally described it as belonging to the whitebait group (Galaxiidae). But further investigation by Dr Bob McDowall in 2004 revealed it to be a mudfish, most closely related to the Canterbury mudfish. This suggests they shared a common migratory ancestor before traversing the 850km of ocean to the Chathams and becoming landlocked and losing the migratory phase.

Because the Chathams mudfish lives in open waters, rather than the swamp habitat typically occupied by other native mainland New Zealand mudfish (Neochanna), it has retained fins that the other species have lost, and more ‘stream-like' characteristics than the other more ‘eel-like' mudfish species. Several of the mainland New Zealand mudfish species can also burrow into the soil when their wetland habitat dry out in summer and remain there motionless, until the water returns. It is possible that the Chathams mudfish have lost this ability due to living in a lake habitat, as they have been observed to air-gulp at the surface when under stress.

Further survey work by the Department of Conservation in 2001 and 2007 found the Chatham Island mudfish in Lakes Rakeinui and Rangatapu. Extensive freshwater surveys were also undertaken on Pitt Island, but no mudfish were found there.

Because it is native to the Chathams and found at just three sites, the Chatham Islands mudfish is classified ‘At Risk' and could become extinct if these habitats were modified or destroyed. Threats include fire, disturbance, or introduction of pest fish such as koi carp, gambusia, rudd or other exotic fish. To date, the only freshwater exotic animals on the island are goldfish, whistling frog and southern bell frog. Their effects on Chatham's mudfish are unknown, and care needs to be taken to prevent their further spread.

The department is running two yearly surveys on the Chathams to try and locate new populations of mudfish and to monitor the three known populations to ensure they are stable and doing well. Other information is also collected to improve our knowledge of these fish, including fish length and weight, maturity, health, diet through collection of invertebrates in the area; and fin clips for ongoing genetic analysis.

This work has been achieved only through the support of landowners Abner Nielsen, Ron and Ollie Seymour, Bruce and Liz Tuanui, Robert and Jan Holmes, Neville Day and the Chatham Island Conservation Board.