Fishing: Carping on about the weather and, ahem, herpes

THE FORECAST for the weekend is lousy, with strong southerly winds and swell over two metres predicted.

The tides are getting extra push now, with new moon on Monday, so the rivers should be OK for those creatures that like plenty of run to help forage for food or to move around, especially whiting and mud crabs.

The offshore grounds are probably out and the beaches will have plenty of surf and not much sand. Beach drivers should be wary of this and keep a tide chart handy if they go.

That's unless the forecasters get it all wrong again, like they did yesterday. We cancelled a fishing trip on the back of the 30-knot winds forecast but had long faces when just a puff of a change came through.

Carp herpes

Anyhow, it gave me the chance to do a bit of homework on the CSIRO's carp herpes program, which has been in the news lately.

The CSIRO and the Invasive Animals Cooperative Research Centre, have determined after seven years of research that the Cyprinid herpesvirus 3 (CyHV-3) could significantly reduce the number of common carp.

Thought to comprise up to 90% of the fish biomass in parts of the Murray-Darling Basin, carp also infest the Richmond River in large numbers, even in quite brackish waters.

'Our' koi-carp started to appear in the river and its tributaries in the 1980s, about the same time as a farm for the breeding and sale of 'ornamental' koi carp was established.

These escapee fish multiplied gradually at first but have seriously taken over vast stretches of the middle to lower river system to become probably the second most prevalent fish in the river, behind mullet.

Carp don't just muddy the waters of our river as they turn over the bottom sediments in search of invertebrates to eat, they actually compete with native freshwater and estuarine species for the same food and even eat small fish.

Cast enough lures on the Richmond in search of bass, bream, flathead and mulloway and sooner or later you'll catch a carp on your soft plastic, crankbait, blade or even surface lure.

Get into the right area and use a popular bait like garden worms, corn kernels or bread and you can catch them one after another and still not dent the population.

The CSIRO began tests at the Australian Animal Health Laboratory at Geelong, where scientists found it damages the kidneys, skin and gills of a carp, affecting its ability to breathe.

Depending on water temperature, the virus multiplies in the fish for about seven days after infection until first signs of disease appear and then the fish dies within 24 hours.

CyHV-3 is transmitted by direct contact between fish but can also infect fish by water-borne virus.

Like all the herpes viruses, CyHV-3 is species-specific and CSIRO tests indicate that it is unlikely to leap across to a new host species.

CSIRO tests have indicated no danger to 13 native species including Murray cod, various species of perch, eels and catfish, as well as freshwater yabbies and rainbow trout. Chickens, mice, frogs, turtles and water dragons have also been tested and shown no signs of infection.

We'll get more into the details of this in coming weeks and try to ask somebody in DPI Fisheries if this research has implications for the Richmond carp population.

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