Structure of an otter (Lutra lutra) population in Germany – results of DNA and hormone analyses from faecal samples

Population size, one of the basic biological parameters is particularly difficult to estimate for nocturnal animals with cryptic life style and little individual distinctiveness like Eurasian otters (Lutra lutra). Because telemetric methods often fail and also expose the animals to a high risk of injuries and even mortality, we analysed DNA and hormones of spraints to obtain data on population density and structure of free-living otters in a Nature Park in north-eastern Germany. We were able to assign 53 different individual profiles from faecal samples and obtained six more profiles from animals found dead inside the park. The total population estimate (n=59) consisted of at least 32 males and 27 females; 33 animals were adult, 23 younger than 2 years (three of unknown age). Marking points were frequented by up to 12 individuals. Estimated density was one animal per 4.7 km of shoreline. The genotypically estimated total population size was more than 2.5 times as high as estimated in the past census. The method was also suited to compare otter population densities in different areas or at different times in the same area.