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Diet composition of otters (Lutra lutra) was investigated in 2001 by spraints analysis (N ¼ 1323) on five rivers of southern Italy, with the aim of assessing the influence of fish availability, elevation and discharge on the consumption of food resources alternative to fish. Data were expressed as per cent frequency of occurrence (%FO) and per cent volume (%V). The study confirmed the great feeding adaptability of the otter that, in rivers partially interconnected and flowing on a small area, showed a strong fish eating habit in some rivers (Sinni and Mercure-Lao) and a diet mainly constituted by alternative resources in other ones (amphibians in the rivers Cogliandrino and Frido, crustaceans in the River Battendiero). Fish consumption for the five rivers was significantly correlated with fish biomass and with mean summer discharge, while it was inversely correlated with the mean altitude of the five rivers. The lack of a clear seasonality in the consumption of food sources alternative to fish together with the correlation between fish use and fish biomass for each river indicated fish availability as the main factor affecting otter relying to non-fish preys. Otter diet seemed influenced by the characteristics of river habitats (altitude, discharge and consequently fish biomass) more than by summer drought, typical of Mediterranean regions. The %FO and the %V allowed to drawn a similar picture of otter diet. Nonetheless the %V was useful for better illustrating diet variation among the different rivers and we argue that it could be useful in habitats where the otter feeds on preys with different proportions of indigestible remains.

In 2001 and 2002 we studied Eurasian otter (Lutra lutra) fish selection in southern Italy by comparing otter diet (805 analysed spraints) with fish availability, estimated by electrofishing. The surveyed river was dominated by cyprinids, particularly by chub (Leuciscus cephalus), roach (Rutilus rubilio) and bleak (Alburnus sp.). Roach and chub were the most common prey recorded in spraints. Otters ate mainly small prey (total length < 90 mm). Chub were widely consumed according to abundance, whilst roach and bleak consumption was not proportionate to their availability. Otters selected roach both in 2001 and 2002 and responded to a decrease in roach availability (-27.3%) by increasing their frequency of consumption rather than switching to an alternative prey. Despite their high abundance, bleak seemed to be markedly avoided by otters. We hypothesized that differences in microhabitat selection may influence the susceptibility of cyprinids to otter predation. The possible effects on fish community were briefly discussed.

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