THE conservation of dolphins is under threat with alarming numbers of the young dying in South Australian waters, it was claimed yesterday.

The impact of a record pilchard catch last year also should be investigated for any link to the deaths.

SA Museum Curator of Mammals, Dr Catherine Kemper, said post-mortem examinations on the mammals have found 90 per cent have been infected with nematodes.

Most of the infected dolphins were from Gulf St Vincent, Investigator Strait and southern Spencer Gulf. "What we know is that all of a sudden a year and a half ago the number of young dead common dolphins with lung nematodes spiked up," Dr Kemper said.

"What usually happens with parasites like that is that animals are probably stressed in some other way like some environmental stress.

"There may be there's some oceanographic changes going on but I suspect that it may have more to do with the food chain. Last year the pilchard industry took a record number, 50,000 tonnes, of pilchards in this State and they didn't really know what affect that would have on the environment."