Fisheries officers have stopped a group of commercial fishers in the Thames area who were allegedly under-reporting catches and unlawfully supplying snapper.

The Ministry of Primary Industries has been investigating allegations into the unlawful trade of commercially caught fish from the lower firth of Thames into the Auckland area.

In December, 45 fishery officers and the New Zealand Police executed searches at five locations, including three residential properties across Waikato and Auckland.

During the searches over $25,000 in cash was seized along with six commercial fishing vessels and a refrigerated truck.

About 800kg of undocumented grey mullet and kahawai was located, along with 230kg of undocumented snapper.

Electronic devices including phones and computers were also seized and are undergoing analysis.

Eight people have been interviewed and could face prosecution, however, enquiries are ongoing.

It's estimated the group may have supplied in excess of 20 tonnes of un-reported fish to legitimate businesses over the past twelve months, says Andre Espinoza, MPI's team manager of fisheries compliance in the western North Island.

"There are measures in place to ensure the sustainability of our fisheries including accurate and truthful catch reporting.

'Those who don't respect the rules will be appropriately dealt with under the law."

He says fishery officers have increased patrols over the summer season and closely monitor the area, and anyone caught breaking the law can expect to be held to account.

To report any suspicious fishing activity, phone the MPI 0800 4 POACHER line – 0800 47 62 24.