When Herbert Schoer's blue and white fishing cutter Marlies chugs into the port at Büsum on Germany's northern coast, its hold is full of Crangon crangon, a species of shrimp found in the North Sea. The captain with the heavy northern German dialect never brings back any other catch. He's a shrimper, and has been for nearly 30 years.
This is not to say his nets don't catch other types of fish as well, as he trawls the waters off the coast of the North Sea archipelago Heligoland. Schoer's nets catch a large number of juvenile plaice, but also common dab, whiting, smelt and sprat. But all these fish, as well as mussels, starfish and shrimp that are too small, Schoer tosses back to the sea as soon as the drum-shaped sorting machine onboard the ship spits them back out. Fishery biologists estimate fish that end up being thrown back -- referred to as "discards" -- on average amount to around 60 percent of commercial fisheries' total catch.
Of these, many of the round fish species are dead by the time they reach the water again. When taken from the sea involuntarily, their swim bladders inflate and crush other organs. Fish such as plaice have an easier time surviving their stay onboard, but then often fall prey to the flocks of hungry seagulls that follow fishing boats.
According to the European Commission, up to 800,000 tons of marine animals are thrown back from fishing boats each year in the North Sea alone, amounting to around one-third of the region's entire catch. The World Wide Fund for Nature estimates the industry discards some 39 million tons globally, while nearly one-third of all fish stocks are considered overfished.
'An Immoral Waste of Resources'
The existence of EU fishing quotas for certain species means commercial fishermen also end up throwing back fish that would otherwise be marketable. Each fishery can only take in a certain amount annually of species for which it has a set quota. Anything that exceeds those limits goes back overboard. This includes fish that are too small, protected animal species and even fish species that the fishery is allowed to catch, but for which it has already reached its quota.
But this practice may soon come to an end. "Discards are an immoral waste of resources," says Ulrike Rodust, a Social Democratic Party (SPD) politician who represents the northern German state of Schleswig-Holstein in the European Parliament. That body recently agreed by a considerable majority to reform its common fisheries policy. The new policy would require fisheries operating in the EU to bring all by-catch back to shore, where it would be counted toward the fishery's quota. Zimmermann and other scientists hope that banning discards will lead to fisheries doing everything they can to keep from catching unwanted species in the first place.
The challenge then is to sort desired fish species from undesired ones while they're still in the ocean's depths. "The ocean isn't a potato field," says Peter Breckling from the German Fisheries Association. "Fish move in mixed swarms." His organization is calling on politicians to do more to foster the development of alternative fishing methods.
Fisheries have taken promising steps in this direction. Fishing vessel captains such as Schoer have invested considerable sums in selective nets, from which fish can escape more easily. "No fisherman wants by-catch," Schoer explains.
Schoer has also brought researchers onboard his vessel to address just this problem. Fishery technicians from TI in Rostock have converted the Marlies. On its starboard side, the cutter now employs a modified net known as a pulse beam trawl, while the port side pulls a traditional beam trawl. Conventional shrimp fishing involves dragging a net with 36 bobbins along the seafloor, where it flushes out shrimp. The net catches the shrimp, but also plaice and other fish. And because the net drags directly along the bottom, the fish have little chance to escape by swimming underneath it.
In the pulse beam trawl, electrodes are used to produce an electrical field. Small pulses of electricity startle the shrimp -- and only the shrimp -- which then land in the net. Plaice and other bottom-dwelling fish don't react to the electrical pulses. The net also uses fewer bobbins and barely touches the seafloor, allowing fish to swim away underneath.
"Our tests show this method reduces by-catch by around 20 percent," concludes TI scientist Daniel Stepputtis. The advantages the new technology holds for flatfish such as plaice are even greater, he adds, with fully 66 percent fewer of them ending up in the nets. Schoer also catches more shrimp while using less fuel, because his boat's equipment is no longer as heavy.
Fishery biologist Stepputtis is also testing out other selective fishing methods, and hopes the European Parliament's by-catch initiative will drum up interest. "In the past we often had to convince fisheries to try out something new," he says. "Now they're the ones approaching us."
The details of the new regulations still need to be hammered out by the European Parliament and the EU member countries' fisheries ministers, who pushed for a number of exceptions and transitional periods back in February. "But there is societal consensus that there should be a ban on discards," admits Breckling from the German Fisheries Association.
Only fisheries that conduct their operations in as environmentally friendly a way as possible can receive sustainability certification from organizations such as the Marine Stewardship Council -- and one part of this is reducing by-catch.
Stepputtis and his colleagues certainly have no shortage of potential research questions to examine, since each individual fishery has its own particular set of by-catch issues. In operations that use bottom trawls to catch shrimp and flatfish, other animals also end up getting caught in the nets as they are dragged through the water. This happens especially with fish that travel in schools, such as mackerel and sprat.
Consider the Porpoise
Then there are the fisheries whose gill nets -- stationary nets used to catch cod and herring -- end up claiming the lives of porpoises and sea birds as well. Which creatures get unintentionally caught in these nets also varies with the season and the fishing area in question. "There are no simple solutions," Stepputtis says.
He has plenty of ideas, though. For example, together with his colleague Boris Culik, Stepputtis is testing out a warning system in the Baltic Sea that would alert porpoises to a net's location. This invention looks something like an American football, but made out of black plastic. A noise source within its housing emits the same type of clicking noises that porpoises use to communicate with one another.
Porpoises orient themselves using echolocation -- but they only do so when they are near obstacles, other porpoises or predators. A porpoise swimming toward a gill net without using its echolocation is blind to the approaching danger, and can easily get entangled in the mesh and drown.
"Other researchers have deciphered specific sequences of clicks that porpoises use to warn each other," Culik explains. His device emits a series of clicks that, to a porpoise, says, "Danger, switch on your echolocation!"
Another less elaborate but similarly effective measure is the development of "intelligent" nets. Stepputtis is testing, for example, nets that include special exit windows. Large flatfish don't fit through these gaps, but smaller fish are simply able to swim out.
Even the orientation of the mesh plays a role in determining which fish end up caught and which don't. The fuller a net gets, the more the mesh constricts, until eventually even animals for whom the gaps ought to be large enough no longer fit through. Together with Polish researchers, the TI team solved the problem by simply turning the mesh 90 degrees. This simple trick was all it took to allow the mesh to retain its original width. Nets with exit windows and these so-called T90 nets have both received approval for commercial fishing use.
Biologists are also creating special nets that take advantage of the natural behavior of fish. Plaice, for example, tend to swim downward to escape danger, while cod head toward the surface. This has allowed researchers to create "topless" nets for fishermen who want to catch plaice but not cod. The front part of these nets is open at the top, leaving an escape route for the cod.
This technique has its drawbacks, though. After trying out a topless net on his cutter Glaube, plaice fisherman John Much from the northern German town of Heiligenhafen decided the device would be better described as a "fishless net." He found that not only the cod escaped, but all the rest of his fish swam away as well.