Sharks belong in the Wadden Sea
The ideal nursery
Door Christien Boomsma
By Christien Boomsma
Christien Boomsma
Whenever ray and shark expert Guido Leurs walks into the sea in Guinea-Bissau, he always does a little dance. He calls it the ‘stingray shuffle’: instead of walking normally, he shuffles his feet, disturbing the sandy bottom.
There’s a reason he does this: it’s to drive away stingrays. These fish are prolific in the waters on Guinea-Bissau’s coast, which resemble our own Wadden Sea region. Not only does getting stung by a stingray hurt, but the animals are also venomous. Australian conservationist Steve Irwin even died after he’d been stung in the chest by a stingray.
‘To be fair, I can understand that rays don’t want anyone to step on them’, says Leurs, who’s working on his PhD research on the importance of sharks and rays to the food chain. ‘That’s just something we have to accept. We have to be careful with them.’ He feels that researchers have to realise that they’re intruding on a world they don’t belong in. Any accidents are their own fault, not the rays’.
Fear
The same goes for when a shark attacks a swimmer. ‘We’re going on vacation in their habitats’, he says. ‘Isn’t that weird? When someone is attacked by a shark in Australia, the newspapers here write about it. But if someone in Africa is attacked by a lion, it’s only covered in the local media.’
It shows how deep the fear of these animals goes. While movies like Jaws and Deep Blue Sea have certainly contributed to this, Leurs thinks it goes deeper than that. ‘Ultimately, it’s because of our fear of the water. And rightly so, because we don’t belong there.’
We’re afraid of the water, because we don’t belong there
That’s why we blame the shark when it mistakes a swimmer in Australia for a tasty morsel. ‘But when someone goes for a run through a savannah and gets attacked by a lion, we all blame them for being there in the first place.’
If Leurs has any say in it, that’s going to change. He’s been fascinated by sharks since he was fourteen and has been trying to fix their reputation for years, not through his research at the UG, but also through his work organising shark safaris to the Azores.
It’s necessary, he says. Not only are sharks amazing animals, they’re also essential to the ecosystem. But our fear of them is making us blind to that.
Wadden Sea area
Last week, Leurs and his colleagues published a study on the importance of sharks and rays to mudflats, areas like our own Wadden Sea. The role they play is much larger than people initially thought.
Sharks always prey on weak and sick animals
We tend to think of mudflats as being greatly important to birds. Numerous bird species use areas like mudflats to rest during migration, or to spend the winter. Mudflats are the ideal environment because of the rich soil life, such as shellfish, worms, and crabs. But sharks and rays are also an integral part of these tidal areas, says Leurs, based on his research in Guinea-Bissau and Mauritania.
‘They change the seabed’, says Leurs. ‘They dig holes, for example, churning up the seafloor. That impacts vegetation and can serve as hiding places for lobsters and worms.’
At the same time, they’re top predators; they’re at the top of the food chain. That means they ensure that the fish, crab, and other mudflats populations stay healthy. ‘Because they always prey on the weak and sick animals’, Leurs explains.
Finally, the presence of predators affects prey animals’ behaviour. Just like the wolf, they create a landscape of fear, says Leurs. In other words, their mere presence affects the way other animals behave. They might, for instance, avoid certain areas they consider dangerous.
Hide
But sharks and rays also need the mudflats, Leurs discovered. Smaller species and young animals use the shallow waters to hide from larger animals. ‘They’re cannibalistic’, says Leurs. ‘They also have no problem eating their own young.’
The tidelands are too dangerous for large fish, since they can easily get stuck when the water retreats. Besides that, they prefer to hunt in deeper water. ‘Many larger species of shark have to always keep moving because they can’t breathe otherwise’, says Leurs. ‘That means mudflats are ideal nurseries.’
We need to know what’s missing, so we can bring the sharks back
However, mudflats are being threatened by overfishing and declining habitats. It’s not just our own Wadden Sea that’s threatened, but also tidal zones all over the world. ‘Sure, fishermen in Guinea-Bissau and Mauritania use small boats, but there are so many more than there used to be. We’re talking really big numbers.’
Just outside the tidal zones, the large, industrial fishing boats are waiting for their catch. Sharks leaving their nursery for the open sea run the risk of ending up on someone’s plate. ‘We may not eat sharks in the Netherlands, but in other cultures, they’re an important source of protein’, says Leurs. ‘Many local communities depend on sharks and rays for their food. And let’s not forget the shark-fin trade.’
That’s bad news for sharks. Worldwide, one third of the approximately 1,200 species of shark and ray is in danger of going extinct. But when it comes to species that are known to use mudflats, it’s nearly half. ‘Mudflats themselves are also disappearing, which is a problem for the species that need them’, says Leurs. ‘According to a recent estimation, 16 percent of mudflats have disappeared since 1984.’
Fishing
Funnily enough, no one really knows the situation in our own Wadden Sea. A recent study suggests that the channels between the Wadden islands are used as nurseries, by school sharks, among others. But there are barely any sharks in the sea itself.
That’s probably because the Wadden Sea has changed a lot because of the reclamation of the Zuider Zee and intense fishing. ‘There probably used to be more sea grass that fish could use to hide’, says Leurs. ‘The mudflats themselves probably looked very different, too.’
That’s exactly why he left for Guinea-Bissau and Mauritania for his research. ‘These areas are home to so many sharks that we’re properly able to study their ecological role. It’ll also help us find out what’s missing at home, so we can bring them back.’