The Caucasian Dwarf Goby (Knipowitschia caucasica)—Population Dynamics and Feeding Ecology in the Lower Rhine With a Special Focus on Winter

Abstract

Artificial expansion of shipping routes in the course of international trade opens up fish migration routes for numerous species. Since 2006 migration of four different goby species took place from the Ponto–Caspian region to the Lower Rhine. Neogobius fluviatilis, Neogobius melanostomus, Proterorhinus semilunaris and Ponticola kessleri were able to establish in the local fish community of the Lower Rhine. Besides the four other goby species, Knipowitschia caucasica migrated from the Ponto–Caspian region to the Lower Rhine as well in 2019. Due to increasing abundance in the last years and lack of information regarding population dynamics, feeding activity and prey preferences of the dwarf goby, the length of 1218 Caucasian dwarf gobies was analysed as well as the diet of 519 individuals in the course of May 2021 to February 2022. The populations of three different locations along the Lower Rhine were examined in winter on differences in population dynamics and feeding ecology. Analysis of the population over time suggests that K. caucasica in the Lower Rhine is an annual species with spawning during summer. The juvenile individuals of the Caucasian dwarf goby increased in total length until winter, while the adults vanished after spawning. Both juveniles and adults mainly fed on zooplankton and insect larvae. The feeding activity of the dwarf goby was higher in summer than in winter and started to increase as early as February. No difference in winter prey was recorded between populations at different sites, as all populations fed mostly on copepods and chironomids.