The Ministry for Primary Industries said it's trying to cut the number of undersized snapper being caught by commercial operators

A study shows 144 tonnes was hauled in from the top of the North Island to the Bay of Plenty in the year to February.

It's about three percent of the total commercial catch - and well within what's allowed.

The Ministry said while the undersized catch doesn't create concerns about sustainability, there are real benefits to reducing the number of baby snapper being caught.

It's already introduced a "move on" rule, where fishing vessels have to shift location if they're catching too many small fish.