Rapport nr 143: Förekomst av kräfta i fyra sjöar i Geta, norra Åland 2015
GRIPENBERG, F (2015)
GRIPENBERG, F
Åbo Akademi, Husö biologiska station
2015
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Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-12-3317-3
https://urn.fi/URN:ISBN:978-952-12-3317-3
Tiivistelmä
In the summer of 2015 a study was conducted concerning the status (amounts and species) of crayfish populations in four lakes in Geta, northern Åland. The studied lakes were Lake Byträsk, Lake Norsträsk, Lake Gröndals träsk and Lake Olofsnäs träsk. The lakes have previously been studied by SUNDBLOM (1964) and STORBERG (1980). The usage of the noble crayfish (Astacus astacus) has long traditions in the Nordic countries, and is considered to have a high cultural and economic significance. As a response to the declining crayfish populations during the 20th century the American signal crayfish (Pacifastacus leniusculus) was introduced, and with it the for A. astacus deadly, crayfish plague. Crayfish plague and overfishing are the two largest threats to local crayfish populations. The sampling as conducted during the legal crayfishing period on the Åland slands
(20.7-31.8) with 20 overnight crayfish traps during 3 separate nights. The crayfish population in Lake Byträsk was the most viable on Åland during the 1960s, with annual catches close to 20000 individuals. During the 1970s the catches had decreased to 5000-7000 individuals and in 2015; 31 individuals were caught. In Lake Norsträsk the annual catches during the 1960s and 1970s were around 3000-4000 individuals. During 2015; 349 individuals were caught. In Lake Gröndals träsk the previously noted catches were around 1500-2000 individuals annually. During the 2015 sampling 117 individuals were caught. The crayfish from Lake Gröndals träsk had the mallest mean length. In Lake Olofsnäs träsk the catches had decreased rom 8000 during the 1960s to 500-800 during the 1970s. During 2015 a otal of 202 crayfish were caught. The crayfish from Lake Olofsnäs träsk had the highest mean length.
(20.7-31.8) with 20 overnight crayfish traps during 3 separate nights. The crayfish population in Lake Byträsk was the most viable on Åland during the 1960s, with annual catches close to 20000 individuals. During the 1970s the catches had decreased to 5000-7000 individuals and in 2015; 31 individuals were caught. In Lake Norsträsk the annual catches during the 1960s and 1970s were around 3000-4000 individuals. During 2015; 349 individuals were caught. In Lake Gröndals träsk the previously noted catches were around 1500-2000 individuals annually. During the 2015 sampling 117 individuals were caught. The crayfish from Lake Gröndals träsk had the mallest mean length. In Lake Olofsnäs träsk the catches had decreased rom 8000 during the 1960s to 500-800 during the 1970s. During 2015 a otal of 202 crayfish were caught. The crayfish from Lake Olofsnäs träsk had the highest mean length.