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

25 The prey selectivity of fish depends largely on traits of prey and predator. Preferable prey 26 traits might be different for visual predators (such as drift-feeding salmonids) and rather non27 visual predators (such as benthic feeders). We evaluated the explanatory power of five prey 28 traits and prey long-term abundance for the prey selection of small benthivorous fish by 29 analysing the macroinvertebrate community and the diet of gudgeon (Gobio gobio) and stone 30 loach (Barbatula barbatula) in two small submontane streams. Fuzzy Principal Component 31 Analyses, as well as electivity indices, revealed that the fish fed selectively. Prey size and 32 feeding type were the most descriptive variables for the fish diet, followed by mean 33 abundance, whereas microhabitat preference, locomotion mode and current velocity 34 preference were less important. The fish preferred prey that was both small and consistently 35 abundant, grazers and sediment feeders. Larger prey and shredders were avoided. The 36 selection patterns of both fish species differed from those of visual fish predators but strongly 37 resembled each other. Supporting this, in gudgeon which feeds slightly more visually than the 38 strictly nocturnal stone loach, selectivity concerning prey traits as well as prey mean 39 abundance was slightly more pronounced. We analysed also selectivity for prey clusters based 40 on the three most important variables. The observed selectivity patterns concerning these 41 clusters were less pronounc d but supported the other results. The maximum (neutral) 42 electivity index was that of gudgeon for small, abundant grazers or sediment feeders, 43 including chironomids. 44 We conclude that prey selection of benthivorous fish that forage mainly non-visually can 45 largely be explained by a small number of prey traits which probably work in combination. 46 The prey preferences of these predators seem to be closely connected to their active foraging 47 mode and to depend partly on the ability to detect prey visually. 48 49