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

Diet of the otter Lutra lutra in an almost pristine Portuguese river: seasonality and analysis of fish prey through scale and vertebrae keys and length relationships

The seasonal diet and size of fish prey of the otter Lutra lutra were studied in an almost pristine river of North Portugal (Paiva river) through the analysis of spraints collected during 1 year. To identify Iberian freshwater fish species (Salmo trutta, Micropterus salmoides, Lepomis gibbosus, Luciobarbus bocagei, Cyprinus carpio, Carassius auratus, Pseudochondrostoma polylepis, Achondrostoma arcasii, and Iberocypris alburnoides) consumed by the otter keys based on scales and vertebrae were first developed and tested. Both keys allowed identification of all fish species, although three Cyprinidae species could not be discriminated (P. polylepis, A. arcasii, and I. alburnoides). Regression equations were calculated to estimate the dimensions of preyed fish. Highly significant linear relationships were obtained for the standard length versus vertebrae measurements, for all fish species, except for C. carpio. Fish was the predominant prey category in autumn and winter, but the otter also preyed on amphibians, reptiles, mammals, and birds, particularly during spring and summer. In general, the otter consumed high proportions of small size fish (3–12 cm for the three indiscriminate Cyprinidae, 3–9 cm for C. carpio, and 6–12 cm for S. trutta).

Prey availability and diet of the Eurasian otter (Lutra lutra) on a large reservoir and associated tributaries

Eurasian otter, Lutra lutra (L., 1758), spraints collected at the Aguieira hydroelectric dam (central Portugal, n = 916) and tributaries (n = 412) were analysed to assess diet compared with prey availability. Fish and crayfish abundances in the reservoir were assessed with fyke and trammel nets. Prey availability in the tributaries was estimated by electrofishing. In both the reservoir and its tributaries, fish were the main prey and consisted predominantly of Lepomis gibbosus (L., 1758) (60%–65% of occurrences), which is an introduced species of Centrachidae that is abundant in the reservoir but is almost absent in the tributaries. These data suggest that otters using the tributaries feed predominantly in the reservoir. Seasonal dietary variations corresponded to increased availability of nonfish prey categories. Capture vs. consumption analyses demonstrated that otters did not consume L. gibbosus according to its availability. In fact, L. gibbosus was consumed less frequently when other prey species were more available (e.g., amphibians, eels, barbells). The tributaries offer important otter refuge areas that are scarce at the edge of the reservoir, and so, in large reservoirs care should be taken to minimize disturbance in the surrounding catchments. Results indicate that otter populations make use of these conjoint systems to ensure their survival.

Diet of European mink (Mustela lutreola) in Northern Spain

This study describes the diet of European mink (