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Carp seize the day

March 12, 2022

Carpe diem! And that’s what introduced carp (Cyprinus carpio) do! Deliberately introduced into Australian rivers in the 19th century, carp now make up 90% of the fish biomass in the Murray-Darling Basin, including the Yea River and its floodplains.

An old bushman told me once, that when floods come, the carp rush to the furthest tip of the floodwaters, relishing the new ground that the water covers, while native fish – Murray Cod, the perches and catfish – are more hesitant. As the waters begin to recede or dry up, the native fish head back to the main river while the carp keep pushing forward.

Carp make a mess of water – they feed by sucking the mud, filtering out any plant or animal matter it contains with the result that the water where carp live becomes muddy and degraded. They reduce native plant abundance and cause bank erosion, plus the muddy water is less hospitable to many native creatures.

You can see carp stuck in drying pools around the district right now, pools left by a wet Summer but a drier start to Autumn (except for the Northern states, alas!) You can see their fins exposed above the water as they not only seek food, but seek to survive in a shallowing pond.

One year, a Murray River flood filled the large Round Reed lagoon in the Guttrum forest, near Koondrook, and it was a wildlife bonanza with much breeding of waterbirds, frogs, and carp. Then the lagoon began to dry out and millions of carp were stuck while any well-trained local fish had already got out while it was safe to do so. Ducks, herons and egrets preyed on the fingerlings. Then a flotilla of pelicans flew in. They formed circles and rounded up carp into banquets. After a while, they couldn’t get any more because the only ones left were too big even for a pelican’s giant bill – carp can weigh as much as 10kg, though 4-5kg for an adult is more common.

As the water got shallower, the big carp began to flap and excavate ruts and scrapes where the water could be a bit deeper for them, though they still protruded from the top. Sea-eagles, foxes and whistling kites were preying on them. Locals from Koondrook came with trailers to grab a big carp to bury under their passionfruit vines (reported to be super fertiliser), and a pig farmer brought in a truck and pitch-forked out about 10 tonnes for his pigs.

Finally, the water was gone and there were still stinking carp lying all over the lagoon bed. The numbers were incredible! Which is not surprising when a large female can lay 1.5million eggs! Such carnage seemed to have an effect though, for when the lagoon flooded next time a few years later, I did not see many carp at all.

Seizing the day is all very well, but one should plan an escape route for when the day is over.

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