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An enthusiastic group of students from Horizon School participated in the annual shellfish monitoring session at Sandspit on November 24, organised by Friends of Awa Matakanakana (FOAM).
Students from Years 9 and 10 made up the teams that collected, counted and measured shellfish at each of the 25 sample sites during the two-and-a-half hours before and after low tide.
They were supported by FOAM members and school staff.
The session started with a karakia by Matthew Williams, from Ngati Manuhiri, who told the students that water was a taonga of huge importance to iwi, and that enhancing the health and wellbeing of waterways should be an important priority for everyone.
A range of shellfish species inhabit the estuary at Sandspit including tuangi (cockles), whelks, nutshells, pipi, wedge and horn shells.
FOAM committee member Mark Foster says the mahi students carried out during the morning involved carefully digging a 100mm deep sample of sand and placing it into a frame. The frame’s contents were then rinsed in seawater and the empty shells removed so that the various species of shellfish could be counted.
“Only the tuangi are measured for the main purpose of comparing the data to previous years’ numbers and sizes,” Foster says.
“Tuangi are found just below the sediment surface, so that their short siphons can extend up and into the water column for feeding.
“They can move up to 1.5m along the shore during each tidal cycle by crawling. Tuangi are filter feeders and help to clean the water they live in and they are important food sources for other marine animals.
When they are in high densities, such as at Sandspit, they can have a positive effect on water clarity.
“They are sensitive to a number of things including environmental stresses, such as pollution and over-harvesting and also, they can die if they are buried too deep under sediment.”
Foster says that this year’s monitoring showed that the numbers of mature tuangi at Sandspit appears to have increased a little in the past year. However, despite having the potential to reach 50mm in size, very few cockles have matured beyond 30mm in the last three years. The smaller, juvenile tuangi numbers are remaining fairly constant, but those between 20mm and 30mm have decreased this year.
Data from the monitoring is forwarded to Auckland Council so that scientists can examine it in detail.
The results also contribute to the Hauraki Gulf Forum’s State of the Gulf report, which is published every three years.
“Shellfish monitoring is just one important activity that is helping FOAM to gauge the health of the ecosystem across the catchment, which includes the Matakana and Glen Eden Rivers and the Sandspit estuary.”
Anyone interested in finding out more can visit the Friends of Awa Matakanakana website and follow the group’s Facebook page.
