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Abstract

The feeding ecology of three piscivorous fish species; perch (Perca fluviatilis), pike (Esox lucius) and burbot (Lota lota), was studied in the subarctic Pasvik watercourse (69 o N), northern Norway and Russia. All three species primarily occupied the benthic habitats in the watercourse. Perch and burbot exhibited distinct ontogenetic niche shifts in food resource use; perch changing from a dominance of zooplankton to zoobenthos to fish, and burbot from zoobenthos to fish. Fish prey dominated the diet of all the investigated size-classes of pike, but small-sized pike (<20 cm) were not represented in the sample. Fish prey size was positively related to predator size in all three species. Whitefish (Coregonus lavaretus) was the dominant prey of pike and large-sized burbot and perch. Nine-spined sticklebacks (Pungitius pungitius) was also an important prey and appeared to be a dietary stepping-stone enhancing the transition from invertebrate feeding to consumption of large-sized whitefish prey for all three predators. A cluster analysis separated the different size groups of the three predator species into five functional feeding groups, most of them containing two or all three species. Within these feeding groups, and especially among the piscivorous size-classes, there was a strong and significant interspecific overlap in prey selection, and the dietary similarities between the species were in general much larger than the intraspecific similarities between ontogenetic stages. All three piscivorous species are important top predators in the aquatic food web of the watercourse, and their ontogenetic diet shifts and resource partitioning patterns generate a substantial food web complexity in this subarctic ecosystem.

Ontogenetic Dietary Shifts and Food Selection of Endemic <I>Squalius Carolitertii</I> (Actinopterygii: Cypriniformes: Cyprinidae) in River Tormes, Central Spain, in Summer

“…These shifts during life stage transitions may be accompanied by a marked reduction in intraspecific competition within the fish population, facilitating the partitioning of resources (Elliott 1967, Amundsen et al 2003, Oscoz et al 2006. In the present study, agerelated shifts in the diet of S. carolitertii occurred at three different levels.…”

Ontogenetic Dietary Shifts in a Predatory Freshwater Fish Species: The Brown Trout as an Example of a Dynamic Fish Species

“…These shifts during fish life stage transitions may be accompanied by a marked reduction in intra-specific competition in the fish population, facilitating the partitioning of resources [e.g. 45,46]. Moreover, dietary analyses usually show high values of diet overlap among age classes, but the differences in the use of feeding habitat and behavioural feeding habits are important adaptive features that may reduce the intra-specific competition in the population [23].…”

Stable isotopes and gut contents indicate differential resource use by coexisting asp (Leuciscus aspius) and pikeperch (Sander lucioperca)

“…Ontogenetic variations in the resource use among potential competitors have been examined less frequently (Amundsen et al, 2003;Davis, Blanchette, Pusey, Jardine, & Pearson, 2012;Werner & Gilliam, 1984) although this knowledge is important to fully understand the structure and functioning of fish communities.…”