Mortality patterns of otters (Lutra lutra) from eastern Germany

Abstract

Data obtained from the dissection of 1067 otters Lutra lutra were used to compare the causes of mortality in relation to age composition, time trends, and regions. Age determination was based on the analysis of incremental cementum lines in teeth. Major causes of mortality of otters were traffic accidents (69.9%), followed by natural deaths (6.6%), deaths in fish-traps (6%), hunting (4.1%), and other violent events (4.4%). No significant differences in mortality structure between the sexes were found. Resulting from a log-linear and a contrast analysis, significant differences in frequencies of mortality causes in relation to different time periods, regions and age classes of otters were observed. The frequency of otters dying from hunting or diseases was highest in youngest (AC I) and oldest (AC V) otters. Generally, the greatest differences between age classes resulted from comparison of frequencies of traffic-mortality, hunting, and fish-traps. Concerning time trends, the greatest differences were found in the periods before and after 1990. In addition to the increase of traffic-mortality, hunting and deaths in fish-traps influenced the distribution of mortality in different time periods. In eastern Germany, there is a clear difference in mortality between northern and southern regions. This results mainly from commercial fish-trapping being more common at the northern coast and lakes. However, in all different subsamples of time, region or age-class, traffic-killed otters amounted to >50% of all otters found dead.