Cockle stocks in Dutch coastal waters

At low tide, cockles bury themselves in sandy tidal flats in the Wadden Sea and Delta region. The cockle fishery harvests a limited portion of the total stocks by hand, while cockles are also the primary food source for shellfish-eating birds. The survey of cockle stocks therefore provides guidelines for commercial exploitation and is an indicator of the ecological situation in the region.

IMARES conducts shellfish research in Dutch coastal waters, focusing primarily on the most prevalent species. The common cockle is very widespread, and the stocks of this shellfish can vary greatly from year to year. This is often the result of low spatfall and poor winter survival.

Surveys of stocks are therefore conducted annually in all areas where cockles are expected to live, such as the Wadden Sea in the Delta region. Cockles can become several years old, but their numbers decline with age. As a result, during the survey the cockles are placed in age classes; in this way the age structure of the population can be determined at various locations.

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IMARES has developed special cockle sampling equipment to survey the stocks on the tidal flats of the Wadden Sea and in the Delta region, while disturbing the seabed as little as possible. The punch sampler and the cockle scoop are examples of such equipment. Both are operated from a boat. In addition, some cockles live in such shallow water in the tidal zone that they can only be sampled on foot during low tide with a sampling tube. This combination of sampling methods covers the entire range of the cockle, thus providing an accurate estimate of the total stocks of this shellfish.