WHEN Chinderah fisherman John Brinsmead went fishing recently, he didn't expect to come face to face with big Mangrove Jack.
When he felt a big fish tugging on the line, he thought it was a Trevally.
It turned out to be a record weight Mangrove Jack weighing in at 12.2kg.
"It was quite a surprise," he said.
When he did a bit of research on the species online, he came across Toby Piddocke, a PhD student from the National Marine Science Centre.
Mr Piddocke is studying fish in the North Coast and was interested in 'Jack.'
"It's an iconic species on the north coast," he said.
"This is the southern end of its distribution.
"This well studied tropical fish has not been researched on the southern end, so I'm tagging Mangrove Jacks with electronic tags to monitor their behaviour."
Acoustic receivers have been placed in the rivers for the research and Mr Piddocke has tagged 49 to date.
"I'm aiming for 50," he said.
"They are a very shy fish, so not easy to spot or tag.
"Not many people catch them on line."
But it's just as well Mr Brinsmead caught the fish 'online,' as he is able to help Mr Piddocke with his research.
The study is funded by the NSW Recreational Fishing Trust using fishing licence money.