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Searching for exotics in the shrimp nets

Shrimp fishermen help biologist to monitor rare fish species

So far the shrimp fisherman Uwe Abken has had little interest in the bycatch in his nets. But recently the fisherman from the East Friesian town of Neuharlingersiel has been taking a closer look.

The fisherman and his deck hand have been recording which North Sea exotics and rare migratory fish get caught in their shrimp nets for the biologist Kai Wätjen from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association. This is a project with model character because fishermen, scientists and the environment benefit from the results.

Does the fish have a tiny spot behind its gills or is the spot missing? This will be the all important difference when shrimp fisherman Uwe Abken from the East Friesian town of Neuharlingersiel goes out on the North Sea to catch shrimps at the end of March with his cutter POLARIS. Because Abken and his deck hand Daniel Ahrens have agreed to examine their catch for rare fish species. The inquiry came from Kai Wätjen, Biologist at the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association.

Together with the German 'Verband der kleinen Hochsee- und Küstenfischerei im Landesfischereiverband Weser-Ems' he is participating in the EU project GAP 2 ( the objective of which is to bring together fishermen and science to develop a sustainable fishing strategy. For this reason Kai Wätjen went fishing with Uwe Abken and another fisherman several times last autumn to get to know their everyday work and then develop a monitoring programme which is exactly tailored to suit the work rhythm of the fishermen.

Fifteen names of species are on the list prepared by Kai Wätjen for the shrimp fishermen: these include Red List calibres such as salmon and sea trout but also the lesser known representatives of the European Flora and Fauna Habitat Directive such as the allis shad, lamprey or twait shad – the herring-like species characterised by the small gill spot. “Some of the fish look very similar; even a specialist has to look closely“, says Kai Wätjen. The biologist has drawn up identification cards to help the fishermen if they experience difficulty and has given every cutter crew a camera with time stamp and GPS function. This is intended to enable fishermen to document rare or special catches quickly and simply.

The biologist primarily hopes for one thing from the cooperation with the shrimp fishermen: “To be able to realistically estimate the fish stock of these rare species in the Wadden Sea, we scientists need more data. The fishermen go fishing virtually daily from March to December. If they were able to document the migratory fish species and exotic species in their bycatch a huge sea area could be covered at little expense“, explains Kai Wätjen.
However, the scientist is not just relying on fishermen’s’ alert eyes, photos and catch records. Whenever Uwe Abken casts the nets, a data logger is activated which is attached to the beam trawl. “It measures the depth, water temperature and the salinity for every haul so that I can later reconstruct which fish species was caught at which water temperature“, says the biologist. Given a successful implementation of this method, it could be used later on in monitoring within the scope of the European Marine Strategy Framework Directive.

The cooperation also makes sense for the fishermen. They take a sample of around 400 shrimps every time they go fishing. The animals are then measured in the laboratory and examined for the anthracnose . Kai Wätjen: “Firstly we want to know how widespread the disease is and secondly find out where the large shrimps are in the catch area at which time and how the animals react to changes in the water temperature.“ A second advantage of this concomitant research: it could advance the certification of the Wadden Sear shrimp fishing according to the standard of the Marine Stewardship Council (MSC).

During the first test runs last autumn the shrimp fishermen primarily caught small twait shads and occasional river lampreys. Now in spring, when the sun is warming the Wadden Sea, the chance ought to increase of also finding the heat-loving migrants such as striped red mullet, sardine and sand smelt. “Perhaps we might even see species which have become rare such as the snake pipefish, the weever or thornback ray and whiptail stingray“, says Kai Wätjen. The latter used to be found regularly in the Wadden Sea.

The Alfred Wegener Institute conducts research in the Arctic and Antarctic and in the high and mid-latitude oceans. The Institute coordinates German polar research and provides important infrastructure such as the research icebreaker Polarstern and research stations in the Arctic and Antarctic to the national and international scientific world. The Alfred Wegener Institute is one of the 18 research centres of the Helmholtz Association, the largest scientific organisation in Germany.

Ralf Röchert | idw
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