| Summary: | The aim of the present study was to analyse and compare the feeding behaviour of large eels Anguilla anguilla (> 30 cm total length) in two lakes of different environmental state and corresponding differences in food availability. Investigations were conducted in Lake Großer Vätersee, Germany (clear water, mesotrophic, submerged macrophytes present) and in Lake Vallum, Denmark (turbid, eutrophic, no submerged macrophytes). Fish were sampled regularly by electrofishing. We focused our study on diet patterns. The availability of macrozoobenthos was higher in Lake Vallum (3,500 ind. m-2) than in Lake Großer Vätersee (1,500 ind. m-2), which was due to a high density of insect larvae in Lake Vallum (2,700 ind. m-2) compared to Lake Großer Vätersee (680 ind. m-2). Both, the abundance of eels and small prey fish (40-99 mm TL) were higher in Lake Vallum. Despite the latter, fish was unimportant as prey for eels in Lake Vallum which instead fed on macroinvertebrates and in particular chironomid larvae. In contrast, in Lake Großer Vätersee where availability of insect larvae was low eels used fish as the main food component. Based on these results as well as similar observations for smaller eels, we suggest that piscivory among eels to a wide extent is generally controlled by the availability of insect larvae. Stable isotope analyses confirmed the dietary results. The estimated mean trophic positions of eels in Lake Großer Vätersee (3.74 ± 0.2) was one level higher than those of eels in Lake Vallum (2.71 ± 0.2). Stable isotopes provided an estimate of 82% benthic reliance in the carbon signature of eels in Lake Vallum and 37% in Lake Großer Vätersee, indicating that eels may act as integrators between benthic and pelagic food webs when availability of insect larvae is low. JRC.G.3 - Agriculture
|
|---|