Thünen-Institute
Ocean

Sustainable Fishing Re-population Program: New Trawl has Loopholes and Escape Window

The cod to the Baltic Sea. But not only the existence of the animals is threatened. They also fishermen. Rostock scientists have developed a new trawl, which would help man and animal. What distinguishes it from the usual networks? We tell you on the next page.

Professional fishermen earlier pleased with thick cod on the net without having a bad conscience, they have nowadays rather mixed feelings at the sight. Why? Because they know that just the large, old fish are particularly important for the reproduction of stocks: A ten-year cod females lay up to 40 times as many eggs as a young, become just sexually mature animal. And then the eggs of older fish also of better quality.

A solution to protect the elderly and large fish, scientists of the Thünen-Institute for Baltic  in Rostock have now worked out. Their ideal conceptions: The catch should be, mathematically, distributed according to a bell curve especially the middle-size classes should be caught while the small as of the large animals only a few in the net.

Loopholes for small fish helps to re-grow population

To allow small fish to escape, can be relatively easily implemented the codend by the appropriate mesh size and shape in the end area of the trawl. Otherwise, it looks at big fish. Since the fishing technician of Thünen Institute had a few thoughts to make more.

Out come is a grid built at the end of the network of leading upwards at an angle, parallel bars, which directs the large cod to escape window. Fish are so large that they do not fit through the mesh, they are more or less forced to leave the network through the top window.

With the research vessel Soleá, stung the scientists in Lake and tested the new network type. For this they enveloped the codend with another network, there gathered the small fish that had slipped through the cracks. A safety net was attached also to the top flight window at the front of the net. And then, the researchers have counted: how many fish could escape and ended up as many on the net as fishing.

Then, the data on the basis of various statistical models were analyzed. The result: It is in principle possible to align the cod fishing selectively for desired size classes. The key control factors for the shape of the bell curve that describes the percentage of small, medium and large fish in the catch, have a spacing of bars in the grid and on the other hand, the mesh sizes in the codend.

Thünen-Institute

Dr. Daniel Stepputtis, head of the fisheries working group and survey technique in the Thünen-Institut: “the results achieved so far are promising.” Was the researchers particularly important to show that “the ways to design networks that allow the sustainable use of fish stocks, are still not reached its pinnacle”. With regard to the Baltic Sea is pushing the time. Because right now the EU has revised the quota for cod in the Baltic Sea: In the West drops the catch by 56% compared to 2016, in the eastern Baltic Sea by 25%. A tough break for the professional fishermen.

Another problem in the Baltic Sea: 10,000 fishing nets lost each year

Another problem in the Baltic Sea: 10,000 fishing nets alone there will be lost each year, tear away in the storm, and become a deadly trap for whales and fish at the bottom of the sea. Environmentalists want to now carry this so-called ghost fishing. Pull with ships, the harrows behind. There are already first experiences.

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