Although they are at the top of the food chain in the world’s oceans, they can do nothing against fishing nets. Sharks are having a hard time of it, especially in the northeastern Atlantic on the European continental shelf. Joint research carried out by 17 institutes including the Netherlands Institute for Fisheries Research (RIVO) shows that nearly all shark species are suffering badly.
“There is one exception to the rule. Dog sharks are capable of surviving for more than an hour out of water,” comments Heessen. But most sharks are very vulnerable to fishing activities. The marine biologists base their sombre outlook on samples taken from the catches landed in harbours from the Azores to Norway. The numbers of sharks have clearly declined in the last few decades. They estimate for example that only five percent of the original spiny dogfish population remains. A problem, however, is that in European harbours no distinction is made between the different shark types when the catch is registered. In the North Sea alone there are five different species. Improving the registration of sharks caught is one of the recommendations made by Heessen and his colleagues to the EU that is currently preparing an action plan for rays and sharks at the request of the FAO.
Heessen is currently trying to specify in more detail the vulnerability of the different species. One of the weaknesses of sharks in comparison with other commercially caught fish such as mackerel, herring and cod, is that they have relatively few young. They only produce one or two offspring per year, and these take a long time to mature. In a natural ecosystem, where there is no human interference, this is not a problem, but where large-scale fishing takes place this has serious consequences. Heessen: “It is inevitable that older, sexually mature are caught, and that has a big impact on population numbers.” The variety of species is also threatened. “Rare species disappear completely and more common species become rare.”
Heessen already has ideas on the measures that need to be implemented to ensure a return to healthy shark populations, and he is involved in developing the EU action plan. “It’s probably a good idea to close off certain areas of the North East Atlantic for shark and ray fishing, for example the western North Sea off the English coast.” But deep-sea species also need protecting from fishers. “The French and Irish fishers that work to the west of the British Isles are going deeper and deeper, leading to whole areas that will become empty.”
Heessen is not optimistic about reducing the numbers of sharks and rays in by-catches. “Fishers are unlikely to easily accept a reduction in their freedom by making certain areas off-limits to them. But these measures are necessary if we are to prevent the total disappearance of sharks in European coastal waters.”