Resource availability and use by Eurasian otters Lutra lutra in a heavily modified river‐canal system

Abstract

The freshwater habitats of semi‐aquatic carnivores in Europe have undergone substantial alterations due to regulation and construction of artificial watercourses. We compared seasonal estimates of otter Lutra lutra food composition with concomitantly collected data on fish availability and otter holt location in a strongly human‐modified ecosystem comprising the upper stretches of the Wieprz‐Krzna Canal, the longest artificial waterway in Poland, and an associated regulated river. Concrete lining of the canal, extreme water level variation and regular vegetation clearance to enhance water flow substantially limited otter food and shelter resources, yet the canal offered attractive habitats for some fish and hibernating amphibians, while otter resting sites were available at the closely adjacent river. The taxonomic composition of fish in the otter diet, reconstructed based on faecal analysis, was largely reflected in electrofishing catches. Fish communities in our study area were numerically dominated by small‐sized species and otters fed on very small fish (median seasonal total lengths: 46‐54 mm). Either the smaller fish in the population were taken or prey sizes did not differ from those available. The significant contribution of amphibians and waterbirds to otter diet (seasonally 41‐75% in terms of biomass) indicated poor fish supplies for otters in the canal‐river system. High trophic diversity, compared to other otter studies in temperate climatic conditions, indicates that otters facing unstable food conditions exhibit great flexibility in their diet, which may facilitate colonisation of anthropogenic, depauperate environments. Otter occurrence provides little opportunity for conflict with human economic interests in ecosystems that are highly managed for purposes other than fish production. Since anthropogenic habitats are typically poor in some resources, such as shelter structures, their suitability for otters can be enhanced by ensuring good connectivity with nearby less‐disturbed habitats, where the necessary resources can be supplemented.

Diet composition of the Eurasian otter Lutra lutra in different freshwater habitats of temperate Europe: a review and meta‐analysis

“…Thus, the spectrum of occupied habitats has increased, and some anthropogenic‐transformed habitats with relatively poor food resources have started to be inhabited (Kloskowski et al. ). The opportunistic feeding behaviour of otters is probably the main factor facilitating this colonisation of new areas.…”

“…However, increases in populations of otters in some regions of Europe have resulted in the colonisation of sub-optimal habitats (Romanowski 2006). Thus, the spectrum of occupied habitats has increased, and some anthropogenictransformed habitats with relatively poor food resources have started to be inhabited (Kloskowski et al 2013). The opportunistic feeding behaviour of otters is probably the main factor facilitating this colonisation of new areas.…”

Fish size selection and diet composition of Eurasian otters (Lutra lutra) in salmonid streams: Picky gourmets rather than opportunists?

“…For other fish species, length and weight were assessed by comparison of diagnostic bones found in otter spraints to our personal reference collection consisting of fish of known size. Ingested biomass of other prey categories was estimated using mean weight of specimen caught in the study sites and based on literature: insects 1 g, crayfish 50 g, mammals 30 g, reptiles 50 g, amphibians 30 g, birds 100 g (Beja, 1996;Clavero et al, 2004;Blanco-Garrido et al, 2008;Smiroldo et al, 2009;Kloskowski et al, 2013).…”

“…At stream Y, we had 1.5 times higher otter density compared to stream O (Sittenthaler et al, unpublished data), whereas stream fish availability was 3 to 6 times higher at O compared to P and Y, respectively. Intraspecific competition therefore may be higher for primary prey (fish, salmonids) at stream Y, which may also lead to higher diversification of otter diet and inclusion of alternative prey as key resource ), as also indicated by higher trophic niche breadth values (Kloskowski et al, 2013).…”

Age, Growth and Reproductive Period of White Bream, Blicca bjoerkna (L., 1758) in Lake Ladik, Turkey

“…This species does not have any commercial value because of its unpleasant taste. However, it is an important prey for top predators such as Esox lucius (Wysujack et al 2001;Yazıcıoğlu 2014), Perca fluviatilis (Wziatek et al 2004;Yazıcıoğlu et al 2012), Sander lucioperca (Lozys 2003), Silurus glanis (Wysujack and Mehner 2005), Lutra lutra (Kemenes and Nechay 1990;Kloskowski et al 2013), Mustela vison (Bartoszewicz and Zalewski 2003), and Vulpes vulpes (Jensen and Sequeira 1978).…”