Hydromorphology meets mammal ecology: morphological quality index, recent channel adjustments and otter resilience

The need for a multidisciplinary approach for characterizing water bodies in terms of morphological, chemical and ecological quality has hastened the growth of hydromorphology as a cross-disciplinary topic at the interface of hydrology, geomorphology and ecology. Many authors have analysed how hydroecology may affect freshwater biodiversity, although little is known about how this biodiversity might be affected by river morphological quality. We examined how well the presence of the semi-aquatic Eurasian otter can be predicted by the rivers’ morphological quality and its adjustments over the last decades. We tested the morphological quality index (MQI) methodology in 38 reaches of five rivers in southern Italy, 23 of which were positive to otter presence. In each reach, we examined 28 indicators contributing to the MQI and its 11 sub-indices. The results showed a significant relationship between the probability of the presence of otters, MQI, and some sub-indices. The best performing sub-indices were related to channel adjustments and the continuity of river processes. A more detailed analysis of channel adjustments showed a detrimental effect of channel incision (>3m) and a positive effect of narrowing, particularly where it occurred simultaneously with the development of forest in the new floodplain. The continuity of river processes has driven the migration of river banks and the development of ponds and secondary channels, likely increasing the availability of dens and resting sites and the hunting capabilities of otters. Our results stressed the importance of fluvial dynamics and sustainable adaptive river management for the habitat quality of semi-aquatic species.