within the two other temperature scenarios. Unfortunately,
it was not feasible within this study to track the
thermal histories of trout directly with implanted data
loggers or indirectly by ultrasonic telemetry. The overall
drop in estimated consumption is a consequence of the
reduced condition factor of the trout at the end of the period
studied in 2000 (R. J. RADKE, unpubl.). DAMSGARD
& LANGELAND (1994) found a similar effect in their
study and we agree with their assumption that the condition
factor of the stocked trout was well above normal
levels. With regard to the roach (approx. 110 kg ha -1, estimated
from the hydroacoustic survey) and trout
biomass (18 kg ha -1, according to stocked biomass in
spring 2000) the cumulative consumption of roach by
the trout would range from 2% (14 °C scenario) to 3%
(17 °C scenario) of total roach biomass in the period
studied during the first year of biomanipulation.
Based on the results of our study we suggest that the
trout were food limited during the summer period and
thus were forced to forage under the suboptimal thermal
conditions found in the epilimnic layer. Despite the
small amount of fish observed in the food of the trout we
think that the brown trout in the Saidenbach Reservoir
have the potential to be piscivorous to a much higher degree.