Groyne-heads as potential summer habitats for juvenile rheophilic fishes in the Lower Oder, Germany

Abstract

The present study aims to test the hypothesis that artificial structures, the riverward ends of groynes or groyne-heads, function as potential habitats for young rheophilic fish. The investigation was undertaken in summer 1998 on the River Oder, in the Polish-German National Park ‘Lower Oder Valley’, eastern Germany. Fish were caught on groyne-heads using point abundance sampling by electrofishing and compared with specimens collected by the same method in seven additional mesohabitats (navigable side-canal, sandy river bank, riprap, deep groyne, sandy groyne, connected backwater, polder waterbody). Groyne-heads were inhabited by bottom-oriented 0+ rheophilic stone loach Barbatula barbatula (L.) and burbot Lota lota (L.), whereas 0+ rheophilic cyprinid fish were more abundant in shallow-sloped, sandy shoreline mesohabitats. Of all sites investigated, 1+ juveniles were most abundant on groyne-heads, in which the rheophilic group formed a large proportion of the total catch. From our results we conclude that groyne-heads constitute an important habitat for both 0+ and 1+ juvenile rheophilic fish during summer-time, but that its use is limited by the stochastic availability due to varying discharges.