Abstract

In the early decades of this century the rivers and streams in the vicinity of Heidelberg were populated by two crayfish species, the noble crayfish Astacus astacus and the stone crayfish Austropotamobius torrentium. A. astacus inhabited the River Neckar (altitude: 105 m) and probably also larger lowland tributaries, and A. torrentium occupied the streams and brooks of the low mountain ranges Odenwald and Königstuhl. Nowadays, we have three crayfish species, A. torrentium and the American Orconectes limosus and Pacifastacus leniusculus. Several populations of A. torrentium are still present in the Odenwald at an altitude of 180–400 m. One of these populations lives sympatrically with deliberately released O. limosus. In the Königstuhl area the stone crayfish has disappeared. O. limosus was first recorded in the region of Heidelberg in 1956. It has invaded the Neckar via the River Rhine and has migrated approximately 100 km upstream since then. Interestingly, in 1956 A. astacus was still present in the Neckar and coexisted with O. limosus but disappeared later on. O. limosus is now widely distributed in the Rhine and Neckar, and in gravel pits of the Rhine Valley. P. leniusculus has erroneously been introduced as noble crayfish into the Lobbach, a tributary of the Elsenz which flows into the Neckar near Heidelberg. Approximately 400 crayfish were released 9 years ago. By recapture experiments the present population has been estimated at 40,000 individuals. In the last years, P. leniusculus has spread down the Elsenz and is now close to the confluence with the Neckar. From our three crayfish species only P. leniusculus is exploited by local fishermen.

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