But there are at least encouraging signs of a recovery in the hard hit paua habitat along the Kaikoura coastline.
Around 130km of highly productive coastline from north Canterbury to Marlborough was impacted by the 2016 earthquake measuring 7.8 that resulted in widespread mortality of paua and other marine animals.
Platforms as large as a square kilometre were thrust out of the ocean.
A paua harvesting ban along large sections of the affected coast was put in place, with the full support of the industry, which has been extended to November this year.
This affects half the PAU3 (Canterbury) fishery.
Paua are a species of snail, an ancient lifeform that has survived for millions of years, yet there is much that remains unknown about their ability to repopulate locally depleted areas.
Dr Tom McCowan, a Paua Industry Council (PIC) scientist, is among those trying to fill in some of the gaps.
In the Kaikoura fishery he is drawing on data loggers, small electronic boxes attached to divers’ wetsuits, that record effort – number of dives, number and weight of paua taken, location, water temperature.
This is cross referenced with current surveys, using electronic callipers to measure every paua seen on a dive in a measured area.
The research is warranted – the highly prized delicacy has a Total Allowable Commercial Catch of 919 tonnes and returns around $36 million in exports.
“In terms of the adult biomass it’s going to be looking pretty good in quite a few areas after the closures,” McCowan said.
“But there are some areas that came up a long way and there was high mortality and it is definitely looking a bit patchy.
“Estimating biomass is notoriously difficult to do with paua but we’ve come up with a new set of methodologies using the data loggers.”
Canterbury University’s Marine Ecology Research Group has also been conducting intensive paua research along the same stretch of coast, centred on juvenile biomass surveys, with both projects funded by the Ministry for Primary Industries.
The Canterbury team have studied a variety of sites, drawn on 20 years of previous data sampling and assessed what remained of the inter-tidal paua population. How successful post-earthquake reproduction and recruitment have been and what habitats are remaining have also been quantified.
“The good news is that we are seeing clear signs of post-earthquake recruitment in the form of tiny paua from last year’s spawnings, some just a few millimetres in length,” according to marine ecologist Dr Tommaso Alestra.
“There are also many larger juveniles in these habitats from previous years’ spawnings.
“Although these will take several years to grow into harvestable sizes, there are encouraging signs that juveniles are surviving and recruiting in some places.”
In a separate PIC research project co-funded by Seafood Innovations Limited, methods to improve the significant rates that paua can grow at are being investigated in a translocation project.
Paua growth can be highly variable and some populations do not reach the minimum legal size of 125mm.
On the Chathams, the country’s most productive paua fishery where a third of the total annual catch is made, McCowan and local divers have relocated one tonne from an area where their growth is stunted to a more productive area that has been fished out.
Differences in growth rates are being measured. Translocation could become a regular practice, another tool in managing the paua population.
The beauty of the various research projects is that they benefit everyone, with paua highly sought after by recreational and customary sectors as well.