Diet Niche Relationships among Early Life Stages of Fish in German Estuaries.

Diet composition, selectivity, food niche width and food niche overlap of early life stages of fishes were studied in the Barther Bodden system and in the Weser and Elbe estuaries during spring and summer from 1987 to 1991 and from 1993 to 1994. Larvae of perch (Perca fluviatilis) and roach (Rutilus rutilus) dominated in the Barther Bodden. Herring (Clupea harengus) and perch were the dominant species in the Barther Strom. Smelt (Osmerus eperlanus) was the most common species in the Elbe estuary. Sprat (Sprattus sprattus) was of most importance in the Weser estuary. The dominant prey of fish larvae were copepodids, nauplii and eggs of Eurytemora afinis. The highest food niche width was observed for nine-spined stickleback (Pungitius pungitius), ruffe (Gymnocephalus cernuus), three-spined stickleback (Gasterosteus aculeatus) and perch in the Barther Bodden. Negative selectivity indices indicated that populations of rotifers were scarcely influenced by predation by fish larvae. In contrast, E. affinis was preferred by early life stages of fish. Positive relationships were estimated between maximum prey lengths and predator lengths of different fish species. Key species with regard to niche overlap were nine-spined stickleback, roach, three-spined stickleback and perch in the Barther Bodden, perch and herring in the Barther Strom, herring and three-spined stickleback in the Elbe estuary, and sprat and common goby (Pomatoschisrus microps) in the Weser estuary. High geographical overlap between fish species occurred in the Elbe estuary and Barther Bodden, whereas high diet overlap was estimated for both the Weser estuary and Barther Strom.