The Ministry for Primary Industries has closed down fishing operations in Napier, Hastings and Mahia suspected of black market trading.
In a statement it said one commercial fishing vessel, three recreation vessels, one tractor and 11 vehicles were seized.
MPI officers searched 22 homes, inspected commercial fishing premises and interviewed 31 people in the operation.
The Ministry said the recreational and commercial fishers were suspected of illegally selling paua and crayfish.
It involved 1.8 tonnes of paua and 600 crayfish.
MPI's compliance director Dean Baigent said the ministry had been gathering information since March last year.
"We've had someone working covertly in this area for a period of time, to increase what is a very hard nut to crack."
Mr Baigent said MPI special duties officers had become involved in the black market activities as part of the investigation. They found illegal trading of paua and crayfish which had been gathered by recreational fishers.
Some disguised their activities by using customary authorisations. These were issued by local tangata kaitiaki/tiaki but should not be used to make money.
Commercial fishing companies in Hastings and Napier were also being investigated because of their suspected involvement in the illegal trade of shell fish.
Mr Baigent said the illegal fishing put both the paua and crayfish fisheries under threat.
"It is MPI's role to ensure people are fishing by the rules and to protect New Zealand's fisheries for future generations. As this operation would indicate, it is something we take very seriously," he said.