Pilchard deaths and a frog killing fungus

July 30, 1999

The worst scourge of the worlds seas in recorded history is currently consigning millions of pilchards to a watery grave.

Since it first struck in 1995, millions of pilchards have been washed up along the beaches of southern Australia.

In two outbreaks, in 1995 and then in 1998-99, huge waves of fish mortalities have swept along the coast from the south of the country, to as far as Noosa, on the east coast, and Western Australia, where fish are still dying.

Scientists at AAHL have identified a herpes-type virus that may be the cause of the deaths that are in turn impacting on the fishing industry.

"There has never been mortality to this extent within the fish population in recorded history," says Alex Hyatt.

"One hypothesis is that the virus was introduced to a naive population. It appears to have a point source and correlates though it is not proven, to an area where a large population of blue fin tuna are kept in pens.

" They have to be fed on pilohards, which are imported from overseas and dumped into the ocean there.

"The virus may be being introduced in that way, although at this stage this is just one of a number of hypotheses. There are no huge deaths of pilohards in overseas areas.

"It's possible that these overseas pilchards are immune to the virus.i But it is not just fish that are dying. Australian frogs too are underthreat from a new and mysterious disease that has resulted in population crashes, not in polluted cities, but in wilderness areas.

Research at the CSIRO laboratory, as well as at James Cook University, points the finger to a new fungal disease, a type of chytrid fungus.

A survey of sick and dying frogs found the fungus had infected 23 different species of frogs, including seven threatened species.

"The fungusis uknown to be in the soil, but it had never been seen in vertebrates before," explains Hyatt.

The fungus infects the frogs' skin, and given that frogs breathe through their skin, this appears to be fatal.

The devastating impact of the fungus on the frogs suggests it has been recently introduced to Australia.

Scientists are keen to learn where it has come from, and why frogs are now so susceptible.

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