The shellfish fishing industry in Dutch coastal waters is based on annually changing numbers and sizes of razor clams. The razor clam population size determines how many fishing permits are issued and how big the fishing quota is. IMARES monitors the populations of commercial shellfish species in Dutch North Sea coastal waters on an annual basis.
Razor clams are the most important target species in the Dutch shellfish fishing industry in the North Sea coastal zone. The razor clam is a non-native species originally from North America which arrived in the North Sea at the end of the 20th century and which now exists in large numbers off the Dutch coast. As the razor clam population increased, the indigenous surf clams decreased in number, causing commercial fishing of surf clams to decline. The fishing industry turned its attention to the new species, and today nearly the entire razor clam catch is exported to Mediterranean countries.
In order to sustainably manage the commercial fishing of wild shellfish populations, it is important to know the size and mass of a population and how the population develops over time. This can be difficult to determine because of the large distribution range and because the population can vary widely from place to place and from year to year. For this reason, IMARES carries out annual population measurements at approximately 800 sample locations along the entire Dutch coast using special fishing gear designed for sampling. Data is recorded for all shellfish species found during measurements. The study shows the changes to the populations of all species, not just the economically valuable species. The trends seen in the shellfish populations are also an indicator of the ecological condition of the Dutch coastal waters.