More Sharks in Dutch Waters, Researchers Are Catching 50 a Day per Boat
Researchers say thousands of sharks now swim off the Dutch coast, up sharply from years ago, with anglers sometimes catching 50 a day per boat. Though the most common species is harmless to people.
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Most people do not associate the Netherlands with sharks, but they are there, and there are more of them every year. Researchers say thousands of sharks now swim in the waters off the Dutch coast, a striking increase from a decade or so ago.
Fifty a day per boat
The clearest sign of the change comes from the anglers who take part in a long-running research project. “Where at the beginning we maybe caught fifty sharks during the whole three-day study each year, we now sometimes catch fifty per participating boat in a single day,” said Niels Brevé, a biologist at the Dutch Sport Fishing Federation (Sportvisserij Nederland). “There must really be thousands swimming off the coast now.”
Fifteen years ago, hardly any sharks were seen off the coast of Zeeland, in the southwest of the country. Today, around ten different species live in Dutch waters, most commonly the starry smooth-hound (in Dutch, the gevlekte gladde haai).
No need to worry
The first question people tend to ask is whether these sharks are dangerous. They are not. The starry smooth-hound has no sharp teeth, only small, flat ones, which it uses to eat crabs, shrimp, worms and other shellfish. It poses no threat to swimmers, and researchers say handling the animals to study them is safe too. Some of the other visitors are even more surprising and just as harmless: basking sharks, which can grow to around ten metres long, have also been recorded, and they eat only plankton.
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Tag and release
The sharks are being studied through a project called Shark-a-tag, run since 2009 by Sportvisserij Nederland together with Wageningen University and the Dutch Charter Boat Association. Over three days each year, sport fishers catch sharks using a simple baited hook, then measure them and fit a small tag, or sometimes a satellite transmitter, before releasing them back into the sea. When a tagged shark is later caught again, the finder can report where it was and the number on its tag. Over the past twelve years, more than 5,000 sharks have been tagged this way.
What the sharks reveal
The tags have revealed a clear pattern. In winter, female sharks head south, some as far as the Bay of Biscay or the coast of Spain, while the largest males move north towards Scotland and Norway. In spring, they return, often to almost exactly the same spot where they were first tagged. In summer, many females stay near the Oosterschelde, a tidal inlet in Zeeland, where researchers also catch large numbers of young sharks, or pups. That has led them to believe the area is an important nursery ground for the species.
Why it matters
Understanding where the sharks live and breed matters because it can help protect them. Worldwide, many shark species are in trouble. The starry smooth-hound appears to be doing relatively well along the Dutch coast, but another local species, the nursehound, is critically endangered. This year, the project is focusing on the young sharks in particular, so that these nursery areas can be better protected. Researchers would like fishers to release any sharks they catch, especially the youngest ones, which still need the shallow coastal waters to grow.