Changing tide for Clarence prawn industry
A RECENT study by the Marine Biodiversity Hub has assessed the potential benefits of reconnecting the shallow sub-tidal creeks that once fed Lake Wooloweyah in the lower estuary, which could boost school prawn production by up to $900 a hectare in marsh habitat and $5000 a hectare in channel habitat.
James Cook University adjunct principle research scientist Colin Creighton said the study was an attempt to identify changes to the Clarence River estuaries that have resulted in the loss of productive wetlands and salt marshes, and how they can be repaired.
"In Australia and in the Clarence we've altered our estuaries, and we've lost things like The Broadwater wetlands, saltmarshes at the bottom of the Mikolo causeways and in Shallow Channel and there's been tides changed to Wooloweyah," he said.
"Having grown up on the Clarence, it's one of the biggest estuaries and I have a passion for thinking about it and how to start repairing fishing in the Clarence.
"We want to try and understand the benefits of repairing the productivity of fishing and put it in dollar terms to understand in the clearest way the possibilities available."
Mr Creighton said their research looked mainly at school prawns because of their recognised dollar price, and because the Clarence always had a large school prawn fishing industry.
"We found that the changed tides meant most of the water when up the North Arm of Palmers Channel, and because of the changes over the years to the tides some habitats are more productive than Lake Wooloweyah simply because the tide isn't getting in like it used to," he said.
"A companion project looked at carbon sequencing to understand the diet of key species from crabs and flatheads to bream and prawns and it found their diet came from the saltmarshes, not so much from the mangroves. As a result if we can get more of that habitat back in the estuaries there will be more food and more fish.
"We also went into some of the delta parts of Lake Wooloweyah and the huge wetlands near Yuraygir Park, and if some of those areas were opened up by increasing the channels to get tide in and breaching levee walls around the wetlands, there could up up to $16,000 of extra school prawn product per hectare every year, which would mean a lot more jobs and food for other fish up the food chain."
Mr Creighton said the study would be used as a basis to make recommendations to State and Federal Governments for changes to the Clarence River estuary.
"We know the fishing industry is down, and we know we want to get jobs back into the industry, and we can do that by generating more food in the system," he said.
"We know we can probably do better in the management of caneland too. In the study we're talking about trying to optimise the output and ensure we have a win-win for everyone."