The Eurasian otter (Lutra lutra) in the network of small steppe rivers of the Northern Black Sea region

Abstract

The Lower Bug region is the habitat of the Eurasian otter (Lutra lutra¬), which, relying on channel reservoirs as reserves, also exploits the seasonal and permanent resources of small steppe rivers. With the climate-driven decrease in surface runoff, small rivers have become subject to complete or partial drying up, making it difficult for semi-aquatic mammals to live. The survival of the otter in the Southern Steppe is ensured by its use of the static and foraging potential of channel reservoirs and ponds. The latter are the key sites that serve as permanent and off-season reserves for the species, ensuring the survival and sustainable existence of otters in the small river network. The habitat specificity of the otter's sustainable habitats covers areas with different spatial and landscape characteristics, and hydrological, and foraging features, which allows us to distinguish three ecologically and ethologically distinct forms of the species. The first is the primary riverine form, represented by animals inhabiting the Southern Bug, Syniukha, and Ingul rivers, the second is the lyman-estuarine form, and the third is the river-pond form associated with small rivers. The current number of otters in the Lower Pobuzhzhia is estimated at 86–108 individuals, which is 38.5% more than in 2000–2005 and 58.1% more than in 1992–1995. The average breeding density is 0.489 individuals/10 ha of water area (excluding the coastal and marine zone). In some habitats, the local density of otters ranges from 0.181 (Berezansky estuary) to 1.14 individuals/10 ha (lower reaches of the Syniukha River, Kovalivsky plains). At the same time, the main reserves of the species generally remain unchanged—the channel-floodplain habitats of the Southern Bug, Ingul, and Ingulets, from which the animals disperse to the tributaries of these rivers and adult males migrate through local watersheds. Some small otter habitats are associated with the peaks and banks of the Tiligul and Berezan estuaries. The least studied was and remains the Ingulets centre of existence of the species, which was significantly affected by the consequences of hostilities.