Do non‐native fish as prey favour the conservation of the threatened indigenous Eurasian otter?

Abstract

Summary 1. Biological invasions are considered a major threat to biodiversity. Most research has focused on the distribution, biology and impacts of non‐native species on native fauna and flora. However, few studies have explored their role as prey for native predators of conservation concern. 2. To assess the incidence and intensity of predation by the Eurasian otter Lutra lutra on established non‐native fish species, data were collated from the published literature. To be selected, studies had to cover at least 1 year, analyse more than 100 spraints and report the study period and percentage relative frequency (%RF) of all prey fish species. 3. To permit reliable, time‐related comparisons with %RF of non‐native fishes in otter diet, we also reviewed available information about both the distribution of non‐native fishes and history of their introductions to European countries, revealing a decrease with longitude in the number of naturalised non‐native fishes taken (ranging between 5 and 34) and their percentage in each fish assemblage. 4. Our selective criteria were met by 30 dietary studies from 44 study areas in 15 European countries during 1970–2010. The extent to which otters rely on non‐native fishes was almost negligible (mean %RF = 4.8), with the number of non‐native fishes preyed upon by otters decreasing with both latitude and longitude. 5. The %RF of non‐native fish in the diet increased slightly with time, with otters preying significantly more on non‐native fish in study areas where alterations of the fish assemblage had been highlighted in the reference papers. No relationship was found between otter diet breadth and the occurrence of non‐native fishes in their diet. 6. The current role of non‐native species in otter diet suggests that effective otter conservation management plans should focus on the maintenance and/or enhancement of native fish assemblages.

Amphibians in Eurasian otterLutra lutradiet: osteological identification unveils hidden prey richness and male‐biased predation on anurans

“…, Balestrieri et al. ), we could not highlight any latitudinal trend, but the frequency of amphibians in otter diet increased with longitude: the highest %RFs were recorded in the eastern Alpine region (Poland and Bulgaria) and in Boreal regions (Finland, Belarus; see also Lanszki et al. ).…”

“…More recently, Balestrieri et al. () found no relationship between otter dietary breadth and latitude, suggesting that habitat‐related variations in fish assemblage richness and stability play a major role in shaping otter diet. Accordingly, otters prey on fish more frequently in standing waters surrounded by riparian vegetation than in flowing waters in open habitats (Krawczyk et al.…”

“…Although %RF does not provide any information about the biomass or relative volume of each prey item, this index has the advantage of having been used frequently in inter-population dietary comparisons (e.g. Reynolds & Aebischer 1991, Zhou et al 2011, and particularly in otter dietary studies (Balestrieri et al 2013, Krawczyk et al 2016, Lanszki et al 2016. For otters, %RF values have been shown to be nearly as accurate as other indices (Jacobsen & Hansen 1996).…”

“…However, unlike fish remains, amphibian remains are rarely assigned to species level in dietary studies, and therefore information on the diversity of this important alternative resource is generally scarce (but see Clavero et al 2005 andParry et al 2015). Although several previous reviews have analysed range-scale variability in otter diet, they were mainly focused on fish prey and the effects of variation in its use or availability on the consumption of secondary food resources (Jedrzejewska et al 2001, Clavero et al 2003, Balestrieri et al 2013, Krawczyk et al 2016, Lanszki et al 2016. Following on from Ruiz-Olmo's (1995) review on otter predation of reptiles, we reviewed the available literature with the aim of outlining the level of detail currently applied to the class Amphibia in otter dietary studies, and the overall pattern of use of this resource by otters throughout their European range.…”

EFFECTS OF FLOW REGULATION AND NON‐NATIVE SPECIES ON FEEDING HABITS OF EURASIAN OTTER Lutra lutra IN MEDITERRANEAN TEMPORARY RIVERS

“…Considering the whole river and the entire year, the otter diet resembles that typical of regulated water courses and reservoirs, that is, based on red‐swamp crayfish and non‐native fish species (López‐Nieves and Hernando, ; Adrián and Moreno, ; Delibes and Adrián, ; Pedroso and Santos‐Reis, ; Sales‐Luis et al ., ), instead of that typical of Mediterranean temporary rivers (Ruiz‐Olmo et al ., ; Bartolomé, ; Clavero et al ., ). Possibly, the opportunistic predatory behaviour of the otter (Balestrieri et al ., ) allows them to feed on the most abundant prey (Erlinge, , Taastrom and Jacobsen, ). In our study, red‐swamp crayfish, the most abundant prey in the river, was also the main otter prey.…”