Steven Robertson, 25, fell overboard from scallop dredger St Amant off the coast of Anglesey, North Wales, in January 2012.
The condition and safety standards of the boat were criticised in a report, but Mr Robertson was not wearing a life jacket and his body was never recovered.
His partner Megan Willdig was pregnant with their first child at the time and is still feeling the effects of his loss. Without a body, she has not been able to register Mr Robertson's death, hold a funeral or put his name on their daughter Ava's birth certificate.
Ms Willdig is now backing a campaign to get all fishermen to wear a life jacket.
The 21-year-old, from Dalbeattie, in Dumfries and Galloway, said: "We will never know if wearing a life jacket would have saved Steven's life, but we do know that if he was wearing a life jacket, they would have been much more likely to have found his body.
"At first, no body being found gives you hope - and you keep holding on to the dream that he is going to be found safe and well somewhere. But as time goes on, no body just makes the grief even worse.
"There is no closure. You can't say goodbye at a proper funeral. You don't have a death certificate so you can't do the administrative things you need to do like close bank accounts. I couldn't even put Steven's name on Ava's birth certificate.
"I think a lot of fishermen believe a life jacket won't actually save their life if they fall overboard, but they don't think about how wearing a life jacket might make things much easier for their families if the worst does happen."
Fishing is one of the most dangerous jobs, according to research by industry body Seafish, which shows almost 100 fishermen have lost their lives in the past decade.
The latest figures from the Marine Accident Investigation Branch also showed there were 260 accidents involving UK fishermen in 2012, with 44 serious injuries and six deaths. A survey of 100 fishermen by Seafish found more than half agreed their job was dangerous, but only a quarter regularly wore a life jacket at sea.
The coastguard, RNLI, the Fishermen's Mission and the Fishing Industry Safety Group are working to provide life jackets to every commercial fisherman in the UK. So far, around 7000 have been distributed in Scotland, Northern Ireland and parts of England and Wales, with the initiative continuing throughout this year.
Monty Halls, who has presented TV shows including Great Ocean Adventures and Great Escapes, is fronting the life jacket campaign.
He said: "Fishermen are our last, true, hunter-gatherers and the profession comes with inherent dangers. The research that Seafish conducted highlighted that UK fishermen know their work can be dangerous and they even acknowledged that their families worry about them whilst they're working. Yet a large number are not wearing the appropriate safety equipment.
"If you were in a car, you would wear a seatbelt. The same should go when you're at sea."
Simon Potten, head of safety and training at Seafish, said: "Fishing safety is a concern and fatalities are unacceptable. A personal flotation device can save a life and it is disappointing that such a high number of fishermen put themselves in additional danger by not using them."