The effects of riparian habitat quality and biological water quality on the European Otter (Lutra lutra) in Devon

Abstract

After a period of decline, European Otter (Lutra lutra) populations are showing signs of recovery throughout the UK. Populations in Devon are thought to be almost fully recovered, although exact numbers are unknown; however, there are still rivers within Devon that do not appear to support Otter populations. The aim of this research was to determine the relationship between environmental condition and the presence of Otters by comparing the quality of riparian habitat of rivers with and without evidence of Otters. The research was undertaken in four rivers in Devon, the Rivers Culm, Ken, Coly and Otter: the first two being river stretches with no documented evidence of Otter populations, and the latter two having documented evidence of Otter populations. Along each of the rivers, 10 sections of 50 m were sampled. In each section, the riparian habitat quality was recorded using the Qualitat del Bosc de Riberia index. The biological water quality was determined by calculating Biological Monitoring Water Party scores, and water chemical concentrations were obtained from Environment Agency data. The riparian habitat quality and biological water quality were found to be of significantly lower quality in the river stretches that did not have evidence of Otter populations when compared with those with Otter populations. The chemical water quality was correlated to biological water quality: the quality being worse in the rivers without evidence of Otter populations. The results of this research suggest that rivers with no evidence of Otter populations are generally of worse riparian quality than those supporting Otter populations.