An evaluation of the habitat used by otters (Lutra lutra) in Lancashire as a reference for habitat creation at a newly acquired Wildlife Trust site.

Abstract

A study was undertaken to determine the environmental variables of water quality,
habitat quality and fish availability and their relationship with otter presence. The study,
located on the Ribble catchment in Lancashire, was completed during the summer
months of July, August and September 2007. The locations of otter occurrence or
absence were determined with the use of recent Environment Agency otter survey
records. Locations of otter prevalence and absence were surveyed to establish any
inherent differences. The data obtained was subsequently used to recommend riparian
habitat enhancements specifically for otters at a newly acquired Wildlife Trust site
situated on the River Ribble.
Fish densities were greater at sites with known otter activity. Juvenile trout and salmon
were absent or low at sites with no otter activity. The water quality survey revealed
nitrate content to be at least 3 times higher in concentration on the sites with otter
absence. High nitrate concentrations may be impacting certain fish species and fish
densities at these sites and may explain otter absence. Mature bank-side trees and tree
roots were associated with otter presence. Habitat parameters such as bank-side fences,
bank-side paths and associated criteria were established to have impacts on otter
occurrence. All environmental variables have to be considered to provide a definitive
answer to the condition of a watercourse in relation to otter colonisation.