And when he caught his fish, he nearly got himself into more difficulty, according to Mr Sinclair.
"The PM, fishing wise, is a work in progress," he said yesterday.
"He was about to wrestle a blue cod but I managed to warn him off the idea of grabbing it on its back because the spines would've stabbed further holes in his hands.
"He had wrestled a cray and carved himself up a bit, so he won't do that again. His people management skills are certainly a lot better than his crayfish management skills."
It was Mr Key's first trip to the remote region. He came away raving about the experience in the "spectacular" southern scenery.
"He was lucky enough to spot a pod of dolphins, which was pretty cool," a spokeswoman for his office said.
"He also went on a helicopter ride over Resolution Island and up Dusky Sound which was breathtaking.
"He said it was one of those moments that really reiterated just how beautiful New Zealand is."
Snapper is the Prime Minister's favourite fish dish.
Last year, he attracted some criticism when he said Kiwis care more about snapper than the under-fire spy department, the Government Communications Security Bureau.
His spokeswoman yesterday was tight-lipped over his fishing success.
"In regards to the fishing it's fair to say the Prime Minister was 'relatively' successful but you will have to wait until the show airs early next year to see how he went."