Locally extinct Yarra Pygmy Perch return to the Murray near Lake Alexandrina

The Yarra Pygmy Perch (Nannoperca obscura) is a small native fish, whose common name is derived from the Yarra River, situated at the eastern end of the species’ range, but also occurs through south-western Victoria and southern SA, as far as the Lower Lakes of the Murray River. The species is quite sensitive and is threatened by loss of habitat (drainage, diversion, groundwater decline), invasive fish and drought, and has declined since European settlement. Although the Yarra Pygmy Perch is still widely distributed, the species has been reduced to a smaller number of isolated, highly fragmented, threatened populations across the landscape.

As a result, it is is now listed as nationally endangered (IUCN and EPBC Act 1994), as well as protected and critically endangered in South Australia, where the species as been a long-standing priority for NGT. The upgraded national listing to endangered is effective as of 15 November 2023, and emerged from the SEAP Freshwater Fish listing project that NGT recently implemented.

To provide some geographic context, the map below from a paper by Michael Hammer (et al) in 2010, shows how genetic analysis has identified the threatened, outlying, lower Murray population of the Yarra Pygmy Perch as being one of four Evolutionarily Significant Units (ESUs) that make up the species’ national range.

Geographic relationships and Evolutionarily Significant Units (ESUs) in Yarra Pygmy Perch (Nannoperca obscura) samples
subjected to molecular analyses. From: Hammer, M.P., Unmack, P.J., Adams, M. et al. Phylogeographic structure in the threatened Yarra pygmy perch Nannoperca obscura (Teleostei: Percichthyidae) has major implications for declining populations. Conserv Genet 11, 213–223 (2010).

It is this western-most population area that is the subject of this article, and has been the focus of a long-running NGT recovery program. The local extinction of this sub-population was prevented by rescuing fish from the wild during the Millennium Drought, and eventually placing them into surrogate breeding ponds and dams on private property. The hope was that they could one day be released back into the wild in the lower Murray, once the drought broke.

It has taken years of hard work and dedication by many people, but numbers are now high enough at our breeding sites to enable the return of some back into the wild in SA!

On the 10th of November, NGT Senior Aquatic Ecologist Dr Sylvia Zukowski, in partnership with Murraylands and Riverland Landscape Board and supported by Dr Scotte Wedderburn from the University of Adelaide and the Ngarrindjeri Rangers, and the Department for Environment and Water’s the Living Murray team, released 1600+ Yarra Pygmy Perch into a wetland site near Lake Alexandrina, near the Murray mouth in south eastern South Australia. The little fish have been released into a series of ‘soft release’ enclosures, to keep them safe while they settle into their new environment.

You can see a few images of the release below, or learn more by reading this short ABC news article, which includes drone footage.

This project is supported by the Murraylands and Riverland Landscape Board.

Tessa Roberts