Hydraulic microdistribution patterns of larval fire salamanders (Salamandra salamandra salamandra) in the Weidlingbach near Vienna, Austria

1. This study examined the longitudinal distribution of larval fire salaman ders (Salamandra salamandra salamandra L.) in the Weidlingbach system, a fi rst- to fourth-order tributary of the Danube near Vienna, Austria. On the m icrohabitat scale, actual current velocities, Reynolds numbers and Froude n umbers at larval locations were measured and larval positions mapped. 2. Larval densities were highest in shallow first- and second-order tributa ries where mean current speeds were less than 20 cm s(-1), mean Reynolds nu mbers were less than 12 000 and mean Froude numbers were less than 0.30. Yo ung larvae appeared on 26 April, fully grown larvae were observed from 11 M ay and larvae started metamorphosis from 27 June. Young adults left the bro ok between 26 August and 8 September. A severe flood on 25 May significantl y reduced larval density, especially at sites near the source. 3. At a given sampling station young larvae favoured microhabitats exposed to only minor hydraulic stress. As larvae grew, they also colonized microha bitats with moderate current velocity (4-15 cm s(-1)). At sites with genera lly low discharge, larvae were distributed over a wider range of current ve locities than at sites with higher discharge; at the latter, larvae were co nstricted to sheltered microhabitats.