Cockles Coming Back in Pauatahanui Inlet

The health of Pauatahanui Inlet is being restored, judging by the big increase in cockle numbers recorded in the latest survey by the Guardians of Pauatahanui Inlet (GOPI).

Cockle numbers are up 21% from 277 million to 336 million since the last survey in 2010 and have grown a massive 87% since 1995.

The Cockle Survey has been undertaken by GOPI every three years since 1992 and is analysed by National Institute of Water and Atmospheric Research (NIWA). GOPI will be reporting on the findings at its AGM tonight.

This 8th survey of the cockle population in the Pauatahanui Inlet arm of Porirua Harbour was carried out in December 2013.

Volunteers assisting GOPI came from Ngati Toa Rangatira, Greater Wellington Regional Council, Porirua City Council, Massey University, Conservation Volunteers and local residents.

The NIWA report on the survey confirmed our gut feeling on the day we carried out the survey that the number of cockles was larger than in any of our previous surveys, says GOPI Chairperson Tony Shaw.

“This is good for the cockles, but must also be an indication that the general ecological health of the Inlet is improving.”

He says a significant effort is going in to reducing contaminants and sediments entering the harbour, particularly with the implementation of the Porirua Harbour and Catchment Strategy and Action Plan on-going since 2012.

"The actions taken by Greater Wellington Regional Council, Porirua City Council, farmers and urban developers to drastically reduce the amount of sediment entering the Inlet are undoubtedly having a positive effect,” says Mr Shaw.

The cockles sampled ranged from 3mm to 40mm in length although some larger individuals measured up to 58mm in length. The numbers of juvenile cockles have also increased markedly from around 1.0% in 1992 to 16.2% in 2013.

Greater Wellington Regional Council Manager Biodiversity Tim Porteous says each survey has used the same design and methods.

“This has allowed us to make direct site, transect and tide level comparisons from survey to survey and cockle numbers are increasing at most of the sites sampled.”

There were some sites on the southern side of the Inlet where cockle numbers were lower than in the last survey in 2010, including at Seaview Road, Browns Bay and Duck Creek.

“At Browns Bay currents over the last decade have washed away the fine sediment leaving gravel and hard clay, mud has been accumulating at Duck Creek and the beach at Seaview Road was largely covered by sea lettuce,” Mr Porteous says.

“Excessive sea lettuce smothers the cockles and the current conditions at the other two sites are also not a good environment for them. It has to be remembered that the Inlet is dynamic environment so there has been improvement in some areas and deterioration in others, but overall the picture is very good.”

Porirua Harbour and Catchment Strategy and Action Plan Co-ordinator Keith Calder says this survey adds to the wealth of information being gathered about the harbour.

“While it is very early days in the implementation of the Harbour Strategy, it is pleasing to have an indication that we are heading in the right direction in reducing the sediment coming into the harbour.”

The full report by NIWA gives more detail and can be found at http://www.gopi.org.nz/cockle-survey-2/.

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