Cooperation between prawn fishers in North Western Australia and scientists has provided valuable information on an emerging species.

Red-legged banana prawns, a previously little-understood species living in the remote Joseph Bonaparte Gulf, are the focus of a valuable fishery worth $10 million each year.

The prawns make up about ten per cent of the annual prawn catch in Australia's Northern Prawn Fishery.

CSIRO researchers, funded by the Fisheries Research and Development Corporation, tagged and released 9000 prawns in March and April this year, in the hope of learning more about the biology of the prawn and the effect of fishing on its stocks.

Mr Rob Kenyon who leads the field component of the project says that in the first three months after prawns were released, fishers in the Gulf returned about 700 tagged prawns to the CSIRO researchers.

"This suggests an excellent reporting rate by the fishers," says Mr. Kenyon.

He says the level of cooperation has been very high, with tags being returned from most boats the scientists contacted.

Each tag contains a number, so it is possible to measure how much the recaptured prawns have grown since they were first tagged and released.

"As with other prawn species, females grew faster than the males. On average, the females grew about 6.5 mm in length (carapace length) in the eight weeks from the time they were released to the time they were recaptured," says Mr Kenyon. "The males only grew 3 mm in the same time."

In fishing terms, that means it takes about eight weeks for female prawns to grow from 48 to 24 count per pound.

Project co-leader Dr David Die says this is important information because it will help scientists understand the best time for harvesting the prawns.

He says the tagging experiments have also enabled the researchers to measure how far the prawns have traveled because boat operators keep records of where the tagged prawns were recaptured.

"The prawns traveled distances varying between 5 and 30 nautical miles depending on where they were first released," says Dr Die.

"Tagging experiments are the best way to get accurate information on growth, movements and death rates."

The information will not only benefit the fishers in the short term by providing them with information about when to fish. It will also enable the effect of changes in fishing pressure to be predicted - and therefore provide managers with the necessary information to manage the fishery sustainably in the long term.

"The objective is to have all tagged prawns returned to the CSIRO scientists who will be in the Gulf to collect them at the end of the season," says Dr Die.

The research will also investigate the juvenile habitats of red-legged banana prawns from the Victoria River to Cape Londonderry.

Fifty sites in the estuaries and rivers of the Joseph Bonaparte Gulf Coast have been chosen for the study.

More information:
Dr David Die, CSIRO 07 3826 7219.