About a square kilometre of mudflats are exposed at low tide in Pauatahanui Inlet, and every three years 31 teams of volunteers dig quadrats around the shores of the inlet to count the numbers of cockles at different tidal heights (images: A. Ballance)
Every three years, more than a hundred volunteers descend on Pauatahanui Inlet near Porirua for a few hours of digging and sieving in the intertidal. They’re counting cockles out on the mudflats, as part of a long-running citizen science project organised by the Guardians of Pauatahanui Inlet.
In 1976 Oceanographic Institute of DSIR carried out a systematic survey of cockles in both the intertidal and subtidal areas of the inlet, and estimated that the intertidal population of cockles was well over 50 million (the population estimate range was 438-608 million). By 1992, when the Guardians of Pauatahanui Inlet organised the first recount, numbers had more than halved (population estimate range 146-214 million). Over that period there was significant sediment run-off into the inlet as a result of subdivision development on the inlet’s shores. Since then the cockle population appears to have stabilised and perhaps increased, although a wide margin of error means the results are not statistically significant.
Alison Ballance heads out to the shallow estuary at low tide, to join the counters in the 8th cockle survey, held in December 2013, and she talks with fisheries biologist Keith Michael from NIWA, and retired marine ecologist John Wells from the Guardians of Pauatahanui Inlet, to find out why they’re counting these common bivalves, and what that tells them about the health of the ecosystem.
The cockle survey is part of a wider project to restore the health of the Porirua Harbour and catchment, of which Pauatahanui Inlet is a part.