The Bodensee: Effects of Exploitation and Eutrophication on the Salmonid Community

Abstract

The upper basin or Obersee of the Bodensee still retains all the fish species described more than four centuries ago, though rapid changes have recently been noted in many aspects of the fish community and of the Bodensee ecosystem. Though a variety of non-native species have been introduced, including a number of European and North American salmonids, none has become a prominent part of the community. The famous Blaufelchen, a pelagic coregonine, has recently been threatened by a combination of increasingly intensive exploitation, beginning at a low minimum size, compounded by an increasing growth rate of the species due to low population density, and due to increased planktonic food as a result of eutrophication. Consequently, by the early 1960s, the fishery came to exploit large yearlings, and few Blaufelchen survived to spawn. Eutrophication has reached a stage that is marginal to a number of deeper, benthic coregonines and char. Cyprinids, usually inshore, have expanded greatly, have invaded the pelagic habitat, and are subject to periodic mass mortalities. Other of man's effects are identified as are management measures now in practice.

The influence of eutrophication and population biomass on common whitefish (Coregonus lavaretus) growth — the Lake Constance example revisited

“…The common whitefish (Coregonus lavaretus) is a species of great commercial importance in many prealpine lakes in central Europe (Nümann 1972;Gerdeaux 2004), as are other species of the genus Coregonus in lakes, rivers, and estuaries of northern Eurasia and North America (Price et al 2003;Hoff and Todd 2004;Salonen and Mutenia 2004). Any major changes in coregonid yields, therefore, attract the immediate attention of fishermen and managers and challenge fishery scientists to explore the likely reasons and eventually to recommend appropriate measures to stabilize yields.…”

“…The most dramatic changes in coregonid growth in central European lakes occurred during the 1960s and 1970s, when fish of consecutively younger ages were caught (Nümann 1972). Most of the studies of coregonid population dynamics claimed that anthropogenic eutrophication was the main cause of the acceleration in whitefish growth (Grimås et al 1972;Nümann 1972).…”

“…Most of the studies of coregonid population dynamics claimed that anthropogenic eutrophication was the main cause of the acceleration in whitefish growth (Grimås et al 1972;Nümann 1972). The decrease in whitefish growth from many European lakes towards the end of the 20th century was generally attributed to reoligotrophication (Kirchhofer 1995;Müller and Mbwenembo Bia 1998).…”

Some effects of eutrophication and the removal of aquatic plants by grass carp(Ctenopharyngodon idella)on rainbow trout(Salmo gairdnerii) in Lake Parkinson, New Zealand

“…Secondly, the effects of eutrophication on salmonids are frequently compounded by the presence or stocking of other fish species. Certain fish species, particularly cyprinids, are known to flourish in eutrophic lakes (Numann 1972;Le Cren et al 1972) and changed interactions between salmonids and these species could be a further factor in the decline of trout populations in some lakes. Furthermore, whereas changes in fish populations have been correlated with eutrophication, the causes of such (Larkin & Northcote 1969).…”

Étude de la production de préestivaux de corégone (Coregonus sp.) en cages éclairées immergées dans le Léman

“…1946;BATIAS, 1954;QUARTIER, 1954;CHRISTIE, 1963;NUHMANN, 1972et TODD, 1986) ont montré que les relâchers au stade "alevins vésicules " sont peu efficaces dans les grands lacs où il existe déjà un stock en place dont la reproduction naturelle est efficace. L'efficacité des relâchers d'alevins vésicules semble meilleure dans les petits lacs avec peu de prédateurs et sans corégones en place (CHAMPIGNEULLE, 1985) ou lorsque le relâcher peut être retardé par incubation des oeufs en eau froide (NUHMANN, 1972et LUCZYNSKI, 1984b ou à partir d'un seuil minimal de mise en charge (GERDEAUX et DEWAELE, 1986et TODD, 1986 Certains auteurs (EINSELE, 1965;VOLGIN, 1973 ;PRUKI ef a/., 1984 ;WESTMAN e/a/., 1984;LUCZYNSKI, 1986 ;MENG et al, 1986) indiquent des taux de recapture ou de survie de 2 à 80 % dans le cas de préestivaux ou d'estivaux de corégones contre seulement 0,1 à 4%o dans le cas des alevins vésiculés (ROTH, 1954;EINSELE, 1965;WESTMANNe/a/., 1984;LUCZYNSKI, 1986). Dans plusieurs pays, un effort accru a été porté lors des 15 dernières années sur les techniques de production de juvéniles de corégones soit en étangs (HOCHMAN et al, 1974;WESTMAN et al 1984;CHAMPI-GNEULE, 1985), soit en bassins avec du zooplancton vivant (GUNKEL et KAUSCH, 1979 ;STEFFENS, 1979;FLUCHTER, 1980) ou plus récemment de l'aliment sec (DABROWSKI et al.…”