The three-toothed stickleback is well-known on Lake Constance – and its image is good for everything else. The invasive species is held responsible for the decline in whitefish populations, among other things. In this respect, it is good news that the number of sticklebacks has apparently decreased enormously.
Every five years, the fisheries research centre in Langenargen (D) carries out an inventory of Lake Constance on behalf of the public sector. This very special form of inventory was on the agenda again this year. On the Vorarlberg shore of Lake Constance, where many fish species have their most important ‘nursery’ thanks to the extensive reed belt, researchers and fishermen recently set out together again to make big catches.
The cause of the decline is still unclear
Everything that Lake Constance has to offer in terms of fishing was in the nets – pike, pike-perch, perch, whitefish, roach, catfish, lake trout, etc. – but the dominant species of the past few years appeared only sporadically: the stickleback. “We have caught hundreds of sticklebacks during the last few fishing operations, but now the total is less than fifty,” says Alexander Brinker, head of the Fisheries Research Center. Considering that sticklebacks made up more than 90 percent of the fish population in open water at the beginning of this year, this is a real sensation.
The neozoa were first discovered in the 1950s; aquarium fish were probably “thrown out” in Lake Constance. The species has multiplied explosively since 2012. The researchers are now faced with a major puzzle because they cannot explain the disappearance of the invasive species. There were no signs of such a decline in stock, Brinker said. He and his colleagues currently have no choice but to speculate: “The possible cause of the decimation could be a parasite or a disease.”
This is good news for the former breadfish of Lake Constance, the whitefish. Because sticklebacks feed on their spawn and larvae, among other things, and were therefore primarily responsible for the large-scale disappearance of the excellent food fish. Recently, so few whitefish were caught that a catch moratorium was even imposed for Lake Constance. There are already initial signs that the whitefish population may be recovering: “The whitefish we caught no longer looked as emaciated as in previous years.”
Recovery of whitefish stocks
Of course, it is still too early to report on any celebrations, especially since many of the background factors are still unclear. “But if the mass disappearance of sticklebacks is confirmed, this could be a real game changer for the recovery of the whitefish stocks,” says Brinker, who gives hope to all professional fishermen on Lake Constance.
Source: Krone
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