Fisheries giant Talley's has been fined close to $100,000 after a crewman was decapitated onboard a vessel which was fishing in the Kiribati Exclusive Economic Zone.

Leighton Muir died when a rope snapped back while it was hauling in a net full of tuna in July 2014.

The rope had snapped three weeks before Mr Muir died but, rather than replace it, a knot was tied and it continued to be used.

Talley’s pleaded guilty to a charge laid by Maritime New Zealand and was today fined $74,000 and ordered to pay the 24-year-old's family $21,000 in reparation.

Maritime NZ general manager maritime compliance Harry Hawthorn said it was a horrific accident, and clearly there were issues to be addressed.

"The fact that the rope was not replaced when it broke previously and the fact that the victim was in the snapback zone area were deciding factors for us to prosecute."

He said since the accident his team has been working with Talley's to improve its safety systems - including rope management and exposure of crew members to snapback zones.

The snapback zone is an area where crew are at high risk if a rope breaks.