They fear the limit on catches will be reached earlier than normal and the fishery will be closed by September.
Western Isles Fishermen's Association said management measures should have been put in place to reduce the impact on smaller west coast crews.
The Scottish government said it was aware of the concerns.
Association secretary Duncan MacInnes said the government had not carried out a risk assessment on allowing larger vessels into the Minch.
The Scottish government said it was aware of industry concerns about "unusually intense" fishing off the west of Scotland and possible implications for the quota.
A spokesman said a lack of prawns in North Sea fishing grounds had caused some displacement of fishing activities into the west.
He said Marine Scotland was monitoring the situation carefully.
Marine Scotland has also agreed to take forward discussions with industry experts on any likely action to ease pressure on the quota.