Pathological Findings in Eurasian Otters (Lutra lutra) Found Dead between 2015−2020 in Schleswig-Holstein, Germany

Abstract

In times of massive biodiversity loss and ongoing environmental crises, it is extremely important to ensure long-term conservation efforts of threatened species like Eurasian otters (Lutra lutra). To gain insights into the status of Northern Germany’s otter population, 92 otters found dead in Schleswig-Holstein between 2015−2020 were collected and underwent detailed dissection with the aim to establish a monitoring program for this population. Examinations followed a protocol especially designed for otters, including various biological data assessments and extended sampling. The finding sites showed a clear concentration in the Continental region. Seasonal concentration differed among the years, yet peaks were seen from fall to winter. Overall, more males than females were found, although this differed among the years. The majority of otters that could be aged were between 1–3 years. Placental scars and pregnancy were recorded in only few females. Nutritional status was good in most cases. Infectious diseases found included Vagococcus lutrae, Toxoplasma gondii, and Emmonsia spp. A major cause of death was roadkill. Known sample bias in studies focusing on roadkill was considered in the finding interpretation. Continuation of the population health investigations is mandatory to analyze potential trends and to establish an actual monitoring program for Eurasian otters in Schleswig-Holstein.

Health and Mortality Monitoring in Threatened Mammals: A First Post Mortem Study of Otters (Lutra lutra L.) in Italy

“…ticks (1–3) per individual, although the detachment of ticks shortly after death cannot be excluded. Prevalence (10%) was similar to that reported in German populations [ 42 , 50 ] but lower than in the UK [ 48 ]. The role of otters in the dispersal of tick-borne pathogens and in the maintenance of their sylvatic cycles is still unknown [ 51 ], but probably negligible due to habitat specialization and continuous contact with water.…”

“…Road mortality showed a seasonal pattern with most otter road-kills occurring during autumn and winter. A similar pattern has been recorded in other otter PM studies [ 15 , 17 , 42 , 70 , 72 ] and has been related to heavy rains and floods occurring in autumn–winter, making swimming through culverts difficult for otters [ 15 , 72 ]. It has been also hypothesized that otters are more vulnerable to road casualties during autumn–winter, because the darkness is prolonged and a large overlap between otter and human activities, including driving, occurs [ 17 , 72 ].…”

“…Three otters died from natural causes (11%). Other studies in Central and northern Europe reported similar or lower percentages of recorded natural deaths [ 29 , 41 , 42 ]. Obviously, causes of natural mortality detected in submitted death otters do not reflect the rate of natural mortality in Eurasian otter populations (an otter dying from natural causes far away from roads is rarely detected).…”

“…The age distribution of submitted otters was skewed towards younger individuals in both sexes. A left-skewed age structure was commonly reported in PM studies of otters across Europe [ 39 , 40 , 41 , 42 ] (but see [ 30 ], where the majority of road-killed otters were aged individuals). Young individuals are less experienced and more prone to die due to traffic collision.…”

“…However, road-killed otters were mostly 1–2-year-old males in our cases. A male bias in road fatalities has been extensively reported in otter and mustelids studies [ 41 , 42 , 72 , 74 ], and it could be a consequence of larger home ranges, higher energetic requirements, or long distance traveled [ 37 , 41 , 75 ]. Moreover, otters less than 2 years old are often dispersing individuals that move extensively and may result in being more prone to fatalities.…”