The Goosander as potential indicator of naturalness and biodiversity in submontane river valleys of northern Carpathians

•A holistic ecological indicator for submontane rivers is proposed.•Relations between Goosander occurrence, environmental variables and biodiversity indices are analyzed.•Goosanders were shown to be associated with a high naturalness of valleys, but not with hydrogeomorphology and urbanization.•The studied species’ distribution is correlated with high aquatic animal richness and allows for a high prediction accuracy of some species (e.g. Natura 2000).•Goosanders could be used as an excellent indicator and umbrella/flagship species in submontane valleys in northern part of the Carpathians.

Riparian habitats are biodiversity hotspots, however, despite their protection (e.g. in Natura 2000 sites) they are drastically transformed, particularly in more developed countries. The least inventoried, monitored and protected are submontane drainages composed of lowland and mountain habitats and species. Effective evaluation and monitoring of riparian habitat quality and species richness in submontane valleys is difficult and time consuming, but could be overcome by using indicator species. In this work, we verify if Goosander Mergus merganser could be considered as indicators of submontane valleys’ naturalness and biodiversity. Data about Goosander occurrence in the Raba drainage (Polish Carpathians) were compared with several environmental variables and information about species richness of selected riparian animals. Goosander distribution and abundance depended on “naturalness” variables (high share of alluvia and scarps in river channels and forests on river banks), but association with hydrogeomorphology and the vicinity of humans was not found. Goosander abundance was found to be significantly correlated with bird species richness (both forest- and river-dwellers) and the presence of aquatic mammals (beavers and otters), but not with a richness of fish. Moreover, Goosander allows a high prediction accuracy to be achieved for the presence of aquatic animals (otters, beavers, woodpeckers and river-dwelling birds), among others, species annexed in EU directives. The correlation of Goosander abundance with the richness of riparian vertebrates, as well as with natural riparian habitats makes this bird a good candidate for an umbrella and flagship species. Moreover, using Goosanders as indicators would be a valuable method for preliminary valorization and further monitoring of habitats and species in Natura 2000 sites of Polish Carpathians. The utility of this species as bioindicator in other parts of the Carpathians should be verified after saturation of available areas by its populations.

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