Farm run-off and people driving their vehicles along the beach are being investigated as possible causes of a decline in shellfish numbers and diversity along the Horowhenua coast.
Ngati Raukawa ki te Tonga and Cawthron scientists have conducted a 3-day survey and discovered once abudant toheroa have virtually disappeared.
Dr Huhana Smith, of the Taiao Raukawa Trust, says the concern was triggered two years ago after shellfish found near the mouth of the Waiwiri stream were unfit to eat.
She says Ngati Raukawa wants to work with local authorities, farmers and the public to restore and increase kaimoana numbers.
Dr Smith of Ngati Tukorehe says they are waiting for the final results to come back so they can talk with the district and regional councils and the public about what can be done for the sake of kaimoana along the coastline.