In total, 298 transects (each 600 m long) were surveyed between 1987 and 1995 for otter Lutra lutra (Linnaeus, 1758) signs (spraints, smears and jellies) in nine rivers of NE Spain. Also two stretches of the rivers Noguera Ribagor^ana (length 2 km) and Noguera Pallaresa (length 2.6 km) in the Spanish Pyrenees were surveyed monthly between November 1989 and October 1990 for all otter tracks and signs. In both cases, all stones, rocks, beaches, hollows, caves, walls, shelves, and vegetation in the river and bankside within a 5 m band from the river edge (each side) were examined. The type of substrate on which findings were made was noted together with, the number of signs at a site. A seasonal pattern was found for the Pyrenean rivers with greatest sign density in winter and spring. In Mediterranean rivers, seasonality was not evident, founding even more signs in summer in some stretches. A total of 547.0 signs/km were recorded on the river Noguera Ribagor^ana during a year of study, of which 9.6% were smears, 1.0% jellies and 89.4% spraints. On the river Noguera Pallaresa 261.5 signs/km were noted, of which 9.2% were smears, 1.1% jellies and 89.7% spraints. A variation in sign deposition substrata (earth-beaches, grass, and rocks) and site (banks, middle river islands, caves/cracks, and river-stream confluences) throughout the year was observed, in the Noguera Ribagorfana stretch, periods of greatest sign deposition appear to be related to the presence of cubs. In accordance with the theory of the marking of resource use, a number of the spraints might not be significant, but rather the result of immature cub behaviour.
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