Surveys in the Marlborough Sounds show a growing number of blue cod are getting bigger since cod fishing was banned in the inner Sounds last October.
A marine biologist contracted by the Department of Conservation Bob Davidson says surveys at 10 sites show the number of cod over the legal size of 30 centimetres is up, although overall numbers are not.
But Mr Davidson says it would be a mistake to quickly re-open the entire fishery.
He says it took four to five years for numbers of large cod to increase substantially after a reserve was created at Long Island.
