Australian researchers tracking life on the Great Barrier Reef said Friday they have proven a long-debated theory that fish born in marine reserves boost overall ocean stocks by dispersing widely.

The team, from the ARC Centre of Excellence for Coral Reef Studies, used DNA testing to track the spread of baby coral trout and stripey snappers from their spawning on the reef's Keppel Island marine reserve, where fishing is illegal.

"We found that the marine reserves, which cover about 28 percent of the 700 hectare (1,700 acre) reef area of the Keppels, had in fact generated half the baby fish, both inside and outside of the reserves," said lead researcher Hugo Harrison.

"The study provides conclusive evidence that fish populations in areas open to fishing can be replenished from populations within marine reserves."

Published in the scientific journal Current Biology, the study is the first to prove the sometimes contested theory that setting aside marine reserves can help restock neighbouring fishing zones, added co-author Garry Russ.

"This study in the Keppel Islands, for the first time, demonstrates that reserve networks can contribute substantially to the long-term sustainability of coral reef fisheries, and thus to food security and livelihoods in the region," said Russ, from northern Australia's James Cook University.

The Great Barrier Reef is the biggest in the world, comprising more than 3,000 individual reef systems and hundreds of tropical islands.

It is home to 1,500 fish species and 30 types of whale, dolphin and porpoise.