Selective predation by benthivorous fish on stream macroinvertebrates - The role of prey traits and prey abundance

The prey selectivity of fish depends largely on traits of the prey and the predator. Preferable prey traits might be different for visual predators (such as drift-feeding salmonids) and rather non-visual predators (such as benthic feeders). We evaluated the explanatory power of five prey traits and prey long-term abundance for the prey selection of small benthivorous fish by analysing the macroinvertebrate community and the diet of gudgeon (Gobio gobio) and stone loach (Barbatula barbatula) in two small submontane streams. Fuzzy principal component analyses, as well as electivity indices, revealed that the fish fed selectively. Prey size and feeding type were the most descriptive variables for the fish diet, followed by mean abundance, whereas microhabitat preference, locomotion mode and current velocity preference were less important. The fish preferred prey that was both small and consistently abundant, grazers and sediment feeders. Larger prey and shredders were avoided. The selection patterns of both fish species differed from those of visual fish predators but strongly resembled each other. Supporting this, in gudgeon which feeds slightly more visually than the strictly nocturnal stone loach, selectivity concerning prey traits as well as prey mean abundance was slightly more pronounced. We analyzed also selectivity for prey clusters based on the three most important variables. The observed selectivity patterns concerning these clusters were less pronounced but supported the other results. The maximum (neutral) electivity index was that of gudgeon for small, abundant grazers or sediment feeders, including chironomids. We conclude that prey selection of benthivorous fish that forage mainly non-visually can largely be explained by a small number of prey traits which probably work in combination. The prey preferences of these predators seem to be closely connected to their active foraging mode and to depend partly on the ability to detect prey visually. (C) 2015 Elsevier GmbH. All rights reserved.