
Freshwater Crayfish 12(1): 943-944 (1999)
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Astacus leptodactylus - a threat to native crayfish species in Lake Aegeri, Switzerland
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Abstract
Lake Aegeri hosts three crayfish species: Austropotamobius torrentium, Astacus astacus and Astacus leptodactylus. The latter species, originally from Eastern Europe, was caught for the first time in Switzerland in 1979. It has a higher reproductive rate and grows faster than the other two species, which are indigenous to Swiss waters. To estimate the potential of Astacus leptodactylus to threaten the two indigenous species in Lake Aegeri, I examined by SCUBA-diving the distribution and relative densities (CPUE = catch per unit effort = No. of crayfish per man hour) of species in the lake, their association with different substrate types as well as the physical and ecological state of the three populations. I found crayfish at 29 of 32 sites near the shore between April and September 1997. I found only one species at 7 sites, two species at 16 sites and all three species at 6 sites. The highest local densities observed were 61 CPUE for Astacus leptodactylus, 35.5 CPUE for Astacus astacus and 20 CPUE for Austropotamobius torrentium. The three species were found at 22, 15 and 19 sites, respectively. Austropotamobius torrentium seems to prefer a stony substrate, while the two Astacus species, especially Astacus astacus were more often found at sites with a muddy substrate and reed vegetation. Reproduction was found in all three species and none of the populations were overaged. Limb loss frequency in both Astacus species was higher where Astacus leptodactylus was present at high densities. There is no evidence yet to prove the ousting of indigenous species by Astacus leptodactylus in Lake Aegeri. Further sampling is being performed in Lake Aegeri by our group.
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Romer J. (1999). Astacus leptodactylus - a threat to native crayfish species in Lake Aegeri, Switzerland. Freshwater Crayfish 12(1):943-944. doi:
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