Silver Perch - Conservation

Conservation

Silver perch have declined close to the point of extinction in the wild. Only one sizeable, viable population remains in the wild in the central reaches of the Murray River. Silver perch are bred extensively in aquaculture but these domesticated strains are of little use in ensuring the species survival in the wild.

Reasons for their catastrophic decline are not clear. Dams, weirs and river regulation and the virtual removal of spring floods does appear to have removed the conditions silver perch need to breed and recruit successfully on a large scale. Weirs are also believed to impact on migrations of spawning adults and juveniles, and it is suspected many drifting eggs and larvae are killed in the fall as they pass over weirs. A recent study that has proven an extremely high mortality rate for golden perch and Murray cod larvae passing through undershot weirs means Silver perch larvae passing through these structures almost certainly experience a high mortality rate as well.

It is not widely appreciated that silver perch eggs sink without significant water current — silver perch eggs are often inaccurately described as simply being pelagic ("floating"). This means that silver perch eggs may often settle onto the substrate in the wild and should perhaps be considered benthic in most circumstances rather than pelagic. This interesting fact may be a factor in their recent serious declines; Silver perch may rely on their eggs settling onto clean well oxygenated substrates of coarse sediments. In this era of flow regulation and flood curtailment by dams (which remove the flood events that remove fine sediment) and chronic siltation from poor agricultural practices and carp, silver perch eggs may now frequently land in anoxic fine sediment and organic matter and fail to survive.

Suspicions are also mounting that there is serious competition for food between introduced carp and silver perch at larval, juvenile and adult stages. Competition at the larval stage is considered the most serious. Indeed, suspicions are mounting that introduced carp are having very large impacts on a number of Murray-Darling native fish species due to competition at the larval stage, and that these impacts have so far been vastly underestimated.