Trawlermen features fishing-boat crews from the North-east who speak in Doric. Producers feared no-one outside Aberdeen would be able to understand them, so decided to use subtitles.
However, the move has come under fire.
The MSP for Banff and Buchan, Stewart Stevenson, said: "People will be able to understand what's being said. The subtitles are completely unnecessary.
"I think if we're going to discriminate on the matter of subtitles, then we should subtitle every regional accent," the MSP said.
"I remember trying to watch the first episode of EastEnders and switching it off because I couldn't understand what was being said."
Trawlermen is a fly-on-the wall documentary which gives an insight into the tough and sometimes dangerous world of fishermen.
Skipper Jimmy Buchan, 46, who owns prawn trawler The Amity II, is one of the stars.
The father of two, of Peterhead in Aberdeenshire, was told to try to make the series as realistic as possible, so he did not attempt to change his strong accent.
He is shown talking in Doric as he takes his crew into some risky situations as they struggle to make a living.
The film-makers have tried to make things clearer with subtitles, most commonly found in foreign films. A BBC spokeswoman said: "The subtitles are a result of a number of factors, like engine noise and machinery noise, coming together with what the trawlermen themselves described as a local accent that 'can be hard to understand'."