Poachers, including a known gang associate from Hamilton, were fined and had dive gear and a vehicle seized after locals alerted police to suspicious diving off Mt Paku in Tairua on Saturday.
The four divers were fined a total of $2750.
The 150 paua, 284 kina and five undersized crayfish seized were returned to the ocean.
Whangamata Sergeant Will Hamilton says the result was "down to luck and good police and MPI team work". MPI chief compliance officer fisheries, Jason Howat, says it was a warning to poachers to expect to be stopped and inspected at any time.
"People who continue to abuse our fisheries will be caught and dealt with accordingly."
Police say one of the divers, a 33-year-old Hamilton man, has been a target for police and MPI for months and is a gang associate.
A local called police on Saturday morning about the suspicious activities of a group of men at Paku Hill.
An officer found two vehicles at the site, one of which was linked to the offender.
The officer went halfway down a steep track and saw four people diving near the rocks gathering seafood and called for backup.
"A fishery officer from MPI was also present and together the officers developed a plan to safely intercept the men after their dive," Hamilton says.
"After a six-hour wait, the group emerged from diving not far from where they had parked their vehicles and were all taken into custody.
Howat says New Zealand's fisheries were protected through collaboration.
"We have a lot of coastline to protect and thank police and members of the public that report this sort of activity to us."