Spraint Analysis Research Articles

Trophic diversity of the otter (Lutra lutraL.) in temperate and Mediterranean freshwater habitats

AbstractAimTo analyse the geographical patterns in the composition and diversity of otter's (Lutra lutraL.) diet and their relationship with climatic characteristics.LocationEuropean freshwater habitats under Mediterranean and temperate climatic regimes.MethodsThirty‐seven otter diet studies were reviewed, twenty‐one from temperate and sixteen from Mediterranean areas. All studies were based on spraint analysis and their results expressed as relative frequency of occurrence of seven main prey categories. Principal Component Analysis was performed to extract the main gradients of diet composition. Pearson's correlation andt‐tests were used to assess the relationship between diet characteristics (composition, diversity and taxonomic richness) and geographical and climatic variables.ResultsA clear latitudinal gradient in diet composition was observed. Otter diet was more diverse and featured more prey classes in southern localities, while the species was more piscivorous towards the north, where it predated upon a higher number of fish families. This pattern was similar when temperate and Mediterranean localities of Europe were compared. Mediterranean otters behaved as more generalist predators than temperate ones, relying less on fish, and more on aquatic invertebrates and reptiles.Main conclusionsGeographical differences in otter feeding ecology in Europe seem to be related with the two contrasted climatic conditions affecting prey populations. The otter can act as a highly specialized piscivorous predator in temperate freshwater ecosystems, which do not suffer a dry season and have a comparatively stable water regime compared to Mediterranean ones. However, the unpredictable prey availability in Mediterranean areas, affected by strong spatial and temporal water shortages, favours a diversification of the otter's diet.

Otter Lutra lutra predation on farmed and free‐living salmonids in boreal freshwater habitats

In this paper we aim to define whether fish farms or stocked trout streams substantially contribute to the diet of otters Lutra lutra living in freshwater habitats of Mid‐Finland. Diet was assessed using spraint analysis. We especially focused on areas with fish farms and stocked trout Salmo trutta streams (salmonid‐rich habitat) and used ‘normal’ (salmonid‐poor) habitats as control. Frequency of salmonid remains in spraints was significantly higher in salmonid‐rich habitats than elsewhere in all seasons, the difference increasing from summer to winter. In salmonid‐rich habitats, however, salmonid consumption was not strongly seasonal. Data from spraint collection indicated a shift in activity towards salmonid‐rich habitats in winter. Otters therefore seem to switch prey seasonally, due to seasonal variation in the availability of other prey categories, by choosing to forage in particular, predictable habitats. Furthermore, our results suggest that, in salmonid‐rich habitats, the increase in salmonid frequency is to a larger extent due to the presence of fish farms than that of trout streams. Fish farms, and to a lesser extent stocked streams, may therefore constitute seasonally important feeding grounds for otters.

Examination of some factors affecting selection of fish prey by otters (Lutra lutra) living by eutrophic fish ponds

AbstractIn this study the predation and fish prey selection of otters Lutra lutra L. living by eutrophic fish ponds on agricultural land and in a protected area of temperate climate in Hungary were investigated. The correlations between fish in the diet of the otters (by spraint analysis involved 1942 and 1280 samples for the two habitats) and the fish stock available (by harvest and sample fishing) were generally close. Prey selection was significantly related to selected species of a particular size range (P<0.01). The preference calculations were performed with Ivlev's index of preference (Ei, minimum −1, maximum +1). Regardless of species, the otters avoided (Ei=−0.51) fish heavier than 1000 g, with a preference for individuals weighing between 500 and 1000 g (Ei=0.79). No substantial or clear preference was observed in the weight range below 500 g (Ei=−0.02–0.38). The preference for fish in accordance with their characteristic sites of occurrence within the body of water was also significant (P<0.01). They avoided fish living primarily in open water (Ei=−0.64) and to a lesser degree those occurring near the pond bed (Ei=−0.22). They favoured fish inhabiting the area with a covering of aquatic plants (Ei=0.46), and showed a preference to a lesser degree for fish living in the shallow littoral regions (Ei=0.14). With the cessation of fish farming and the effect of the drastic changes which occurred in the vegetation, the otters fed substantially on the stock of alternative sources of prey such as amphibians and water insects as well as terrestrial animals, and at such times, depending on season, fish became a secondary source of prey.

Seasonal variation in the diet of Cape clawless otters (Aonyx capensis) in a marine habitat

Seasonal changes in the diet of Cape clawless otters Aonyx capensis feeding in the surf zone in False Bay, Western Cape Province, South Africa, were investigated by spraint (faecal) analysis. The most common prey species, during all seasons, was the Cape rock crab, Plagusia chabrus. The next most important prey species was the Cape rock lobster, Jasus lalandii, with the fish species Clinus superciliosus being equally important in winter. Other prey were fresh-water crabs, Potamonautes perlatus, octopus, Octopus granulatus, and 17 other species of fish, frogs and mammals. In winter and autumn the most important prey category was fish while in spring and summer, crustaceans were the most important. Diversity of prey was lowest in winter, increasing through the seasons from spring to autumn.

Cyprinid prey remains in otter Lutra lutra faeces: some words of caution

AbstractThis study investigates errors associated with the recovery of cyprinid remains in otter Lutra lutra spraints. Cyprinid fishes (Cyprinidae – the carps) comprise the largest family of freshwater fishes in the world with around 2000 known species. They form the major group of freshwater fishes in Europe with a total of 80 species, 16 of which occur in Britain (Winfield & Nelson, 1991). These fishes are commonly taken by otters Lutra lutra throughout the predator's geographical range, their prevalence in the diet apparently varying in relation to their abundance. No more than three species are commonly recorded as otter prey in Britain, Ireland, and Scandinavia (e.g. Wise, Linn & Kennedy, 1981; Kyne, Smal & Fairley, 1989; Erlinge, 1967, respectively), while at least five are in eastern Poland and southern Spain (e.g. Brzezinski, Jedrzejewski & Jedrzejewska, 1993; Lopez‐Nieves & Hernando, 1984, respectively). These fishes offer an opportunity to investigate otter prey selection on relatively complex prey communities (cf. Carss et al., 1998) as they form mixed‐species assemblages (Winfield & Nelson, 1991). However, Carss (1995) concluded that if studies of otter feeding ecology were to become more than mere lists of prey items, there was an urgent need to quantify current spraint analysis techniques and their associated errors more rigorously than before. This is undoubtedly true for studies which attempt to determine the species‐ and size‐composition of cyprinids in the diet of otters.

Otter diet in relation to fish availability in a fish pond in Hungary

The food composition of otters Lutra lutra (Linnaeus, 1758) was investigated in an artifically established fish pond of 12 ha in south-western Hungary between December 1991 and November 1994. In the fish pond fish farming was carried out with the introduction of sifferent species during the first two years of the investigations, while the filling up of the pond with water and its planting did not come about the third year. The diet of otters was examined by spraint analysis (873 samlpes).

Errors associated with otter Lutra lutra faecal analysis. I. Assessing general diet from spraints

Althoug frequency of occurrence (either as percentage or relative frequency) is the most common method of expressing the content of otter Lutra lutra faeces (spraints), the accuracy of the method, and the effects of varying sampling procedures (e.g. inter‐collection interval) and sample sizes, have not been quantified. The validity of the technique was assessed in the present study by feeding trials involving captive, tame otters and computer simulation of various spraint sub‐sampling regimes. Four animals were fed known quantities (numbers and biomass) of a total of nine fish species, two bird species and one mammal over a 28‐day period. Most prey remains were passed in spraints within 24 h, although perch Perca fluviatilis scales appeared up to 10d after consumption. Remains from single meals of perch were recorded in 60 subsequent spraints from two otters, and remains of individual eels Anguillu anguilla were recorded in up to 11 spraints. Some single spraints contained the remains of up to seven individual salmonids, Salmo spp. Minnows Phoxinus phoxinus placed within the body cavities of larger rainbow trout Onrorhynchus mykiss were easily identified in spraints, as were the remains of Dytiscus spp. beetles which were not included in trial meals. The latter confirms that otters actively consumed large free‐swimming insects. Spraint analysis accurately determined the rank order of prey groups for individual otters and for all four combined. However, few of the true proportions consumed fell within the 95% confidence limits calculated from spraints. Over the month‐long trial, the overall picture of otter diet was altered little by increased inter‐sampling period for spraints. But as samples were reduced, coefficients of variation for the mean estimates of each prey group increased and were often too large for estimates to be meaningful. It is not possible to quantify otter diet accurately by frequency of occurrence methods, and the results of previous studies attempting to quantify the amount of a specific prey item consumed by otters using this method must be treated with caution. Diet could be estimated more accurately from spraint analysis by concentrating on the main prey species and using keybones, which are resistant to digestion, to determine relative size‐frequency distributions.

Analysis of otter (Lutra lutra) spraints: Part 1: Comparison of methods to estimate prey proportions; Part 2: Estimation of the size of prey fish

The accuracy of five different methods used in spraint analysis for extimating prey proportions is tested through a feeding experiment with three otters in captivity. Estimated prey proportions are copared to the actual diet of the otters. The results of analysing 362 spraints and the time budget indicated a score‐bulk estimate to be the most appropriate method of estimating prey diet and it is concluded that dietary studies using different methods can be compared in broad outlines. The relatins between the methods are confirmed in the analysis of 978 spriaints, collected in the field.

Seasonal and area‐related variations in the diet of otters Lutra lutra on Mull

The diet of otters Lurra lutrn living in a sea loch on the Isle of Mull was described by means of spraint analysis. Seasonal and spatial differences in the spraint composition were explored in the context of fluctuations in prey availability, as revealed by trapping. Butterfish Pholis gunnellus and the cottids Myoxocephalus scorpius and Taurulus bubalis were the most commonly occurring prey in spraints. In the winter, the proportion of rocklings (Ciliata spp. and Gaidropsarus spp.) and non‐rockling gadoids (Gadidae) in the diet increased. Their relatively large size makes these latter species an important constituent of the winter diet. Seasonal and spatial variation in fish consumption largely reflected fluctuations in availability. The mean size of principal prey fishes in spraints was similar to that observed in the traps. These observations suggest that otters were not strongly selective with regard to fish species and size. Shore crabs, in contrast, were not taken in proportion to availability. The findings are discussed in the light of other studies of the diet of coastal otters. It is suggested that the lack of selectivity demonstrated in this study, compared with previous studies, may be explained by area‐related variations in prey availability.

The food of otters Lutra lutra in different habitats in Hungary

The diet of otters was studied by the method of spraint analysis. Remains of over 800 prey items were found in 270 spraints. Among these the proportion of fish was over 80%. We found no preference for any particular species of fish but small or medium-sized specimens were the most frequent in the diet. The composition of the otter's diet may reflect that of the fish stock in a particular pond or lake rather than selective predation. Nearly half of the consumed fish were considered as economically unimportant and about 20% of them were classed as economical pests.