"We believe this was a highly organised black-market ring which took in excess of 4300 crayfish with a commercial value of over $300,000 from the Mahia area in Hawke's Bay over a seven-month period," MPI's director of compliance services, Gary Orr, said in a statement.
MPI believes the crayfish were then sold on the black market in Auckland, Kawerau, Rotorua, Turangi, Gisborne, Napier, and Blenheim.
"The investigation to date has focused on gathering evidence, including surveillance of alleged offending," Orr said.
"Today's search warrants will provide further information to support the investigation. We will be gathering a number of formal statements from suspects as part of this work."
Orr said that MPI fishery officers work hard to protect fishing resources from people who seek to profit illegally.
"We hope today's development sends a strong message to others tempted by greed - that we will do everything within our powers under the Fisheries Act to protect the fishing resources owned by all New Zealanders," Orr said.
MPI is encouraging people to report suspected illegal activity through the ministry's 0800 4 POACHER number, 0800 47 62 24.
- RNZ