Fish population survey: Large inventory on the Elbe-Lübeck Canal

The report from the LSFH-SH, Landessportfischerverband Schleswig-Holstein eV:

In the past few weeks we have once again thoroughly examined the fish stocks on the Elbe-Lübeck Canal. The Federal Waterways and Shipping Administration (WSV) has entrusted us with the care and use of this exciting body of water for fishing. As part of conservation, we conduct regular fish stock surveys to document what is going on in this exciting body of water.

6 days and 60 kilometers

For this purpose, we carry out a six-day fishing trip every year on the more than 60 kilometers between Lübeck and Lauenburg. The aim is to find out how the stocks of fish species in the canal are developing and, above all, how efficient and sustainable our annual eel stock is. The investigations are carried out by the Conservation Community Water System Kiel Canal, which looks after all of our waters leased from the WSV in terms of fisheries biology. And because the results on the eel in particular are of considerable importance and of general interest, the work is financially supported with funds from the fishing levy of the state of Schleswig-Holstein.

*The main focus of fishing is on the condition of the eel stock in the Elbe-Lübeck Canal.*
*Photo: LSFV SH*

The fish are caught with an electric fishing device that is used from the boat. In addition, a close-meshed trammel network is set up at 22 stations parallel to the bank. It is intended to prevent larger fish from fleeing from the shore areas into deeper water when the boat approaches. This method works particularly well for eels.

*A trammel net placed parallel to the bank catches the fish fleeing from the current or the boat.*
*Photo: LSFV SH*

Elbe-Lübeck Canal: Always on the move

10 years ago the catfish came

But of course a lot of other fish species are also caught. In this way, we can recognize trends and have already observed several unexpected developments in the past. “The catfish population has increased significantly for about 10 years. When we caught the first one in 2008, we were over the moon. It is now common and is caught by anglers everywhere in the canal,” reports LSFV fisheries biologist Rüdiger Neukamm.

Catfish have been caught almost everywhere in the canal for a number of years - including when we fish.
Photo: LSFV SH

A large stock of perch

In terms of fish, the ELK is a dynamic body of water where stocks are constantly changing and moving. It is therefore also important that we have a view of the body of water in order to counteract any negative developments. The last few years have seen significant changes in predatory fish: the canal used to be very good water for zander. At the moment, unfortunately, only a few are caught by the anglers. As a result, the stock of pike has increased. The stock of perch, on the other hand, is very stable. He patrols along the edges in good sizes and in large numbers. We are currently considering whether we should make another attempt to rebuild the zander stock through stocking measures. We will report here again on the respective development.

*Perch are caught in good sizes by anglers and also by the LSFV biologists.*
*Photo: LSFV SH*

Chub instead of Aland

This year we saw a few more exciting trends. "The Döbel is the new Aland!" We've never had so many Döbel in the ELK. On the other hand, we were almost completely missing the ide in our catches. Perhaps something is shifting here in the species. Let's see if the anglers' catches confirm this assumption. The bream population has evidently continued to decline in recent years, but the roach seems to have recovered somewhat. The reason for the decline in white fish stocks is still unknown to us. A shift in spawning times due to climate change, a reduction in plankton due to the sometimes massive occurrence of the quagga mussel or the eating away of spawn and young fish by black-mouthed gobies and perch are under discussion.

*Young black-mouthed gobies abound. They are a reliable food source for perch and eel. But how does their feeding pressure affect the offspring of the species?*
*Photo: LSFV SH*

Well grown carp stock

We were also able to catch a few young carp and tench, but the large specimens can hardly be caught with our methods. However, carp anglers regularly catch very large and healthy carp, including grass carp in specimens well over 20 kilograms.

*The eel is absolutely dangerous for crayfish and black-mouthed gobies. The head of the riprap can keep the two invasive species well in check.*
*Photo: LSFV SH*

What also interests our LSFV biologists are the interactions between individual species. For example, what happens to the other whitefish stocks when the chub actually invades the Channel? The future will probably tell. What can already be examined is the influence of the eel on the immigrant species of crayfish and black-mouthed goby. Both live mainly in the gap system of the riprap - exactly where the eel also feels at home. Bad for the peaceful neighborhood: the eel likes to eat the goby! And the eel also likes to breastfeed the crayfish. The occupied eels thus assume an important function in the regulation of non-native species.

*As if from a picture book: a fat eel next to camber crab and black-mouthed gobies on the electronic device.*
*Photo: LSFV SH*

Even the first impression of the fishing and the first count show that our eel stock is bearing heavy fruit. We were able to catch even more eel than in previous years and the size composition of the catch also gave reason to be happy. Between 8 and 93 centimeters there were good quantities of all age and size classes. Apparently the eel gets along very well in the ELK.

We also caught small eels in abundance. All size classes were represented between 8 and over 90 centimetres.
Photo: LSFV SH

“Without stocking, there would be almost no eels here at all. But the animals definitely belong here. Based on the catches and due to the proximity to the sea, with no other obstacles to migration, we can also assume that a significant proportion of the fish will migrate to the sea unscathed when the time comes.” Rüdiger Neukamm and Mattias Hempel are satisfied with the results of the this year's fishing and are positive about the future of fishing in the Channel. “It is a body of water in which you have to constantly adapt to new conditions and species. But this movement also makes the channel interesting again and again and offers fishing opportunities that we hardly have anywhere else in the country. The condition of the eels is really gratifying and reassures us that what we are doing here is good and right.”