Sacks of undersized and shucked paua have been discovered in a cave on the Hawke's Bay coast.

The kaimoana was found on Blackhead Beach last week during checks on vehicles in relation to reports from local residents of suspicious vehicles and activities.

A vehicle was stopped by police and fisheries officers leaving the beach following reports three people were seen carrying sacks believed to be full of seafood.

Two people in the vehicle were spoken to and a third person was spoken with on Blackhead Beach.

One person was arrested on matters unrelated to the recovery of the paua, which is now the subject of an investigation into what is believed to be a commercial operation.

The reports of suspicious activity coincide with a rise in farm and household thefts in the area.

What was found:

• Sacks containing 39 undersized paua • 160 shucked paua, also believed to be undersized

In a separate event at Kairakau Beach, four people were spoken to and 97 paua were seized by staff.

Ninety four of the paua were undersized, while six undersized rock lobster were also seized.

All four people spoken to face prosecution.

With the recent good weather and clearing sea conditions, there has been an increase in illegal fishing on the coast.