Trigging and the Common cockle

In 2003 byelaws were passed in order to protect the common cockle Cerastoderma edule from overexploitation in Cornish estuaries. It is important to maintain a healthy breeding population and it was decided that the recommendation of a minimum collection size of 20mm, about the size of a 20p piece, would assist in this aim together with a ban on harvesting by mechanical means such as suction dredgers.

Although suction dredgers are unlikely to be used in the HVMCA the practice of trigging or cockle collection by hand-raking on Good Fridays has continued and the Helford MC Group members have observed the triggers at work!

This information has been reviewed by Rhiannon Mather on behalf of the Group and she has summarised her findings as follows:

"Over the last 10 years the Helford Voluntary Marine Conservation Area Group has carried out a series of informal surveys on Good Friday at the main cockle beds of the Helford Estuary at Bar Beach, Treath and Gillan. These surveys are aimed at providing some monitoring of the number of people trigging and the approximate number of cockles being removed from the beds as a result. The surveys have been spurred on by worries of the cockle populations of the Helford River being in
decline, a view shared by many of the local triggers.

Surveys of 1996, 1999, 2003, 2004 and 2006 have been examined and combined with studies performed by the Environment Agency for the Helford area. Findings indicate the number of people trigging each year to have altered little over the last 10-year period, and the sources of triggers to have remained much the same.

It is estimated that an average of 17-gallons of cockles has been removed from Bar Beach each Good Friday. The surveys of 1996, 1999 and 2006 indicate a 20% decrease in the number of cockles being removed from Bar Beach in the last 10 years, although it is not yet established whether the cockle population has definitely declined. For this to be determined further
survey work is required, measuring the cockle population of the area, and examining the age structure of the beds. New data would be particularly useful to investigate any effect that the 20 mm minimum size for collection has had on the cockle
populations as Jones (2000) suggested that applying this minimum size limit might improve recruitment of
some cockles by 60%."

I hope that one day we may find resources to repeat the detailed fieldwork in the earlier studies.

Pamela E Tompsett

Extract from HVMCA newsletter No.33 Autumn 2006