Selwood's boat is only 1.4m by 4.5m.
"For some unknown reason he just launched himself out of the water and he must have come up four feet out of the water to clear my outboard motor and drop straight in the boat.
"There I was on all fours and he's looking at me and I'm looking at him and then he started to do the dance around and shake and I couldn't get out quick enough onto the gunnel," Selwood said.
The fisherman was able to radio for help to local marine rescue volunteers at Evans Head, the ABC reported.
Selwood was rescued and then the boat and shark retrieved.
The fisherman was treated for a swollen arm.
The shark was pulled out with a forklift and the Department of Primary Industries was to perform an autopsy on it to confirm its age and gender, the ABC reported.
Selwood was left thinking over his close encounter.
"I've had 'em come up and brush the side of my boat, I've had a white pointer swim around my boat, I've had 'em take fish off my line, but I've never had one do this," Selwood said.