Dietary analysis of Eurasian otters (Lutra lutra) from Lower Saxony

Project description

Eurasian otters (Lutra lutra L. 1758) are considered top predators in the freshwater ecosystem. They are therefore ideally suited to detect the bioaccumulation of persistent environmental pollutants via the aquatic food chain. The analysis of the diet composition of apex predators can help to elucidate the pathways of such pollutants into the aquatic environment. Otters feed mainly on fish. In general, however, the species is considered opportunistic in its choice of prey, so that amphibians, crustaceans, smaller birds and mammals as well as insects and molluscs may also be part of the prey spectrum. However, the share of the different prey classes in the diet is subject to fluctuations (e.g. spatial, seasonal, age-related). As semi-aquatic species and good swimmers, otters can hunt for prey excellently in the water as well as in the shallow shore areas and on the shore itself. In addition to streams and lakes, they also inhabit bogs, marshes or coastal areas and use marine habitat for foraging (Carss, 1995; Kruuk, 2006; Weinberger et al., 2018).
To study the feeding ecology of otters, hard component analysis and metabarcoding are possible techniques (Berry et al., 2017; Brassea-Pérez et al., 2019). Hard component analysis (bones, bones, etc.) can be used to draw conclusions about the size of the eaten (fish) species and the eaten (fish) biomass. Metabarcoding is particularly suitable for the identification of species from which only soft tissue was consumed and is thus primarily suitable for identification at species level. As both methods complement each other, they were used together in this study. The stomach and intestine samples examined were from 71 otters from Lower Saxony (discovery years 2005-2020), which had previously been analysed for residues of all 8 anticoagulant rodenticide active substances currently approved in the European Union as part of an R + D project commissioned by the Federal Environment Agency (FKZ 3720 64 409 0) at the Federal Institute of Hydrology. A total of 44 of the otters examined had stomach contents that could be used for further identification in the context of the hard component analysis. Intestinal contents of 43 otters were analysed by metabarcoding.
The results of the hard component analysis confirm fish as the most frequently eaten prey class of otters in Lower Saxony. Furthermore, components of amphibians, plants, arthropods, and very sporadically of birds, mammals and molluscs were detected in the stomachs. The Cyprinidae family was the most frequently identified fish family. That otters are opportunistic predators that feed on a variety of fish species depending on availability in their range (Kruuk, 2006; Buglione et al., 2020) was confirmed by the metabarcoding results. The study was able to show that the combination of hard component analysis and metabarcoding is suitable to break down and describe the feeding ecology of otters in Lower Saxony. While metabarcoding could identify fish species that would otherwise have been overlooked, hard component analysis could provide estimates of the number of prey eaten.

Literature

Berry, T. E.; Osterrieder, S. K.; Murray, D. C.; Coghlan, M. L.; Richardson, A. J.; Grealy, A. K.; Stat, M.; Bejder, L.; Bunce, M., 2017: DNA metabarcoding for diet analysis and biodiversity: A case study using the endangered Australian sea lion (Neophoca cinerea). Ecology and Evolution., 7, 5435–5453.

Brassea-Pérez, E.; Schramm, Y.; Heckel, G.; Chong-Robles, J.; Lago-Lestón, A., 2019: Metabarcoding analysis of the Pacific harbor seal diet in Mexico. Marine Biology., 166, 1–14.

Buglione, M.; Petrelli, S.; Troiano, C.; Notomista, T.; Rivieccio, E.; Fulgione, D., 2020: The diet of otters (Lutra lutra) on the Agri river system, one of the most important presence sites in Italy: A molecular approach. PeerJ., 8, 1–23.

Carss, D. N., 1995: Foraging behaviour and feeding ecology of the otter Lutra lutra: a selective review. Hystrix, the Italian Journal of Mammalogy., 7.

Kruuk, H., 2006: Otters: Ecology, behaviour and conservation. Oxford University Press, Oxford, UK.

Weinberger, I.; Baumgartner, H., 2018: Der Fischotter - Ein heimlicher Jäger kehrt zurück first edit. Haupt Verlag, Bern, Austria.