Scientists at NIWA hope an artificial undersea habitat might help increase stocks of some popular varieties of fish.
Plastic seagrass mats made to resemble thick blades of grass have been laid in Whangapoua harbour off the Coromandel peninsula.
An estimated 10,000 young fish, including trevally and snapper, will be attracted to the 6000-square-metre fake bed of grass.
Ecologist Mark Morrison says hundreds of fish will be tagged and their growth and survival rate tracked.
Dr Morrison expects the thick grass will protect the fish from predators.
The tagged fish will be measured in March or April, before they migrate for winter.