Scientists say they've been able to prove for the first time that marine reserves in New Zealand are significantly boosting snapper numbers.
A genetic study of thousands of fish in and around the Goat Island Marine Reserve north of Auckland found the sanctuary is acting as a nursery.
A team from the university embarked on a huge six-year study of snapper families, the first study of its kind in this part of the world, because it's so difficult to track fish larvae.
They DNA tested 1000 adult fish from inside the Goat Island Marine Reserve and another 1000 from outside.
"There was a little electronic tag placed in the fish so that we could identify whether we were getting recaptures or not. And then there was a tiny fin clip for DNA analysis, and the fish returned back into the reserve again," said John Montgomery of Auckland University.
They then tested juvenile fish in a wider area of around 400 square kilometres and found at least 10 per cent of them were the offspring of adults in the reserve.
Scientists say that's an impressive percentage, considering the sanctuary only makes up 1.3 per cent of the testing area.
Recreational fishing groups have in the past criticised marine reserves, saying it locks up fishing areas and puts pressure on populations in surrounding waters.
But the findings show the reserve is contributing significantly to the snapper population outside its borders.