Reviving toheroa

Shellfish numbers have been plentiful for centuries and important kai for Northland Māori, but industrial harvesting and canning had a devastating effect on toheroa numbers.

I ngā wā o mua ko te Toheroa te tino kai a te hapū kei te tai hau-a-uru o te Ika-a-Māui e noho ana, ā, ka taonga ki a rātou. (The toheroa, was once a staple in the diet of hapū on the west coast of Te Ika-a-Māui and considered a taonga.)

Dr Ocean Mercier

The toheroa population collapsed after years of overharvesting.

For three decades, a ban on harvesting has been in place, and the kai that once nourished hapū all along the coast is no longer making it to the dinner table.

Te whāinga – the goal

There was a need to find out how abundant the toheroa were historically and what their population size is at present. The Toheroa Abundance Project was formed.

Since local tangata whenua held a great deal of understanding about this taonga, kuia and kaumātua were asked to share their understandings – their mātauranga .

Two local men, Barry Searle and Jim Te Tuhi, have been instrumental in establishing the toheroa project. They have been working to save the toheroa population in Northland over many years and are now working with the Ministry for Primary Industries (MPI) to re-establish a growing toheroa population.

E tino tika ana hoki kia whai kaitiaki te toheroa. (And it’s kaitiaki that the toheroa are in desperate need of.)

Dr Ocean Mercier

Finding solutions and a way forward

The relationships formed with the local people as part of this project have been a crucial part of its success. Many kuia and kaumātua living along the beach were interviewed and asked what they felt was impacting on the toheroa populations. They were also asked if they wanted to help sample toheroa populations along the beach.

Locals have learned skills from the scientists about how to gather data in a beach survey investigation. This is important for the ongoing work of the project. The beach is being mapped by tangata whenua, looking for signs of the toheroa and counting and measuring the shellfish inside sample areas.

Kua whakarewa tikanga aromatawai ia, hei taunaki i te mātauranga ki te mana o te pūtaiao. (He’s introduced survey methods that back up mātauranga with hard science.)

Dr Ocean Mercier

Toheroa are naturally aggregated into dense beds, so you can go many kilometres and find no toheroa but then find a dense bed with lots of individuals crammed in together. It is important to know where these beds are likely to be so the team can concentrate their sampling efforts around those areas.

Combining iwi knowledge with the results of the recent surveys, the Toheroa Abundance Project group has highlighted some of the potential issues that are affecting the toheroa’s re-establishment as a sustainable source of kai.

The goal is that the information gathered from the project is communicated widely and that it influences decisions about how the area is managed. It is also important to educate children in schools about the history and the biology of the toheroa, particularly the factors that affect toheroa and how our human behaviour influences the population growth. While we are still some time away from being able to harvest toheroa again, it’s hoped that the population can be rebuilt and toheroa will once again be a delicacy we can all enjoy.

Sampling techniques – the quadrat and transect

The sampling techniques used by the toheroa research team are a common way of collecting data in a specific area and are often used together. Some transect lines, like the one in this project, are GPS-mapped locations. There is no guesswork when returning to collect data at different time intervals, whether seasonally or each year.

For the Toheroa Abundance Project, the sampling involves running a line from high water down to the low water mark, called the transect line. Holes are dug at set intervals along the transect line. If it is over a toheroa bed, digging of the quadrats occurs at 5-metre intervals. At each position along the transect, a 500 x 500 mm square quadrat is placed. This ensures the same unit area of sand from each position is sampled along the transect line.

In a high-density bed of toheroa, spades may damage the toheroa, so the holes are dug by hand to minimise damage. Holes are dug down to a depth of 300 mm. This will ensure the sample of the beach will contain the toheroa and perhaps tuatua (another species of shellfish found in this area)

The sample is placed in a trolley with a sieve in the bottom and is rinsed out in the surf, leaving the shellfish behind on the sieve. Each individual quadrat sample identifies, counts, measures and records the shellfish found. The data can be then recorded on a map of the beach, and estimates can be made of the total toheroa population size.