Marking behaviour and census of Eurasian otters (Lutra lutra) in riverine habitats: what can scat abundances and non-invasive genetic sampling tell us about otter numbers?

Abstract

Growing human-wildlife conflicts and legal conservation obligations increased the need for precise information on Eurasian otter (Lutra lutra) population parameters for species status assessment and wildlife management measures. Scat surveys have become the method of choice to monitor species distribution range, abundance and habitat use. Although methodological concerns exist, scat abundance is often used as main indicator for otter population estimates and trends. To evaluate whether scat counts serve as good proxy for otter densities in linear stream habitats, we modelled the relationship between old/fresh scat abundance and otter numbers on two spatial scales, including also seasonal effects. Actual otter densities and marking behaviour were ascertained by genotyping of otter faeces collected at 218 marking sites along 132.6 km of four salmonid streams. Otter densities in our study areas ranged from 0.16 to 0.28 otters per stream kilometre. The age of scats and the level of spatial scale were determining factors when evaluating the suitability of scat abundance as index for otter densities. Covering large parts of an otter's territory, fresh scat abundance increased with otter density, irrespectively of season. On the spatial scale of single marking sites, the relationship was not well supported, and no relationship could be found when using old scats in the models. Otter marking behaviour and differences in marking site use intensity, as well as seasonal differences in traceability and accumulation of old scats were discussed to bias the relationship between scat abundance and otter numbers.

A beacon of dung: using lemming (Lemmus lemmus) winter nests and DNA analysis of faeces to further understand predator–prey dynamics in Northern Sweden

“…This would allow for suitable preservation of faecal DNA until late June and early July, when samples were collected. DNA is known to rapidly degrade when subject to adverse weather conditions, such as prolonged exposure to UV radiation or rainfall (Davison et al 2002;Harrington et al 2010) and low-quality DNA is strongly correlated to scat freshness (Nsubuga et al 2004;Hájková et al 2006;Sittenthaler et al 2020). We therefore attribute the non-successful amplification to these factors.…”

Assessing the current feces identification method of the European otter Lutra lutra

“…The issues raised are problems regarding variation in the frequency of seasonal as well as individual marking (Kruuk 2006) but also the traceability could vary across seasons (Kruuk et al 1986, Reuther et al 2000, Lampa et al 2008. Consequently, Sittenthaler et al (2020) investigated the relationship between spraint-abundance (old and fresh) monitored along a stream and population density together with marking behavior connected to individuals and/or sex-specificity using genetic monitoring. They observed that age of spraints and the spatial scale of the monitoring were the critical factors for indexing the otter density using spraint counts.…”

“…This was caused by the fact that it was easier to find fresh spraints with increased population densities when a large part of the territories was covered, while this relationship was not found in single marking sites. Thus, Sittenthaler et al (2020) further concluded that only fresh spraints should be used for assessment of population density and trends, and old spraints can be used for surveillance of distribution and expansion.…”

Factors influencing genotyping success and genotyping error rate of Eurasian otter (Lutra lutra) faeces collected in temperate Central Europe

“…Hence, it is not surprising that the genetic analysis of otter (Lutrinae) faeces is deemed as notoriously tricky (Lerone et al 2014;Klütsch and Thomas 2018) and characterized by high dropout rates (about 50%; e.g. Hájková et al 2009;Mowry et al 2011;Silveira Trinca et al 2013;Vergara et al 2014;Sittenthaler et al 2015;Biffi and Williams 2017;Sittenthaler et al 2020). Nevertheless, when studying otter species, faeces are the sample material of choice, as otters are elusive living animals depositing scats (so-called spraints) regularly at conspicuous marking sites close to the water body (Kruuk 2006).…”