Regional council chairman David MacLeod added a late item to Tuesday's policy and planning committee meeting, calling on officers to seek out evidence for a decline in kaimoana over time.
"I personally have anecdotal evidence from when I was younger through to today that kaimoana stocks are worse off."
He said staff needed to work out how bad the problem was, what the implications were, and what measures the regional council could take, perhaps with the Ministry for Primary Industries.
Councillor Neil Walker said three possible causes of decline needed checking: overfishing, pollution and natural causes such as sand drift.
An iwi representative on the committee, Bonita Bigham, said the state of kaimoana was "a huge issue".
"The number of cars coming to the end of Mānihi Rd and Arawhata Rd, the busloads coming, it is a crisis. Regardless of the science, I think the issue is that there is a crisis."
Bigham said the hapū of Taranaki iwi needed to be included in the council investigation.
"Could we please invite Taranaki iwi to come and speak to their rationale for the rāhui, and share their mātauranga (knowledge and understanding)?"
MacLeod's call for an investigation was passed unanimously by the committee.
The hapū of Ōrimupiko are planning to apply for a legal ban under the Fisheries Act, especially for pāua, that could last for two years and be further renewed.
Other hapū that had placed rāhui were also considering a legal ban.
Ōrimupiko kaitiaki o te moana (coastal guardian) Jack Davey said hapū were already moving to survey the coast.
"Our next step is to have a look at which areas have been exhausted, and after two years we might be able to say only particular areas need to be put back under protection."
Separately to the extensive west coast rāhui, Ngāruahine's Ngāti Hāua hapū in July placed a rāhui on their 7km coastline further south, from Wahamoko Stream near Oeo to Ōtakeho Stream.
Ngāti Hāua kaitiaki Sid Ngātai said they also want a Fisheries Act ban to bolster the rāhui.
"Iwi need to start shutting it down with the assistance of the Crown – shut it down for two years at least."
Despite being 70 years old, Ngātai said he does a stocktake of the hapū's 18 named reefs every six weeks in summer, taking along rangatahi (young people) to pass on knowledge.
"It's really good, since I get to talk with my rangatahi on the hīkoi (stocktake walk) ... I talk to them about how I was taught by my koroua, my pāhake (elders)."
He said the reefs had been "hammered".
"We've got to make a sacrifice now, or there's not going to be anything left for our mokopuna."
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