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Legacy of Yasi for Hinchinbrook Barramundi Stocks

02 July 2013

AUSTRALIA - James Cook University researchers are gaining valuable insights into the legacy Tropical Cyclone Yasi has had on barramundi fish stocks in the Hinchinbrook Channel after more than 250 tonnes of farmed barramundi escaped into the ocean.

Professor Dean Jerry, Head of Aquaculture and Deputy Director Centre for Sustainable Tropical Fisheries and Aquaculture at JCU, said researchers were using DNA pedigree technologies to determine the proportion of farmed barramundi that now were residing in the channel.

Professor Jerry said as a consequence of the cyclone in February 2011, a barramundi sea-cage farm in the Hinchinbrook Channel was completely destroyed and an estimated 250 tonnes of farm-reared barramundi escaped into the wild.

“While many saw this as a boon for fishers, immediately concerns were raised about the long-term impact these escapees would have on the genetic fitness of the wild population if they survived and were able to establish in the population,” he said.

“The issue is that hatchery-produced fish are usually highly related, exhibit low levels of genetic diversity, and are subject during artificial rearing to a completely different suite of selection pressures than may be present in the wild.

“This can produce fish which are perfect for farming, but not necessarily representative of fish in the wild.”

Honours researcher Tansyn Noble then enlisted help from local recreational and commercial fishers to catch barramundi in and adjacent to the channel and to provide small samples cut from the fins of fish so that she could extract DNA.

Professor Jerry said DNA parentage analysis was then used to determine if fish could be assigned to broodstock parents known to have been used to breed the fish stocked into the farm.

“Ms Noble’s analysis found that 30 per cent of barramundi caught by fishers were identified as having genetic origin to the hatchery broodstock and thus represented escapees,” he said.

“Alarmingly, around half the escaped farmed fish in the channel had originated from the same male and female parents.”

Professor Jerry said the researchers’ work had demonstrated the usefulness of DNA parentage analyses to identify the farm escapees.

“There is now an urgent need to learn from this unfortunate event and understand what the long-term effects large escape events involving hatchery produced barramundi will have on wild populations.

“The results of such a study would have similar relevance to occurrences of where stocked barramundi transverse spillways of impoundments in large numbers, as was seen in the Gladstone area last year as a result of overflow of Awoonga Dam.

“Despite the regular occurrences of these two types of fish escape events in Australia, there is no current information on the genetic consequences of escapees on wild barramundi”.

“The information gathered is the first of its kind in a tropical fish species and will be useful for future monitoring and provides valuable information for management of the barramundi sea-cage industry and sustainable restocking programs.”

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