The influence of riparian vegetation, woody debris, stream morphology and human activity on the use of rivers by southern river otters in Lontra provocax in Chile

Abstract

The distribution of the Endangered southern river otter Lontra provocax population in southern Chile has contracted, causing concern among otter specialists and conservationists. The main factor contributing to this decline is the loss of suitable habitat. Because the Chilean Irrigation Law promotes land drainage, the removal of riparian vegetation and canalization of lowland rivers in several provinces, this situation could deteriorate further. Using an Index of Revisitation Rate (IRR), we assessed the influence of woody debris, riparian vegetation, river bank morphology and river canalization on the use of rivers and streams by the southern river otter. Surveys were conducted on foot, on a monthly basis, between April 1999 and March 2001 in the south of Chile. The surveys covered 13 sections of rivers and streams, 3 km long and <50 m wide. River and stream banks with high density of riparian vegetation, woody debris and exposed roots had the highest IRR; most of the highly marked sprainting sites were found in this habitat. Canalized rivers and streams lacking these characteristics had the lowest IRR and hardly any highly marked sprainting sites. The data indicates that otters can tolerate some degree of riparian vegetation removal, provided there is minimum use of floodplains by humans. Temperate evergreen ombrophilus swamp forests and shallow watercourses with woody debris or gravel, riparian vegetation and a plentiful supply of macrocrustaceans appear to be the preferred habitat and conditions for the otter and may be key to its survival in freshwater habitats.