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In a field survey of Poland in 1991-1994, signs of otters Lutra lutra {Linnaeus, 1758) were found at 1655 (79.5%) of the 2083 investigated sites. Widespread in most of the country, otters were especially common in the lakelands (N Poland), along the western and eastern borders, and in the Karpaty/Carpathian Mts (SE Poland). Two large areas with only few positive sites were identified in Śląsk/Silesia (SW Poland) and central Poland. Otters inhabit the majority of large rivers in Poland, except some sections of Odra/Oder and Wista/Vistula. The dynamics of the otter population in Poland in recent decades is difficult to investigate, mainly due to the scarce question­naire data from the sixties and seventies, however, present records suggest that the otter has extended its range, and is no longer an endangered species in Poland.
Estimating animal population size is a critical task in both wildlife management and conservation biology. Precise and unbiased estimates are nonetheless mostly difficult to obtain, as estimates based on abundance over unit area are frequently inflated due to the “edge effect” bias. This may lead to the implementation of inappropriate management and conservation decisions. In an attempt to obtain an as accurate and conservative as possible picture of Eurasian otter (Lutra lutra) numbers, we combined radio tracking data from a subset of tracked individuals from an extensive project on otter ecology performed in Southern Portugal with information stemming from other data sources, including trapping, carcasses, direct observation of tagged and untagged individuals, relatedness estimates among genotyped individuals, and a minor contribution from non-invasive genetic sampling. In 158 km of water network, which covers a sampling area of 161 km2 and corresponds to the minimum convex polygon constructed around the locations of five radio-tracked females, 21 animals were estimated to exist. They included the five radio-tracked, reproducing females and six adult males. Density estimates varied from one otter per 3.71–7.80 km of river length (one adult otter per 7.09–14.36 km) to one otter per 7.67–7.93 km2 of range, depending on the method and scale of analysis. Possible biases and implications of methods used for estimating density of otters and other organisms living in linear habitats are highlighted, providing recommendations on the issue.
A sample of 1037 skulls of otters Lutra lutra (Linnaeus, 1758) from eastern Germany was analysed for inherent dental abnormalities. Deviations from the normal dental pattern were found in 107 individuals. A total of 150 cases were classified in 5 categories of abnormality. In considering variations from the normal number of teeth, supernumerary (polydonty, 1.7%) was more frequent than missing teeth (oligodonty, 0.9%). In most cases, numerical variations were not connected with phylogenetic background. The most frequent variations were displacement of teeth in the tooth row (6.0%) and deviations of the normal shape of teeth (3.3%). Variations of the local position of teeth occurred in 2.6% of cases. None of these deviations showed significant sex-dependent differences. Furthermore, no regional differences in the frequencies of these anomalies were noticed. Another 459 otters (822 cases) had accessory roots at P2, P3, or P4. These characters were considered as non-metrical traits and used to study epigenetic regional differentiation. The Mean Measure of Divergence segregated the Baltic coast from almost all other regions. Preliminary results of analysis of Fluctuating Asymmetry are presented, using these traits to demonstrate the utility of dental deviations for estimating influences on developmental stability. Generally, it can be stated that the dentition of otters is very stable.
One female and 2 male otters Lutra lutra {Linnaeus, 1758) were radio-tracked in the River Don catchment, Aberdeenshire, Scotland, between April 1988 and June 1990, and their range use patterns were compared. The males had longer total ranges than the female. The range of the larger male almost completely overlapped with that of the female, but the range of the smaller male was mainly separate from that of the female. The ranges of the 2 males only partially overlapped, with the larger male having the greatest total range, nightly range and rate of travel, and the lowest tendency to revisit areas during the night. The smaller male was relatively sedentary, using two separate core areas, whereas the other 2 otters had single core areas and frequently patrolled their total ranges. As the larger male was sexually active, but the smaller one did not appear to be, it was argued that the need to search for mates could explain some of these differences in spatial patterns. All 3 otters used tributaries more than expected based on the areas within their total ranges. This may be because riparian margins were used in greater proportion than central areas of the channel width.
The food composition of otters Lutra lutra (Linnaeus, 1758) was investigated in an artificially 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 different 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 in the third year. The diet of otters was examined by spraint analysis (873 samples). The most important prey of otters was fish amounting 40 to 100%; the variation was due to season, method of farming and density and composition of the fish stock available. There was a close relationship between the frequency of occur­rence of different fish species in the otter diet and the amount of fish available to the otters. The correlation coefficients (rp) were 0.56 (p < 0.05), 0.87 (p < 0.0001) and 0.93 (p < 0.0001) in the three years. Fish species that are predominant in the fish pond were the most frequent in the otter diet. Most of the fish eaten were below 50 g, ie 55, 88 and 90% respectively in the three years. Prey fish weighing more than 1000 g were found in scats only in the second year, and in a low proportion (1%). Economically important fish species constituted 33, 9 and 3% of the otter diet in the three years. The economic consequences of otter predation on fish are discussed.
Adult and sub-adult otters Lutra lutra (Linnaeus, 1758) caught and consumed 3.36 prey (fish) per hour (n = 32 captures). This represents 273.8 g of wet mass/h of activity outside the rest sites (10.5-13.1% of the day) and it is enough to get their daily needs. Otters ate the prey without hiding on average (n = 93) 0.46 m from the bank (up to 3.9 m) and 0.25 m above water level (up to 2.05 m). Prey weighing less than 150-200 g were consumed entirely; for this reason prey remains are very rare (except large trout, American crayfish and gravide cyprinid females). Unpleasant tasting or toxic parts and sharp or wide parts of the bones, scales, teeth, claws, heads or leggs in large prey were not eaten.
The diet of the otter Lutra lutra (Linnaeus, 1758) was studied in the Bieszczady Mts (south-east Poland), at four locations situated on the small rivers from October 1987 to June 1989. In ail, 379 samples of spraints were analysed and 1687 animals preyed upon belonging to various systematic groups were identified. Frequency analysis indicated that most of the prey was fish (63.4%) with insects contributing 20.2% and amphibians 14.5%. Among fish the most frequently occurring were Phoxinus phoxinus (frequency - 15.0%), Cottus sp. (14.4%) and Noemacheilus barbatulus (9.0%). Relatively low frequencies were found for Salmo trutta (5.7%) and Thymallus thymallus (3.1%). Percentage analysis indicated that most of the diet comprised fishes (73.2% of biomass) and much less amphibians (26.8%). Among fish species S. trutta dominated (42.4% of all biomass) over Coitus sp. (10.2%) and N. barbatulus (3.9%).
The diet of otters Lutra lutra (Linnaeus, 1758) in central Finland was studied in 1988-1993 by analysing 1506 spraints. The main components of the diet of otters are fish and amphibians. The most important fishes for otters are small (body length mostly less than 15 cm) cyprinids, perches and pikes. The composition of food varies seasonally. In winter amphibians are the most important prey (33.2% of all food). Perches, pikes and cyprinids are important during all seasons, but in winter small sculpins (9.8% of the food) and burbots (8.9%) are also important. In spring the most important prey are cyprinids (38.7% of the food). Amphibians are important, especially in the smallest streamlets (in winter, 68.4% of the food). Otters also eat toads Bufo bufo. In some areas crayfish and mammals are quite important; but for most otters in the study area salmonids, birds, reptiles, insects, moliusks and plants are only occasional food. Most of the otters in the study area live in small forest rivers. In central Finland in winter amphibians and sculpins are of great importance for otters living in small rivers.
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