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

Abstract

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.

A multi-scale analysis of the habitat associations of European otter and American mink and the implications for farm scale conservation schemes

“…Based on repeat site surveys, with an increase in a single positive site for both species, suggests a high level of confidence in the detection of positive rivers. Sales-Luís et al (2007) observed that otters feeding predominantly in a large reservoir also relied heavily on surrounding habitat refugia along tributaries. Therefore, in the present study within-farm scale variables may not be observed, as otter signs at a single point may reflect presence resulting from utilisation of other exploitable areas.…”

Diet analysis of the African clawless otter (Aonyx capensis) in and around Lake Tana

“…The diet of the African clawless otter like other species of small-clawed otters (Kanchanasaka and Duplaix, 2011), spotted-necked otter (Perrin and Carugati, 2000), European otter (Sales-Luis et al, 2007) and the American river otter (Melissa, 2006) showed a seasonal variation in its diet. The high percentage occurrence of fish in the wet season diet of the African clawless otter may be explained by the spawning migration behaviour for reproduction in their breeding sites to the rivers and shores.…”

The Eurasian otter Lutra lutra (Linnaeus, 1758) in Portugal

“…As a result, otters were found to be frequent in most Portuguese rivers, although, lacking a standardised monitoring protocol, data were mostly scattered over space and time (Ferrand-Almeida, 1980;Macdonald & Mason, 1982;Santos-Reis, 1983;Simões-Graça & Ferrand-Almeida, 1983;Trindade, 1987Trindade, , 1989Trindade, , 1991Beja, 1989a, b). Basto et al, 2011), large dams (Pedroso, 1997(Pedroso, , 2012Pedroso & Santos-Reis, 2006, 2009Pedroso et al, 2007;Sales-Luís et al, 2007;Santos et al, 2008;Pedroso, 2012;Pedroso et al, 2013), estuaries (Campos, 1993;Trigo, 1994;Trindade, 1996;Freitas et al, 2007;SalesLuís et al, 2009;Sales-Luís, 2011) and sea coast environments (Beja, 1989a;Beja, 1992;Gomes, 1998;Pedrosa, 2000;Cerqueira, 2005).…”

“…Gomes et al, 1989;Beja,1989aBeja, ,1991Beja, ,1995aBeja, ,b,1996aFlorêncio, 1993Florêncio, , 1994Trigo, 1994;Gomes, 1998;Farinha, 1995;Sousa, 1995;Chambel, 1997a,b;Pedroso, 1997;Azinheira, 1998;Freitas, 1999;Lopes, 1999;Matos, 1999;Silva, 1999;Pedrosa, 2000;Barrinha, 2002;Magalhães et al, 2002;Trindade, 2002;Garcia, 2005;Novais, 2005;Pedroso & Santos-Reis, 2006;Freitas et al, 2007;Marques et al, 2007;Sales-Luís et al, 2007;Marques, 2010;Basto et al, 2011;Pedroso et al, 2013). Hence the otter diet in the different Portuguese aquatic habitats is currently well known.…”

“…Such a feeding adaptability suggests that the otter is better described as an opportunist predator rather than as a specialist (e.g. Sales-Luís et al, 2007).…”