Otter Diet Research Articles

Population dynamics of two sympatric intertidal fish species (the shanny, Lipophrys pholis and long-spined scorpion fish, Taurulus bubalis) of Great Britain

The shanny/common blenny (Lipophrys pholis) and long-spined scorpionfish/bullhead (Taurulus bubalis) are commonly encountered, sympatric species within much of Great Britain's rocky intertidal zones. Despite being prey items of the cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) respectively, and both contributors to the diet of the near-threatened European otter (Lutra lutra), little is known on the population dynamics of the temperate specimens of Great Britain. It is further less known of the degrees of sympatricity between the two fish species and to what extent they are able to coexist. The current study examines spatio-temporal distributions and abundances at various resolutions: monthly population dynamics of both species along England's Yorkshire coast and seasonal population dynamics along the Yorkshire coast and around the Isle of Anglesey, Wales. Studies of their abundances, sizes, degrees of rock pool co-occurrence and diel activities are further examined, which indicate coexistence is maintained when interspecific co-occurrence takes place only between specimens of similar sizes, thus demoting size-related dominance hierarchies.

Asian Carp in the Diet of River Otters in Illinois

Abstract Populations of invasive silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis), collectively known as “Asian carp,” are growing rapidly in Illinois and may make up a large fraction of available prey for river otters (Lontra canadensis) in larger waterbodies. Our goals were to assess the frequency of Asian carp in otter diets and compare the frequency of occurrence of prey groups (fish, crayfish, and amphibians) in otter diets between land cover types and seasons. We searched for Asian carp otoliths and pharyngeal teeth, as well as parts of other fishes, crayfish, and amphibians in 155 otter scats collected from 43 stream sites in central and southern Illinois during January−April 2013 and 2014. Consistent with previous studies, fish and crayfish were primary prey items for otters, followed by amphibians. The proportion of crayfish increased from January−February to March−April, but the occurrence of the other prey types remained similar between those periods. Land cover type did ...

Diet of otters (Lutra lutra) in various habitat types in the Pannonian biogeographical region compared to other regions of Europe.

Knowledge of the effect of habitat type and region on diet and feeding behaviours of a species facilitates a better understanding of factors impacting populations, which contributes to effective conservation management. Using spraint analysis and relative frequency of occurrence data from the literature, we described the dietary patterns of Eurasian otters (Lutra lutra) in 23 study sites within the Pannonian biogeographical region in Hungary. Our results indicated that diet composition varied by habitat type and is therefore context dependant. The differences among habitat types were however lower than expected. We noticed a decline in the fish consumption with a concomitant increase in trophic niche breadth and amphibian consumption in rivers, ponds (fish farms), backwaters, marshes and small watercourses. The main differences in diet were not attributed to the consumption of primary and secondary food types (fish and amphibians), but rather to differences in other, less important food types (mammals, birds). Using hierarchical cluster analysis, rivers and ponds could clearly be separated from other habitat types. We found the main fish diet of otters in most of these areas consisted of small (<100 g), eurytopic, littoral and non-native, mostly invasive species. Dietary studies from 91 sites in six European biogeographical regions showed that fish are consumed most frequently in the Atlantic and Boreal, less in the Continental and Pannonian, and least in the Alpine and Mediterranean regions. Comparative analysis indicated that the Mediterranean region (with frequent crayfish consumption) and Alpine region (frequent amphibian consumption) cluster separate from the other regions.

Garbage in the diet of carnivores in an agricultural area

AbstractHuman food waste is considered to be richer in carbohydrates, lipids and proteins than most natural food supplies; however, it is very well digested in scats. So, as an indication of this kind of food in the diet, we have used each indigestible, anthropogenic origin element found in faeces (e.g., glass, plastic, rubber, etc.). There are few studies discussing the importance of garbage in the diet of mammalian predators living in farmland; definitely, most focus on this issue in urban areas. We studied the contribution of garbage in the diet of raccoon dog (Nyctereutes procyonoides), red fox (Vulpes vulpes), marten (Martessp.), polecat (Mustela putorius), stoat (Mustela erminea), American mink (Neovison vison) and Eurasian otter (Lutra lutra) in the agricultural areas of western Poland in 2006-2010. In addition, we examined the spatial changes in the diet of red fox and polecat. The largest contribution of garbage was found in scats of raccoon dog (8.8%), red fox (4.8%) and marten (4.3%). The diet of polecat, stoat and Eurasian otter contained 2.5%, 1.7% and 0.2% garbage items respectively. The most frequent item was plastic. Our analysis showed that garbage consumption by red fox and polecat was greater closer to human settlements. The results reveal a continuous gradient in the garbage consumption that corresponds with the degree of synanthropization of particular species.

Harlequin Ducks (&lt;i&gt;Histrionicus histrionicus&lt;/i&gt;) Scavenge Sea Urchin Fragments from Foraging Sea Otters (&lt;i&gt;Enhydra lutris&lt;/i&gt;)

Foraging animals may risk association with potential predators to obtain otherwise inaccessible prey. We observed this strategy in wintering Harlequin Ducks (Histrionicus histrionicus) scavenging fragments of Red Sea Urchins (Mesocentrotus franciscanus) from foraging Sea Otters (Enhydra lutris) that were re-occupying an area from which they had been ecologically absent since about 1850. Harlequin Ducks, like other sea ducks, have not previously been reported scavenging from other birds or mammals. In British columbia, Red Sea Urchins have reached large sizes and densities since the removal of Sea Otter predators by the marine fur trade in the 18th and 19th centuries. Observations of Sea Otters and Harlequin Ducks were made in 4 areas, spanning a time gradient of Sea Otter occupation from 1 to 5 years. During 3 months of observations (December 2013 – February 2014), Harlequin Ducks were associated with foraging Sea Otters only at sites that were recently occupied by Sea Otters (≤ 2 months), where the proportion of urchins in Sea Otter diets was highest and where the ducks acquired urchin fragments from foraging Sea Otters. We suggest that Sea Otters re-occupying their historic range and consuming predominantly large Red Sea Urchins provide a temporarily available prey subsidy for Harlequin Ducks. Our observations document a novel effect of Sea Otters providing important prey supplementation to a marine bird when foraging in urchin-rich habitats, contributing to the overall role of Sea Otters as a keystone species.

Negative interactions between giant otters (Pteronura brasiliensis) and local fisheries in the Amazon and Orinoco basins in Colombia

The apparent population recovery of giant otters during the last ten years in the Amazon and Orinoco basins in Colombia is creating serious conflicts between local fisheries and this species. This paper presents evidence of conflicts in the Orinoco, Meta and Bita rivers in the Orinoco basin, in the Inírida and Guaviare rivers, and in the Caquetá, Putumayo and Amazon rivers in the Amazon region. In most cases, fishermen are killing giant otters or are asking the government authorities to take action to reduce their numbers. Preliminary evaluations of giant otter diets indicated little competition with local fisheries. However, areas with more intense conflicts corresponded to regions with strong fishing pressure and bad management practices. We conclude that interference with fisheries by giant otters is relatively low but it is necessary to undertake management of the fisheries in the region to avoid perceived conflicts.

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

Abstract The Eurasian otter Lutra lutra is a top predator that feeds mostly on fish. Yet, studies show the high plasticity of otter foraging behaviour and the varying importance of alternative food types in the species' diet. The aims of this study were, firstly, to demonstrate by meta‐analysis how the diet composition of otters varies depending on the habitat occupied, in terms of the types of land use, waterbody, and bank vegetation. Secondly, we tested whether the choice of method of presenting prey percentages in the diet of otters influenced the conclusions of the meta‐analysis. The percentage of fish in the diet was greater for otters occupying standing water than for those occupying flowing water; was higher for otters in waterbodies overgrown by reed vegetation; and varied depending on the type of surrounding land use. However, the results of the meta‐analysis varied depending on which of the two most common methods of diet analysis were used: percentage biomass or relative frequency of occurrence (RFO). We showed that the plasticity of otter feeding behaviour might be explained by the various habitats occupied by otters. Habitat differences reflected in otters' diets might have importance for the maintenance and conservation of local populations of this species. The high diversity of methods used by researchers to report the results of dietary studies precludes full comparisons and synthesis. This demonstrates the importance of unification of reporting. Moreover, the conclusions reached by the authors of any particular study might be highly dependent on the method they applied. Thus, care should be taken when comparing ecological studies based on different methods.

Dietary specifications reflect the feeding behaviour of the European otter (Lutra lutra) in “Strandzha” Natural Park (Bulgaria)

Abstract Within the scope of the present study a field survey in the area of “Strandzha” Natural Park in south-east Bulgaria was carried out. The main goal of the investigation was to gain more detailed information on the diet of the European otters (Lutra lutra) that inhabit the park. As indicators for the presence of the mustelids a set of standard procedures, such as footprints tracking and inspecting the terrain for otter spraints were used. A total of 204 excrements were found, measured, documented and then disintegrated in water. The food rests in the faeces were investigated and the diet of the local population was documented. On the base of the results we separated the excrements into six groups and analysed the relations between the contents of the spraints and the characteristics of the habitat where they were found. We discovered a clear tendency toward piscivory in the middle and down streams of the studied rivers in the Natural Park. In the upper streams, otters relied almost exclusively on invertebrates like bivalves and crayfish as food source. The fact, that even suboptimal habitats, which offered invariable menu, were exploited by the otters is an indication for the stability of the local population.

An Assessment of Spatial and Temporal Variation in the Diet of Cape Clawless Otters (Aonyx capensis) in Marine Environments

We studied the diet of Cape clawless otters (Aonyx capensis) at three sites along the eastern and southern coast of South Africa to assess possible spatial variation along a community species richness and biomass gradient associated with rocky shores. A total of 309 spraints representing two seasons (summer 2013/2014 and winter 2014) were collected and subsequently analysed. The percentage occurrence and percentage dry mass of numerous prey categories were compared between sites and seasons. Variation in the importance of prey items was found between sites, whilst no variation was found between seasons within the same site. Crab was the most important prey item in the southernmost study area (Tsitsikamma National Park) and at the northernmost study site (KwaZulu-Natal Coast), whilst lobster was the most important prey item in the central area (Mkambati Nature Reserve). Fish was the second most important prey item at all three sites. Our results suggest that otters are opportunistic feeders that are likely able to adapt to potential prey species and abundance changes associated with current and future anthropogenically driven changes. Furthermore, long-term, site-specific stability in diet suggests that monitoring the diet of otters could provide some useful information on the status of shoreline communities.

Fish selection by riverine Eurasian otters in lowland England

Eurasian otters (Lutra lutra) may conflict with humans using fish stocks for food, income or recreation. Understanding fish selection by otters is important for predicting and managing potential conflicts. We used spraint analysis to describe the diet of Eurasian otters on rivers in the Upper Thames Valley, lowland England, in summer and winter, focusing specifically on the species and size of fish consumed. We assessed the proportion of fish consumed that were of potential commercial or sporting value (the ‘Potential Value’ category). Within this group, we assessed relative selection for family and length by comparing fish found in otter diet with their local availability. Local availability was estimated from UK Environment Agency electrofishing survey data. Fish represented 46 % (relative frequency of occurrence, RFO) of total otter diet, with fish of Potential Value representing 19 % (RFO). In the Potential Value category, cyprinids were relatively avoided; percids and esocids were relatively preferred. Most (∼80 %) fish prey items originated from fish 4–13 cm in length, 3 % from fish > 20 cm. Smaller (0–10 cm) percids and cyprinids, and larger (16–20 cm) esocids, were preferred. In summer, diet was broad, comprising 31 % (RFO) fish, 24 % birds and 14 % crayfish. In winter, diet was predominantly fish (68 % RFO) with crayfish and birds accounting for ∼5 % each. In summer, most fish consumed (70 % RFO) were the relatively slow-swimming common bullhead (Cottus gobio). Significantly more of the faster-swimming cyprinids were consumed in winter, presumably because they are easier to catch when the water is colder.

Seasonal diet of the northern river otter (Lontra canadensis): what drives prey selection?

Diet of the northern river otter (Lontra canadensis (Schreber, 1777)) has been examined throughout much of its range and across many habitat types. Few studies have examined prey selection based on prey abundance estimates, however, and prey selection results have been inconsistent. We determined composition, seasonal variation, and prey selection of otter diet in northern Utah comprising multiple habitat types and prey communities. We evaluated the hypothesis that otters take prey according to availability and in inverse proportion to swimming ability. Fish was the primary class of prey taken by otters (96.5%), followed by crustaceans (16.9%). Among families, otter diet was composed primarily of Salmonidae and Cottidae, the two families that dominated the fish community of the main-channel habitat. Otter diet varied seasonally for nearly all classes (G[24] = 127.8, P &lt; 0.001) and families (G[18] = 132.94, P &lt; 0.001) of prey. In particular, fish occurrence was lower during summer than during other seasons (P ≤ 0.05), whereas crustacean (i.e., crayfish (Astacoidea)) occurrence was higher (G[3] = 71.1, P &lt; 0.001). At the family level, occurrence of Salmonidae was greatest during fall (G[3] = 11.7, P &lt; 0.01). Within one of our habitat types, we found otters to select for prey in proportion to abundance and in inverse proportion to swimming ability, with otters selecting for Catostomidae and Cyprinidae, against Salmonidae, and Cottidae according to its abundance. We conclude that habitat type may be the initial driver of prey selection, while factors such as abundance, agility, and life history of prey may be secondary drivers.

River Otter Distribution and Food Habits in Grand Teton National Park as Part of an Ongoing Project in the GYE

Grand Teton National Park is part of the known range of the North American river otter, however not much is known about this semi-aquatic mammal within the park. The results presented here are part of a larger project to investigate the potential of the river otter (Lontra canadensis) to serve as an aquatic flagship (species that engender public support and action) for the Greater Yellowstone Ecosystem. River otters, known for their charismatic behavior have the potential to serve as an aquatic flagship species to promote conservation of aquatic ecosystems. The primary objective of this portion of the study was to identify river otter latrines on portions of the Snake River, between Flagg Ranch and Jackson Lake, and between Jackson Lake Dam and Pacific Creek, collect river otter scats to determine diet of the river otter, and employ remote cameras to determine activity patterns of the river otters. Between 20 June and 1 July 2015, 26 river otter latrines were identified during shoreline surveys, 186 river otter scats were collected, and cameras were deployed at 6 latrines between 7 July and 24 August 2015. River otter scats have been cleaned and prepared for analysis, but have not all been processed to date. Camera traps recorded 222 images, of which 7% (n = 14) were of carnivores, 70% (n = 155) were of non-carnivore mammals, and 9% (n = 22) were of birds. River otters were detected at 1 of the 6 latrines, a total of 5 independent times during the study.

Régime alimentaire et stratégie trophique saisonnière de la Loutre d’Europe, Lutra lutra, dans le Moyen Atlas (Maroc)

Diet and seasonal trophic strategy of the European Otter, Lutra lutra, in Middle Atlas, Morocco. To learn more about the adaptability and predation behaviour of the European Otter (Lutra lutra) in semi-arid regions, its diet has been studied in Wadi Beth, a typical river of Middle Atlas (Morocco), from its source areas (Azrou) to El Kansera hill reservoir dam. Fecal samples (spraints) were systematically collected from six locations during two annual cycles, a collection per season campaign. The study reveals that the otter’s diet is classic (dominant fish), very typical and characteristic of aquatic ecosystems in arid Mediterranean climate, which is reflected in particular by the singular presence of prey like reptiles. Prey species richness totals more than 18 species. Moreover, the frequency of occurrence and relative abundance of taxa consumed were calculated from 2444 identified prey. Fish represent more than 75 % of the prey (relative abundance) with a very large predominance of 3 species of barbels. The anuran amphibians constitute 15 % of the prey. The rest is accounted for, according their respective importance, by insects, ophidians, a chelonian (Mauremys leprosa), birds, crustaceans and finally small mammals. Over time, the diet changed : in autumn 2010, cichlids, introduced into the river, appeared in the prey consumed. The proportion of prey types abruptly changed : perciforms, rare in spring and summer 2010 (less than 4 % of the prey) increased sevenfold in autumn 2010 (27 %) and then declined in the spring and more in summer 2011. In summer 2011, the proportion of barbels dropped, drastically offset by salmonids and, even more, by amphibians. In summer, the proportion of amphibians and ophidians becomes more important. Site variations are linked to local conditions : presence of ponds, nature of the bottom, slope, speed and flow of the water, etc. Finally, small-sized fish (salmonids and barbels) dominate the diet : 80 % are less than 10 cm.

Spatial and Temporal Variation in River Otter (Lontra canadensis) Diet and Predation on Rockfish (Genus Sebastes) in the San Juan Islands, Washington

Spatial and Temporal Variation in River Otter (Lontra canadensis) Diet and Predation on Rockfish (Genus Sebastes) in the San Juan Islands, Washington

The Diet of Eurasian Otters in the Jajrood River System, Iran

Abstract The diet and feeding habits of Eurasian otters (Lutra lutra) were studied by spraint analysis over a one year period on the four sections of the Jajrood River, eastern Tehran. Two methods were used to estimate the proportions of different prey consumed: frequency of occurrence and score-bulk estimate. The number of prey categories in a spraint varied between one and four. Fish, crabs, birds and insects were found in the spraints. Fish is the main prey. Otters mainly eat fish, preferring three species: the chub (Leuciscus cephalus), riffle minnow (Alburnoides bipunctatus) and various barbel (Capoeta spp.) species. The otters' diet differed significantly across four sites positive for otter sign. Seasonal variation was also found: birds were taken more in the cold season and insects in the warm season. The proportion of crab in the diet was almost constant throughout the year. Leuciscus cephalus was the most taken fish species in the cold season and Capoeta spp. in the warm season. Only L. Cephalus...

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

ABSTRACTIn Mediterranean temporary rivers, ecological resources greatly fluctuate because of the high hydrological variability throughout the year. However, flow regulation prevents this natural regime and commonly entails associated non‐native species, which change the structure of aquatic communities. Nonetheless, few studies have tested the interaction of these two disruptive factors (flow regulation and non‐native species) and their synergistic effects on the Eurasian otter (Lutra lutra) diet at the river scale. The aim of this study was to compare the seasonal feeding habits of the otter between a temporary non‐regulated stretch and two regulated stretches invaded by non‐native species in a Mediterranean water course. The Bullaque River (Guadiana River Basin, central Spain) was seasonally sampled for otter spraints and prey abundance assessed from December 2009 to November 2010. Three stretches were considered: high (source, non‐regulated), medium (transition, regulated) and low (confluence, regulated). Diet varied from native prey in the high stretch (amphibians, insects and endemic cyprinids) to non‐native species in the low stretch (red‐swamp crayfish Procambarus clarkii and pumpkinseed sunfish Lepomis gibbosus). Seasonally, ingested biomass of native prey increased in spring. Diet was more diverse in the high stretch. Otters neutrally selected native cyprinids in the high stretch throughout the year, whereas crayfish was selected in the other two stretches. Overall results showed that flow regulation and non‐native species have increased prey availability for the otter; however, this paper highlights the importance of maintaining natural regimes in Mediterranean temporary rivers to conserve native communities and thus minimally impact food webs in Iberian freshwaters. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Seasonal variation in the diet of Lontra longicaudis in the Paraná River basin, Argentina

We studied the Neotropical otter (Lontra longicaudis) seasonal diet variations in the middle Paraná River valley, in central-northern Argentina, at the southern limit of its global range. We recorded 745 prey items in 320 scats collected over the course of 1 year in a tributary stream of the Paraná River. Fish, crustaceans, mammals, and insects were the most important items in frequency of occurrence among items. Other items, like mollusks, birds, amphibians, and reptilians were presented in low frequency in all seasons. We recorded seasonal variation in the frequency of the principal categories items: fish, mammals, crustaceans, and insects and in reptilian that had low frequency. Although fish were the most common items consumed by the otter, other groups such as crustaceans, mammals, and insects, were also important in the diet of the Neotropical otter throughout the seasons. Mammals and insects showed a higher frequency in the Neotropical otter diet in our study than in Brazil, Mexico, and even northern Argentina. We noted a marked variation throughout the Neotropical region in the niche breadth indices among studies of Neotropical otter’s diet. The Shannon H′ diversity index showed a higher value in our study than in most of previous diet analyses of this species.

Fatty acid analysis as a tool to infer the diet in Illinois river otters (Lontra canadensis).

Fatty acids (FA) have recently been used in several studies to infer the diet in a number of species. While these studies have been largely successful, most have dealt with predators that have a fairly specialized diet. In this paper, we used FA analysis as a tool to infer the diet of the nearctic river otter (Lontra canadensis). The river otter is an opportunistic predator known to subsist on a wide variety of prey including, fishes, crayfish, molluscs, reptiles and amphibians, among others. We analyzed the principle components of 60 FA from otters and 25 potential prey species in Illinois, USA. Prey species came from 4 major taxonomic divisions: fishes, crayfish, molluscs and amphibians. Within each division, most, but not all, species had significantly different profiles. Using quantitative FA signature analysis, our results suggest that, by mass, fish species are the most significant component of Illinois River otters’ diet (37.7 ± 1.0%). Molluscs ranked second (32.0 ± 0.8%), followed by amphibians (27.3 ± 4.3%), and finally, crayfish (3.0 ± 0.6%). Our analysis indicates that molluscs make up a larger portion of the otter diet than previously reported. Throughout much of the Midwest there have been numerous otter reintroduction efforts, many of which appear to be successful. In regions where mollusc species are endangered, these data are essential for management agencies to better understand the potential impact of otters on these species. Our analysis further suggests that quantitative FA signature analysis can be used to infer diet even when prey species are diverse, to the extent that their FA profiles differ. Better understanding of the otter’s metabolism of FA would improve inferences of diet from FA analysis.

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

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.

Occurrence, food habits, and activity patterns of Eurasian otters Lutra lutra in northwestern Greece: implications for research and conservation

AbstractEurasian otters (