An Auckland man has landed a bill for possibly the most expensive meal of paua ever, after being fined $8500 for buying the shellfish on the black market.

The man was one of six people sentenced in the Manukau District Court on Friday for Fisheries Act offences. All were convicted and ordered to pay fines ranging from between $1500 and $8500.

A man considered the lead diver, who illegally took almost half a tonne of paua, was sentenced to eight months' home detention and 150 hours' community service. His associate was fined $3000 plus court costs of $130.

The Ministry for Primary Industries (MPI) started investigating a Northland-based kina poaching operation in January 2015.

MPI's northern region team manager of compliance investigations, Simon Anderson, said two separate operations began after inquiries revealed more offenders, operating out of the Auckland and Coromandel areas, who were also illegally taking and selling paua.

"We subsequently exercised search warrants across the Auckland region focusing on the alleged divers and the buyers of illegally taken paua," Anderson said.

"Large quantities of paua were seized along with cell phones belonging to the alleged offenders.

"Charges were laid in early 2016 with all offenders pleading guilty."

He said three more people would be dealt with in the courts soon.

Anderson said there was no excuse for this sort of offending.

"If everybody went around taking more than their fair share of a resource such as paua, there would be nothing left for future generations.

"Paua is enjoyed by a great many New Zealanders. It is a valuable resource and its sustainability will become an issue if this sort of irresponsible and illegal behaviour continues.

"Our investigators and compliance offices did an outstanding job in detecting this offending and ensured those responsible and involved in what was an elaborate operation, were held to account."