Is Switzerland with its abundance of water a paradise for fish-eating birds?
Switzerland’s lakes and rivers provide suitable habitat for fish-eaters. Distribution and abun-dance of most larger species have shown a positive trend since 1993–1996, but this could soon change as birds once again face persecution.
Fish-eating birds were heavily persecuted well into the 20th century. As late as 1931 the federal government and the cantons paid a two-franc bounty for each Great Crested Grebe killed. Dividing birds into useful and harmful species gradually gave way to the recognition that all species have their niche in the ecological system. Scientific studies have shown that predators rarely control prey populations, but that in fact the opposite is true. Persecution abated thanks to this realisation. Close seasons were introduced, certain species placed under protection, like the Grey Heron in 1926, and no-hunting zones established, leading to a trend reversal. The protection of breeding colonies at a European level was critical for the renewed spread of the Great Cormorant.
Changes in water quality also played a part. Most Swiss lakes are naturally oligotrophic, meaning that they have low levels of nutrients. From the 1950s, an increase of phosphorus input from wastewater and nutrient input from fertilised farmland caused changes in fish fauna. Stocks of cyprinids (carp family) and perch increased. Fish species such as whitefish Coregonus sp., which typically occur in deep, oligotrophic lakes, would have disappeared in many places without artificial stocking. Initially, the Great Crested Grebe may have benefited from the increased supply of cyprinids, at least on some lakes, but only to a certain extent. In very nutrient-rich (eutrophic) waterbodies, excessive algal growth led to reduced water transparency and especially to oxygen depletion, affecting the reproduction of fish. In extreme cases such as Lake Sempach LU this led to the collapse of fish stocks followed by the collapse of the Great Crested Grebe population. Both populations only recovered once water quality improved thanks to reduced nutrient input, especially phosphorus.
In general, the lakes and rivers of Switzerland are attractive for fish-eating birds. The three largest lakes, Lakes Geneva, Constance and Neuchâtel, support three quarters of all Great Cormorant pairs and about half of all Great Crested Grebes, but only about 30 % of Goosanders; the latter also frequently breed along rivers. Since Switzerland accommodates a large proportion of the European population of Great Crested Grebes and Goosanders, which form a separate Alpine population, our country has an international responsibility for these species.
Unfortunately, fish-eating birds are again being seen as competitors and pests by hobby anglers and fisheries. However, the real threats to fish stocks are water control structures, hydropower stations and pesticides. Pressure from the fishery sector led to 46 Grey Herons and 19 Goosanders being shot on average per year in 2013–2016. These protected species were killed – a maximum of 96 Goosanders in 2007 and 212 Grey Herons in 2003 – without sufficient evidence of damage. Great Cormorants and Great Crested Grebes are only protected in certain cantons. At 103 individuals per year (average 2013–2016) the size of the hunting bag for the Great Crested Grebe is small compared to that of the Great Cormorant at 1313 individuals. Should the persecution of fish-eating birds intensify, an adverse effect on local populations cannot be excluded.
Escher, M. & P. Vonlanthen (2005): Entwicklung der Gänsesäger in der Schweiz (im Vergleich zu Graureiher und Kormoran). Aqua-Sana, Ulmiz.
Fischnetz (2004a): Dem Fischrückgang auf der Spur. Schlussbericht des Projekts "Netzwerk Fischrückgang Schweiz". Eidgenössische Anstalt für Wasserversorgung, Abwasserreinigung und Gewässerschutz (EAWAG), Dübendorf.
Fischnetz (2004b): Sur la trace du déclin piscicole. Rapport final du projet "Réseau suisse poissons en diminution". Institut fédéral pour l’aménagement, l’épuration et la protection des eaux (IFAEPE/EAWAG), Dübendorf.
Hänni, E. (1932): Haubentaucher-Abschuss 1931 in St. Gallen. Ornithol.Beob. 30: 27.
Hefti-Gautschi, B., M. Pfunder, L. Jenni, V. Keller & H. Ellegren (2009): Identification of conservation units in the European Mergus merganser based on nuclear and mitochondrial DNA markers. Conserv. Genet. 10: 87–99.
Keller, V. (2009): The Goosander Mergus merganser population breeding in the Alps and its connections to the rest of Europe. Wildfowl Special Issue 2: 60–73.
Keller, V. (2015): Haubentaucher und Co: Reaktionen auf die Veränderungen der Wasserqualität am Sempachersee. Vogelwarte 53: 426.
Keller, V., R. Ayé, W. Müller, R. Spaar & N. Zbinden (2010): Die prioritären Vogelarten der Schweiz: Revision 2010. Ornithol. Beob. 107: 265–285.
van Eerden, M. R. & J. Gregersen (1995): Long-term changes in the northwest European population of Cormorants Phalacrocorax carbo sinensis. Ardea 83: 61–79.