Great Eastern cod story
  |  First Published: October 2003

Southern Cross University researchers are fighting to save the eastern freshwater cod. The species is considered endangered and looks to be as rare as the snow leopard.

Once abundant in the Clarence and Richmond rivers, eastern cod numbers are now thought to be in the low thousands.

“The main population is condensed in small fragmented populations in the Clarence River system," said Anthony Moore, Research Fellow at Southern Cross University. "There are also small restocked populations in the Richmond River, but they may not prove be viable over time, despite many years of restocking."

SCU researchers have just been successful in securing additional funding to continue research on the species. Cathy Nock, a PhD student based at the Centre for Animal Conservation Genetics, SCU and Gavin Butler, an SCU student based at NSW Fisheries in Grafton, have recently commenced further work on the genetics and ecology of the eastern cod.

A collaboration between NSW Fisheries, Booma Fisheries and a community group called Project Bigfish have led the way with conservation fish stocking. These efforts are likely to have saved the species' decline in many areas and re-established populations in areas they were wiped out. However, preliminary research at SCU indicates that there may be a better way to breed and stock the fish. The data suggests that genetic diversity is not being maintained during the artificial breeding process.

"This is likely to be caused by using too few parents, a problem created due to the low numbers of wild fish left," Ms Nock said. "Restocking can result in reduced genetic diversity. There is also plenty of evidence worldwide to suggest that restocked fish are not as vigorous as remnant fish. We suspect the restocked cod in the Richmond are not spawning. They just exist, dependent on restocking for their survival."

Ms Nock is using DNA markers to look at changes over time, the evolutionary process within the species, and the relationship of eastern cod to its nearest relatives.

She is also determining genetic diversity in the cod samples collected by the team and NSW Fisheries, which includes 300 wild samples, and 100 known hatchery fish. She is comparing genetic diversity in those samples with the Murray cod, which has a much bigger range, a much bigger population.

"Depending on how successful the markers are, we may be able to distinguish stocked fish from remnant fish," Ms Nock said. "While this type of research has never been undertaken on Australian native fish, genetic markers have been used in the salmon family, to identify restocked fish, and how much restocking contributes to the gene pool in the long term."

Recent collaborative data from NSW Fisheries and SCU surveys indicate that illegal fishing is a major threat to species survival. One reason the cod has been taken by local fishers in great numbers over the years is the fish's aggressive nature. In its habitat, the cod is at the top of the food chain and very territorial.

The team at SCU is advising fishers not to catch or keep the cod. It's not only illegal, but could further damage the cod's slim chance of survival. They advise anglers who accidentally catch them to return them to the water immediately.

"The other main cause for the decline in cod numbers is deterioration of water quality from mining and bushfires, over a very short period," Mr Butler said. "When the railway went through early last century the workers routinely dynamited rivers for food. Siltation, due to inappropriate clearing and farming practices, is a factor that has probably stopped them coming back. Basically, a lot of bad luck."

"Unfortunately all endemic freshwater cod are under threat. If you remove an animal that is top of the food chain, that must impact on the rest of the ecosystem. The only hope for the fish is through further research and community education." - Kath Duncan

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