Most marine reserves are failing to protect fish any better than nearby areas, a landmark University of Tasmania-led study has found.
Researchers undertaking the largest study yet into the effectiveness of marine protected areas (MPAs) say nearly 60 per cent of them are not working effectively.
"We found little difference between fishes living in most MPAs and those in nearby fished areas, indicating that many MPAs are not achieving desired conservation outcomes," UTAS's Professor Graham Edgar said.
Just nine of 87 MPAs surveyed in 40 countries were working at the highest level, the study found.
The best reserves averaged eight times more fish and 14 times more sharks than fished areas.
They typically had well-enforced "no-take" rules, were more than 10 years old, relatively large and isolated from fished areas by deep water or sand.
"It is these kinds of MPAs that we need to create and at the same time retro-fit the existing MPAs that are unlikely to ever reach their conservation goals," Prof Edgar said.
"Given the huge changes now occurring out of sight under water, and our poor knowledge of exactly what is happening, and how best to deal with the various threats individually, the need for protected areas that safeguard whole communities of marine species has never been greater."
The six-year study used more than 100 volunteer divers to count the numbers and sizes of more than 2000 fish species.
Twenty-six Australia reserves were surveyed with only one, Middleton Reef near Lord Howe Island, working at the most effective level.
"Numbers of many Australian marine species have collapsed since European settlement, including some that have disappeared," Prof Edgar said.
"At present coastal zoning maps are confusing, with the few conservation gems hidden amongst protected areas that are ineffective because of inadequate regulations or poor enforcement."