The seasonal diet composition of otters (Lutra lutra) living by an eutrophic fish pond system, a wetland alder forest, and a slow-flowing stream located in south-west Hungary was investigated by spraint analysis (n = 801, 116 and 234 samples respectively). Both percentage relative frequency of occurrence (O%) and biomass (B%) of food items (calculated by coefficients of digestibility) were estimated. The food composition of the otters living by the three areas differed significantly (PAstacus spp.) was dominant (54 O% and 62 B%). Close correlation was found between relative frequency of occurrence and biomass of food items.
Endozoochory is a mutualistic interaction between plants and animals. Such a relationship has rarely been examined in the Eurasian otter Lutra lutra. This study aimed to assess the use and electivity of fruit by this carnivore, along with the viability of ingested seeds. Otter spraints and fruit were collected from the River Bullaque (Guadiana River basin, central Spain) in June and September 2018-2019. A high occurrence of fruit (> 40%) was found in spraints during September. Otters ingested fruit in June from only one plant species: Iberian bushweed Flueggea tinctoria (Phyllanthaceae); whereas seeds ingested in September belonged to four plant species: apple mint Mentha suaveolens (Lamiaceae), common hawthorn Crataegus monogyna, dog rose Rosa canina and elmleaf blackberry Rubus ulmifolius (three Rosaceae species). According to the environmental availability, otters displayed avoidance for mint and rose, neutral selection for hawthorn and preference for blackberry. Germination was unsuccessful for mint seeds, whereas germination was the highest for blackberry (37%; 49% for blackbird Turdus merula, a well-known frugivorous species). Otters appear to display an ecological role as seed dispersers for riparian vegetation in Iberian fresh waters. These findings provide insights into this endozoochorous co-evolution between plants and Carnivora.
Diet composition and feeding habits of Eurasian otters (Lutra lutra) living on three moors (Baláta, Nagyberek and Fehérvíz) in Hungary were studied over two years using spraint analysis (n = 199, 503 and 315 samples from the three moors, respectively). The food and presence of otters in the first moderate and second drought year, when the moors dried during the summer period, generally differed. Area-dependent variations in the diet were also found. The primary food source was fish (biomass estimation for the first and second year: Baláta 94.4% and 99.9%; Nagyberek 93.9% and 71.5%; Fehérvíz 66.4% and 82.1%). Most fish (mean: 94.6–99.9%) were small-sized (below 100 g in weight), and the most frequently taken species was Carassius spp. On moors, which are dependent on rainfall and ground-water only, during or after periods of drought otters temporarily changed their diet from optimal prey (fish) to sub-optimal prey (e.g., waterfowl) and they often left the habitat entirely. On moors with small canals, during periods of drought otters kept fish as the dominant food source, and weathered out extreme environmental local conditions.
In early spring of 2007, unusual feeding behaviour was observed for the Eurasian otter (Lutra lutra) when a cache of toads (n = 18), black bullheads (n = 2) and great diving beetles (min. 58 ind.) were found in a hollow tree-trunk on the shores of an oxbow lake near the River Danube. Spraint analysis identified the primary food of otters in the area to be fish, with non-fish (buffer) prey of very low importance. As the otter consumed almost exclusively fish, and appeared to store mainly buffer food items, this may indicate that either preferred fish were less available (limited) or that non-fish items were relatively more abundant for a short period during the mild ‘cold’ winter and spring period. The otter had abandoned this particular cache. Food caching is an important dietary adaptation for many species, providing readily available food during periods when fresh food may be difficult to find.
The diet of the otter (Lutra lutra L.) was assessed through spraint analysis at three different streams in the Beskydy Mountains (north-east Czech Republic) and compared with fish availability and river management procedures. The remains of 3 478 prey items were recorded in 894 spraints, collected between May 2000 and May 2002. Fish were the dominant species taken (90%), followed by amphibians (50%). The most frequently occurring species of fish were the Carpathian sculpin Cottus poecilopus (71%) and brown trout Salmo trutta m. fario (65%). The composition of the otter’s diet tended to reflect the fish availability (biomass) in streams. Despite the general similarity of the different streams studied, diet composition differed significantly. The differences in diet could be explained by differences in fishery management (stocking) together with the location of migration barriers.
Bones were obtained from three fish species (brown trout Salmo trutta m. fario, grayling Thymallus thymallus and Carpathian sculpin Cottus poecilopus) for regression analysis. Bones used were chosen based upon frequency of occurrence in spraint samples and diagnostic value. Relationships between the length of diagnostic bones and fish length, fish length and weight, and standard length to total length, were assessed for the three fish species. Polynomial regression was deemed most suitable for the relationship between bone length and fish standard length, multiplicative between fish standard length and fish weight, and linear (brown trout) or polynomial (grayling and Carpathian sculpin) for standard length against total length. All calculated regressions were highly significant and displayed high coefficients of determination, ranging between 93.9 and 99.8 %. The uses of the bones examined, and the equations produced, are discussed in the light of their future use in estimating prey numbers, length and biomass in otter diet analysis.
Research in freshwater ecology has traditionally focused on water courses or large still waters. However, ponds support proportionately high levels of biodiversity relative to other inland waters in Europe, and foraging by Eurasian otter Lutra lutra (L., 1758) could have considerable impacts on species composition in these small water bodies. The aim of the present study was to analyse otter spraints around ponds during two contrasting seasons (winter and spring) in north Norfolk (eastern England), where both otter and ponds are of particular conservation concern. Spraint density, prey diversity and the consumption of river-associated species were higher in spring than winter. In both seasons, birds were the most important prey category as ingested biomass. European eel Anguilla anguilla (L., 1758) and amphibians, specifically common frog Rana temporaria L., 1758 and common toad Bufo bufo (L., 1758), were more consumed in spring, whereas northern pike Esox lucius L., 1758 and tench Tinca tinca (L., 1758) were taken in winter. Non-native common carp Cyprinus carpio L., 1758 was important in both seasons, whereas threatened native crucian carp Carassius carassius (L., 1758) was a minor prey item. Massive kills of common toad, which involved a new handling technique for predation on this species, were observed mainly in spring. The study demonstrated otters to display great plasticity in foraging behaviour and contributes to the
understanding of otter predatory pressure on pond biodiversity, with implications for landscape management.
Otter (Lutra lutra) diet was studied by analysing of 180 spraints and 29 partly consumed fish remains found in winter around fishponds in South Bohemia (Czech Republic). The proportion of fish found in spraints was 95.6% of all prey items, roach (Rutilus rutilus), topmouth gudgeon (Pseudorasbora parva) and common carp (Cyprinus carpio) being the most numerically abundant species with 37.3, 21.3 and 19.0% respectively. Carp dominated the diet bymass (47.8%), whilst roach and “other commercial fish species” (predatory and herbivorous fish, tench, Tinca tinca) formed 21.8 and 15.3% of total biomass, respectively. Small fish (< 200 mm) predominated in the diet and only 4.0% of all fish found in spraints exceeded 300 mm TL. Large fish remains were very scarce in spraints and were best recorded from uneaten prey remains. The partially eaten remains of carp, pike (Esox lucius) and common bream (Abramis brama) were found on banks or ice, but most (86%) were carp. The original length of carp corpses ranged between 283 and 530 mm TL, and the proportion of body mass consumed varied between 5.0 – 90.1%. The length of pike remains ranged from 386 to 754 mm TL, of which 84.0% of body mass on average was consumed by otters. The otter diet apparently reflects food availability in fishponds and supply channels. Small water basins with a high stock density can be vulnerable to serious damage especially during the winter period and at such places, where no better accessible source of food is available to otters. However, in many such places simple mitigation measures may be able to reduce otter predation.