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Shellfish monitoring shines light on catchment health

Posted at 9:00am Wednesday 07 Apr, 2021

About 45 volunteers worked in about a dozen teams, including many young children doing hands-on science.
About 45 volunteers worked in about a dozen teams, including many young children doing hands-on science.

A community shellfish monitoring day on the Sandspit estuary on March 14 has highlighted a worrying decline in the number of cockles reaching maturity.

This is the second year that Friends of Awa Matakanakana Catchment (FOAM), supported by community volunteers, have done the monitoring. It is an initiative of the Hauraki Gulf Forum and scientists working for the forum will analyse the data collected.

FOAM committee member Mark Foster says the samples gathered revealed a range of shellfish commonly found in estuaries including wedge shells, pipi, horn shells and whelks.

“Te tuangi (cockles) were the most common and, as well as counting them, our volunteers measured each one,” Mark says. “Cockles are filter feeders and help to clean the water they live in, and they are important food sources for many marine animals. They are sensitive to pollution, environmental stress and over-harvesting and can die if they are buried too deep under sediment.

“This is why annual shellfish monitoring provides an indicator of the health of the marine environment.”

There are 21 sampling points along three lines, known as transects, at Sandspit. The longest transect is more than half a kilometre long and its farthest sampling site is close to the end of the estuary channel.

At two sample sites more than 500 live cockles were counted. The majority of these were smaller sizes between five and 20 millimetres.

“The numbers at most sites were comparable to the previous year, but the declining numbers of cockles reaching maturity is a concern,” Mark says.

FOAM has been testing water quality in the Glen Eden and Matakana rivers, that flow into the estuary, for three years. The group also tests for E.coli bacteria in the streams and Enterococci bacteria in the saline water of the rivers.

Mark says elevated levels of Enterococci in the Glen Eden estuary are becoming a concern and FOAM is in discussions with Auckland Council on more detailed investigations.

FOAM has also participated in riparian planting in the past year to support efforts to prevent erosion of the river banks.

“We are a small, hard-working committee that relies on additional volunteers to help carry out activities such as shellfish monitoring, water quality testing and riparian planting, and we plan to undertake more detailed surveys of the natural river environment this coming year.

Anyone interested in assisting FOAM's efforts can contact them through their web blog or Facebook page, alternatively email matakanakana2@gmail.com

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