MPI district compliance manager Stephen Rudsdale said some paua were as small as 65mm , and officers seized a Toyota Hilux.
In another incident, a gatherer was caught with 54 undersized paua taken from the Whananaki area.
On the west coast, in the Hokianga, compliance officers stopped a vehicle on Waimauku Rd where the driver and two children had been diving for paua, and found 82 paua, 59 which were undersize.
Mr Rudsdale said paua were a valued resource in Northland and it was disappointing that some people's actions put the future of shellfish at risk.
"Paua don't move around much and they can easily be stripped out of a local area. With the breeding stock gone, it takes a long time to bring a paua population back."
All four men are facing serious charges under the Fisheries Act 1996 of up to $250,000.
Compliance officers are also warning people to steer clear of buying oysters on Facebook or out of the boot of a car, as they may have been illegally harvested and could make people seriously ill.
Compliance officers have dealt with a number of cases this month where people have been selling wild oysters or oysters harvested from disused farms.
Mr Rudsdale says people have no guarantee the oysters have been harvested from clean water, properly cleaned and chilled, and stored according to food safety rules.
"People are risking illnesses such as norovirus, salmonella and shigella when they buy oysters from a dodgy source. It is illegal to sell your recreational catch and carries a penalty of up to five years in prison and a fine of up to $250,000."
- People can report any suspicious fishing activity or sales confidentially to 0800 4 POACHER (0800 476 224)
