Size-related and diel variations in microhabitat use of three endangered small fishes in a Mediterranean coastal stream

Abstract

This study analysed the microhabitat use of three endangered fish species, Andalusian tooth- carp Aphanius baeticus, Iberian loach Cobitis paludica and sand smelt Atherina boyeri, in a coastal stream stretch. Plastic minnow traps were set both during daytime and at night on the bottom and at the surface. Depth and presence of effective refuge were recorded for each trap. To assess size-related changes in microhabitat use individuals of each species were classified in three size classes. The three species preferentially used bottom positions in the water column, though this behaviour was more evident in the case of Iberian loach. While large Iberian loach remained active at night Andalusian toothcarp and sand smelt were strongly diurnal, especially larger individuals. The three species showed a clear ontogenetic change in microhabitat pre- ferences towards deeper waters. Small Andalusian toothcarp and medium-sized Iberian loach used deeper microhabitat in the presence of refuge. Large Andalusian toothcarp consistently preferred exposed microhabitat at any time. Andalusian toothcarp using refuge were smaller at any time, while Iberian loach followed this pattern only at night. The differential vulnerability of these species to different predators (aerial and aquatic; diurnal and nocturnal) could explain the observed patterns in microhabitat use. Fish tended to co-occur in microhabitats either due to habitat characteristics independently of species or due to species independently of habitat. Andalusian toothcarp segregated spatio-temporally from sand smelt and Iberian loach, but these species occurred independently of each other. According to these co-occurrence patterns, Andalusian toothcarp would be more sensitive than Iberian loach or sand smelt to interspecific