Pilot project 'Sharks and rays back in the North Sea'

Between 2015 and 2020, Blue Linked was breeding coordinator of 'Sharks and rays back in the North Sea': a pilot project resulting from the Shark Action Plan of the Dutch government. The aim of the pilot was to investigate whether natural populations of sharks and rays can be strengthened by breeding these fish in large numbers in captivity and then release them into the sea.

The first target species was the thornback ray (Raja clavata) because it is not endangered and egg capsules are available through public aquariums. The results indicate that the targets have been met: more than 600 thornback rays have grown up in our hatchery to become vital animals, which after release have found their way in the sea and survive in the wild.

Innovative hatchery Blue Linked

Our innovative hatchery functioned as a pivot in the pilot project. Egg capsules of thornback rays, originating from the Dolfinarium (Harderwijk), were bred to healthy fish with a high survival rate. During this process the thornback rays were regularly weighed, measured and photographed. Protocols were developed to raise the fish successfully and to get them used to frozen food on live food. A wealth of data has been collected, which can be used for further steps in nature restoration projects where breeding techniques, monitoring and stocking are applied. With these results, Blue Linked's hatchery formed the basis for the success of this pilot project.

Egg capsules Thornback ray (Raja clavata) (photo: P. Verhoog).
Egg capsules Thornback ray (Raja clavata) (photo: P. Verhoog).
Thornback ray (Raja clavata), dorsal view (photo: P. Verhoog).
Thornback ray (Raja clavata), dorsal view (photo: P. Verhoog).
Thornback ray (Raja clavata), ventral view (photo: P. Verhoog).
Thornback ray (Raja clavata), ventral view (photo: P. Verhoog).
Attachment of a tag on a Thornback ray (photo: P. Verhoog).
Attachment of a tag on a Thornback ray (photo: P. Verhoog).

Successful stocking and monitoring

During the breeding activities on we also researched which tags are most suitable to mark the thornback rays for monitoring if they are caught again. Some of the specimens that were released in the Westerschelde also received an acoustic transmitter. The results show that the animals are able to reach the Wadden Sea and even the coast of Belgium and the United Kingdom. What a success!

Hundreds of thornback rays

A total of more than 600 thornback rays grew up in the Blue Linked hatchery. The first of these was born on May 1, 2015. More than two years later in October 2017 the first specimens were released in the Oosterschelde under a lot of media attention. And on October 3, 2020 - a day before World Animal Day - the last cultured thornback rays were given their freedom.

Strengthening natural fish populations

During the four years of the pilot project our work appeared regularly in newspapers, on radio and TV. In our hatchery we gave guided tours for the public and our rays touched many hearts. Dozens of trainees learned the tricks of the trade with great enthusiasm. We are proud to gain knowledge and experience in this way about the possibilities of strengthening natural fish populations with cultured specimens. Nowhere in the world comparable research with sharks and rays is taking place.

Partners in the pilot project 'Sharks and rays back to the North Sea' were: World Wildlife Fund, Stichting De Noordzee, Sportvisserij Nederland, Dutch Shark Society and Stichting ARK.

Highlights of the project can be found on our news page.

Or read more about the pilot in this brochure (in Dutch).