• Assessment of Eurasian otter population size and structure using a non-invasive genetic method
• Study of fish communities as otter food supply
• Feeding ecology of otters

Assessment of Eurasian otter population size and structure using a non-invasive genetic method

 

The Eurasian otter (Lutra lutra) is one of the most studied mustelid species in recent years, however, many basic population parameters, such as effective population size and sex ratio, are still not fully understood. Over most of its distribution, otters are night active and very elusive in their behaviour and spraints (otter faeces) usually represent the only available biological material. Spraints contain cells shed from the gut lining and thus DNA from its owner can potentially be extracted and analysed. Genetic analysis of faeces using microsatellite (highly variable simple sequence repeats) and SRY (a male specific gene located on the Y chromosome) markers can provide identification of individuals, sex, relatedness, estimates of population size and the level of genetic polymorphism within or between populations, all without direct contact with the animals. The method, however, has limitations resulting either from low DNA quantity, low DNA quality (i.e. degraded DNA) or poor extract quality (i.e. PCR inhibitors). In 2003, a project was started which aims to assess otter population size and structure in two different habitats in the Czech and Slovak Republics. The project includes initial testing and optimisation of the methods (ref.2), investigation of population size and structure of otters at two sites - a fishpond area in the Třeboň CHKO & BR, and a mountainous area in the Slovenský Raj National Park (ref.3), and a study of genetic diversity and population genetic structure of otter populations in the Czech and Slovak Republics (ref.1). This research is funded by the Grant Agency of the Czech Republic (principal investigator J. Zima), and conducted in cooperation with the Czech Otter Foundation Fund, Třeboň, and the Administration of the Slovenský Raj National Park, State Nature Conservancy of the Slovak Republic.

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Study of fish communities as otter food supply

Fishes are of primary importance in the diet of the otter. Therefore, species composition, abundance and biomass, and especially availability of fish, significantly influence the occurrence and abundance of otters. To understand the relationship between otter numbers and fish productivity, studies of fish communities are an essential prerequisite.

We studied species composition, abundance, biomass, and size structure of fish at 14 different sites in the upper Hornád River catchment, Slovakia. In this area, a simultaneous research project on otter diet and assessment of otter numbers is being carried out.

This work is supervised by Pavel Jurajda.

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Feeding ecology of otters

Within the study of the relationship between otter numbers and fish productivity within the upper Hornád River catchment, Slovakia, research on otter diet is being carried out. The study area consists of 14 different sites, comprising stretches along 2 mountain streams and a sub-mountain river, and diet composition is studied using spraint analysis. This study follows on from my research for my diploma thesis (ref.5).

Identification of undigested remains in faeces is the most common method of analysing the diet of piscivorous predators. However, besides basic identification of prey species, additional information on numbers, size and quantitative proportion (biomass) of different species in the diet is often required. Therefore, regressions between bone length, fish length and fish weight were produced (ref.4) for the three most common fish species at the study area (brown trout, grayling, Carpathian sculpin). These regressions enable estimates of biomass composition of prey items in the diet, the method considered as most closely quantifying actual diet composition.

This research is conducted in cooperation with Kevin Roche (Czech Otter Foundation Fund) and Bedřich Hájek (State Nature Conservancy of the Slovak Republic, Administration of Slovenský Raj National Park).

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