THE Macquarie Perch (Macquaria australasica) is a fascinating Aussie native fish. This species has been described as a more upland version of the very closely related golden perch (Macquaria ambigua), and indeed they superficially look like a grey coloured version of that fish.
Prior to European settlement, Macquarie Perch were numerous and distributed widely throughout the middle to upper reaches of the upper Murray, Lachlan and Murrumbigee River systems. There are also natural populations of "maccas" in two East Coast river systems, namely the Shoalhaven and the Hawkesbury-Nepean. Scientists have deduced that, like for the east coast cods, the eastern populations of Macquarie perch managed to cross the Great Dividing Range into eastern systems through natural river capture events, perhaps as far back as 600,000 years ago.
Indeed, the natural eastern populations of Macquarie perch are almost certainly a separate species, due to their long isolation from the Murray-Darling populations. There are certainly some significant differences between the two. East Coast Macquarie perch are relative "dwarf" fish that tend to grow to a maximum size of only 18-19 cm, compared to the maximum of around 46 cm and 3.5 kg for exceptional fish from the Murray-Darling populations. There are also other differences in morphology and key life history characteristics between the two populations that mean declaration of the east coast fish as a separate species seems inevitable sometime soon.
Anglers report that East Coast Macquarie perch tend to be found well upstream in habitats above those frequented by their cousins, the Australian bass. However, today, both approved and illegal translocations of Macquarie perch have occurred, and non-natural populations have been occasionally established in certain lakes and river systems, including a self-sustaining breeding population in the middle and upper reaches of the Yarra River near Melbourne.
In the Murray-Darling populations, male perch generally reach sexual maturity in their second year of life at around 21cm long, while females mature in their third year at around 30cm, though under certain circumstances some sub-populations can mature at much smaller sizes (12-14 cm). Spawning occurs from October to December, with fish living lakes moving into tributaries to spawn. The spawning sites tend to be located at the foot of pools and the eggs drift downstream and lodge amongst gravel in riffles, not too different to the strategy employed by breeding trout.
Macquarie perch are totally protected in NSW and there are strict angling restrictions in place in other jurisdictions that mean that the vast majority of Macquarie perch caught by anglers these days are released. Nevertheless, because of their particular need for access to running water with clean gravel for spawning and egg incubation, the main threats to Macquarie perch populations stem from habitat modification such as sedimentation, clearing of riparian vegetation, construction of dams and weirs which act as barriers to migration and recolonisation, and cold-water discharges from dams which prevent successful breeding. The widespread nature of these threats in Australias river systems have resulted in these fish becoming listed as endangered species, with localised extinctions common in many parts of their former range.
Radio-tracking studies have shown that adult Macquarie perch feed mostly at dawn and dusk and at night, and tend to stay within certain home range sites during the day. Food items consist of small prey, including shrimps and aquatic insect larvae, particularly mayflies, caddis flies, midges and cladocerans. This shows they have significant dietary overlaps with introduced species such as trout and also redfin perch, both of which are also known to be carriers of the EHN virus that is known to be highly pathogenic for Macquarie perch. This is why scientists think that competition with introduced species is one of the major factors contributing to declines or extinction of Macquarie perch populations throughout certain parts of their former range. This is also why control of introduced fish species is such a high priority (together with river and riparian restoration efforts) wherever restoration of Macquarie perch populations is attempted.
NSW rec anglers are leading the way with macquarie perch restoration through their fishing trust money. Image: NSW DPI.
Its great to see angling groups heavily involved at the forefront of Macquarie perch conservation efforts. Some of the more notable achievements have included habitat rehabilitation projects such as restoring the vegetation around the banks of creeks that are key habitat for endangered natural Macquarie perch populations in several upper river catchments. More recently, restocking of Macquarie perch has also been undertaken in some areas of NSW where the original populations are known to have become locally extinct. Research has shown the stocked fish can survive, but whether they can successfully breed and become self sustaining populations remains to be seen.