Perch purge led to native population boom

November 24, 2016

Redfin Perch were eradicated from Phillips Creek Reservoir

Redfin Perch were eradicated from Phillips Creek Reservoir

The eradication of an alien fish species from a reservoir in south west Australia led to an explosion in the population of a native fish species and an increase in Marron, Murdoch University researchers have found.

Dr Stephen Beatty and Associate Professor David Morgan from the Centre for Fish and Fisheries Research believe the draining of the Phillips Creek Reservoir near Manjimup and removal of non native Redfin Perch was the reason why the endemic Western Minnow population subsequently bloomed and Marron stocks increased.

They say the approach could be adopted elsewhere depending on ecological factors and community willingness to consider conservation outcomes alongside the recreational or commercial value of alien fishes like Redfin Perch.

“The most plausible answer to the increase of Western Minnows is a release from high predation levels by the perch, which presumably preyed upon the native fish to a level that made it undetecable when we first started surveying the inhabitants of the reservoir 12 years ago,” said Dr Beatty.

The Western Minnow has a voracious appetite for mosquitos

The Western Minnow has a voracious appetite for mosquitos

“The Western Minnow is one of the most widespread and abundant native freshwater fish species in the south-west. Its presence in our waterways is very beneficial because it has a voracious appetite for mosquito larvae, pupae and adults.”

Professor Morgan added: “The Redfin Perch was introduced to Australia as an angling fish. Other introduced species in the south-west like Rainbow and Brown Trout are annually stocked into reservoirs and rivers to support recreational fishing.

“These species are known to prey on Western Minnows and other native species like Marron, an iconic recreationally fished species in the south-west.

“So there is a need to balance the the value of alien species for angling with the conservation and human-service value of these native species.”

Marron are an iconic species recreationally fished in WA

Marron are an iconic species recreationally fished in WA

The researchers conducted surveys of the reservoir’s aquatic populations a few weeks before drainings were carried out in 2004 and 2007. They also surveyed the fishes and crayfish caught while the water was pumped out. No Western Minnows were recorded at the time of the first destocking effort, but almost 1000 alien perch were removed and euthanased.

Before the second draining exercise, a Western Minnow was observed within the reservoir for the first time, with 100 captured in December 2006. During draining a month later, more than 28,000 were removed and relocated, but no perch were found. Also, the abundance of Marron was at its highest level in the January 2007 draining.

Dr Beatty and Professor Morgan said their study also suggested that artificial environments like reservoirs, if free from alien predators, had the potential to be harnessed as refuges for native fishes to offset the loss of natural aquatic habitats due to climate change and salinisation.

The study was funded by the Water Corporation and the findings were published in the Journal of Fish Biology.

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