Hauraki Gulf Community Shellfish Monitoring

Waikato Regional Council works with communities to survey local shellfish beds. The project is part of a Hauraki Gulf Forum initiative which aims to gather information about shellfish trends over time and increase environmental awareness.

Currently, groups are monitoring shellfish beds in two Coromandel estuaries: Wharekawa (Opoutere) and Whitianga. In Wharekawa, the surveys are done by university students from the Ecoquest Education Foundation. In Whitianga, they are done by intermediate or high school students from the Mercury Bay Area School.

What’s involved

Surveys are carried out each year to look at the abundance and size of the most common kinds of intertidal shellfish, such as cockles and wedge shells. The surveys sample shellfish over a large area, using carefully developed methods and equipment so that results can be compared between sites. All shellfish are counted and measured and returned immediately to the mudflats.

Waikato Regional Council provides practical assistance and equipment to the community groups involved. This includes help with choosing the site and setting up sampling locations, as well as practical assistance on the day, and collation of the data afterwards. Survey findings are entered into a database, reported to the school or community group involved, and collated with data from other sites to inform the Hauraki Gulf Forum. Every three years the results contribute to the Hauraki Gulf State of the Environment Report.

Contact us if you are interested in setting up a shellfish monitoring group for your beach.

What the results show

In both the Wharekawa and Whitianga sites, the cockles found are generally small, with less than 5 per cent reaching harvestable size (25 mm in length). Densities are quite high and vary from year to year. Most of the variation is caused by fluctuations in the number of juveniles (less than 15 mm in length), which in some years make up more than 75 per cent of the population. The results indicate that the cockle beds are healthy and so far, no long-term declining trend has been found.

Cockles are common on intertidal flats in Waikato Region estuaries where they provide a valuable food source for birds and fish. Dense beds of cockles can filter thousands of litres of water per day, removing plankton and organic matter and improving water quality. They are sensitive to pollution and the deposition of mud from the catchment, and declining trends in abundance can be caused by environmental change or by overharvesting.

In Auckland, the Community Shellfish Monitoring has helped identify areas where cockles were declining, and monitoring results were used to support a temporary closure to cockle harvesting at Umupuia Beach and a seasonal closure to shellfish harvesting at Cockle Bay. In the Waikato Region, the results to date do not indicate any cause for concern for the two shellfish beds monitored.