SNH is recommending that ministers designate the South of Barra as a special area of conservation (SAC) to protect harbour seals, sandbanks and reef habitat. But many islanders fear it would restrict local boats' fishing activity. And they have not been placated by SNH saying fishing could continue on a managed basis.
Scotland's Environment Minister, Paul Wheelhouse, ordered an independent review of SNH's scientific advice on the proposal. This has been completed and a decision is expected shortly.
But the Southern Hebrides Against Marine Environmental Designations (Shamed) group argues that any review of SNH science for Sound of Barra SAC must reject the proposal.
Fisherman Angus MacLeod, who has co-ordinated opposition to SNH proposals said: "The isle of Rum has been set aside for state-managed conservation since 1958. This huge island has been used as a private outdoor laboratory for 50 years, particularly to study its red deer, but I have yet to hear this work is valued by working deer managers in Scotland. In fact, it is quite the reverse.
"Rum had also shown SNH had a lot to learn from others about sustaining human communities."
But SNH spokesman said Mr MacLeod's view of Rum was outdated "Community development is well underway on the island. We transferred ownership of the village, including land for crofts, to the community in 2010."
He added: "We are confident that the scientific case for the Sound of Barra SAC is robust. "