Abstract

Consecutive surveys of otter spraints of both banks along a 28-km stretch of the River San showed an average of 4.18 deposited spraints/km per day during a 3-week pre-experimental period. The variation in spraint density on particular 1-km-long sections of the river was high and varied from 40 to 145 spraints/km after 3 weeks. Spraint deposition was positively correlated with the proportion of steep and rocky riverbanks, which were characterised by a higher number of potential sprainting sites than those with many flat and undermined banks. Average daily deposition of spraints on the whole 28-km stretch after experimental removal of spraints (experimental period) did not significantly differ compared to the pre-experimental period. However, in sections where otter spraints were removed (n=14), sprainting intensity increased 1.6-fold, while in the control sections (n=14) the defecation ratio decreased 1.5-fold during the first week after removal. Placement of additional spraints of unfamiliar individuals on half the experimental sections did not stimulate otters to increase defecation on these sections compared to those where only old spraints were removed. Otter response to the removal of spraints has a spatial character and is expressed by differentiation in spraint deposition within the home range.