Home range and diet of re‐introduced European otters Lutra Lutra (L.) in Hertfordshire rivers

Abstract

The distribution and diet of two groups of captive‐bred, re‐introduced otters Lutra lutra (L.) was assessed through the collection and analysis of spraints (faeces), collected between July 1992 and March 1994 from the Rivers Stort, Lee and Rib in Hertfordshire (UK). Almost immediately after release in 1991, both groups of otters moved upstream of their release sites. In February 1992, one male was found dead on a road near the River Stort, and both groups appeared to have moved downstream, their total range eventually extending to about 40 km, from 8 km downstream of the confluence of the Rivers Stort and Lee to about 16 km up the Stort and 16 km up the Lee. Fish, principally cyprinids, formed the major dietary element, with spatial differences in prey availability influencing the range of secondary items taken. Eels were the only prey category to show significant seasonal variation in spraints, occurring more often than expected in spring and summer spraints. Mammals/amphibia and birds were taken as prey only occasionally. Where environmental quality and/or prey species diversity were low, small‐bodied fish species, such as three‐spined stickleback Gasterosteus aculeatus, bullhead Cottus gobio and stone loach Barbatula barbatula, occurred more frequently in the diet. Only two of the seven IUCN criteria for re‐introductions appear to have been met before the otters' release, and subsequent assessments suggest that most other criteria were not. As there has been only one possible, but unconfirmed, sighting of a female with cubs, it remains unclear whether the released otters have reproduced and thus the success of the re‐introduction is doubtful. Copyright © 1995 John Wiley & Sons, Ltd