The diet of otters was studied by the means of spraint analysis in the Bieszczady Mountains, in southeastern Poland. The study area extended over 25 km long stretch of the River San, about 1 km above Solina dam reservoir. Spraints were collected on seven 2 km long sections in 1993, and on three sections in 2010. In both study periods, otter spraints were collected in August, when the weather conditions were similar. The study revealed high contribution of mountain fish species such as Phoxinus phoxinus,Cottus spp., and Barbatula barbatula in otter diet. Diet composition along the River San showed little variation in 1993, except from the section closest to dam reservoir where it was characterised by the highest frequency of occurrence of perch Perca fluviatilis, cyprinids and amphibians. The share of perch in otter diet decreased, while that of noble crayfish Astacus astacus increased with the distance from Solina reservoir.
Changes in otter diet between 1993-2010 were characterized by an increase of the consumption of perch and cyprinids on the one hand,
and a decrease of the consumption of crayfish, on the other. Both spatial and temporal changes in otter diet reflected the effect of Solina
reservoir on the river community and the availability of prey to otters. The results indicate the ongoing changes in fish community influenced by the construction of Solina reservoir.
Analysis of the stomach contents of otters recovered from South West England between 1999 and 2003 revealed that prey items taken were principally species of fish and amphibians, with mammals and birds occasionally taken. The fork length of fish recorded was 30 to 720 mm. Eel Anguilla anguilla was the dominant prey item, with up to five present per stomach. Estimated lengths ranged from 100 to 450 mm. Other common prey items were bullhead Cottus gobio and brown trout Salmo trutta. In addition to these freshwater species, there were recordings of sea bass Dicentrarchus labrax and thick lipped mullet Chelon labosus, indicating foraging in both freshwater and marine habitats. A seasonal peak was observed in the relative frequency of amphibians in diet, as otters took advantage of spawning aggregations. However, there were no seasonal trends in the relative frequency of other species in otter diet, with eel, bullhead and cyprinid species taken regularly in all months.