Since the start of this year, four people have gone, a family of six is to depart in August and a couple also plan to quit.
Geoff Soe-Paing, who will leave with wife Eilidh and their four children, after five years on Canna, said the inability of inhabitants to buy or build property is hampering the island's long-term prospects.
But the NTS, which owns the island, has begun a feasibility study looking at all aspects of tenure - ownership, leasing and shared-equity schemes - which may help overcome the issue.
Alexander Bennett, the trust's countryside and islands group manager, north, said it offers leases of 15-20 years on properties. It does not offer houses for sale for fear they end up as holiday homes.
Mr Soe-Paing said the NTS took up custodianship of Canna 30 years ago and he would have expected issues such as tenure to have been addressed by now.