Fisheries officers with the Department of Primary Industries and Regional Development observed the two women fishing for the marine molluscs in mud flats at King Bay on the Burrup Peninsula in June last year.
The Karratha women, aged 32 and 41, jointly collected nine litres of Ark shells - far exceeding the daily bag limit of two litres per person.
In a separate matter, a 33-year-old Perth woman who was also fishing with the Karratha women was intercepted after fishing at King Bay and bringing ashore eight litres of Ark shells - six litres over the bag limit.
She was issued a fine and penalty of $1,408.30, including costs of $194.30.
DPIRD Supervising Fisheries and Marine Officer at Karratha Michael Dunne said overfishing for Ark shells was an ongoing problem and could threaten the sustainability of the mollusc stocks.
“DPIRD has fisheries compliance patrols targeting illegal fishing for Ark shells in the King Bay area, resulting in multiple infringements and prosecutions,” Mr Dunne said.
“Anyone who suspects illegal fishing activity should call FishWatch on 1800 815 507 or report the matter via the online form on Crimestoppers.”
All edible molluscs (except oysters) must be landed whole and kept in the shell until fishers are more than 200 metres inland from the high-water mark.
A Recreational Fishing from Boat Licence (RFBL) is required if you are collecting Ark shells from a powered boat, even if diving or snorkelling from the boat. No licence is required for shore-based collection.