Alasdair Kirk was fishing 14km northeast of Taiaroa Head when he hauled up what he thought was an anchor shortly after 1pm "It just came up and landed on the deck.
"I had a look at it and thought it was a bomb or something," he said.
Mr Kirk said he reported his find to police, but had to remain on his Careys Bay-based vessel until the Burnham-based New Zealand Army bomb squad arrived by road.
"I wished I threw it back in the water."
While waiting on his vessel Awarua he described the object to the Otago Daily Times as "50cm long with four fins on the end".
"It's a torpedo-shaped thing that is pretty rusty."
At 7pm two members of the squad arrived to relieve Mr Kirk of the item and from a long day aboard his vessel.
Acting Senior SergeantEd Baker said the item was declared a "dummy",most likely an old aircraft practice round.
Another similar sized item described as a "lightly barnacled and heavily corroded explosive device" was fished up earlier this year by the Carey's Bay-based fishing boat, Aurora.
The bomb squad said that item was an 11kg practice aircraft bomb, which could be fitted with a spotting charge designed to function when the bomb hits the ground and emit a bright flash and cloud of smoke.
All items recovered by the squad are removed and destroyed.
