Eurasian otter Lutra lutra diet mirrors the decline of native fish assemblages in a semi-arid catchment (River Segura, SE Spain)

Abstract

In semi-arid environments, the effects of irregularly distributed rainfall, flow regulation and water inter-basin transfer enhance the spread of non-native fish to the detriment of native communities. In the River Segura, since the 1980s the number of non-native fish species has progressively increased, also because of the building of water transfer facility connecting the rivers Segura and Tajo. With the aim of highlighting how man-driven changes in the diversity of fish communities affect the diet of top-predators, we compared Eurasian otter Lutra lutra diet in the span of 20 years, i.e. 1997–98 vs. 2016–19. As habitat quality affects the condition of Andalusian barbel Luciobarbus sclateri, the most widespread native fish, we also compared the size of preyed barbels to point out whether human activities may have lowered their profitability to otters. Fish and introduced red swamp crayfish Procambarus clarkii formed the bulk of otter diet in both study periods. In 2016–19 the contribution of non-native species to otter diet increased significantly, both for crayfish and fish, which included ten non-native species. Otter feeding habits faithfully mirrored the variation in the composition of the fish community and confirmed the importance of crayfish as alternative-to-fish prey in the Iberian Peninsula. The average length of preyed barbels was significantly lower in the second study period, consistently with a decline in barbel profitability for otters.

Diet of the Otter Lutra lutra inhabiting a forest stream in SW Poland

“…It has been shown that the otter diet is more diverse in less stable environment, where non-sh prey are more often preyed upon (Ruiz-Olmo and Jimenez 2009; Dettori et al 2022). In our study, as in many other European habitats, alternative vertebrate prey other than amphibians, played a little role.…”

Eurasian otterLutra lutradistribution and habitat use in a Mediterranean catchment managed for the control of invasive giant reedArundo donax

“…Despite being strictly linked to aquatic habitats, otters may also benefit from well-preserved riparian forests, which may offer suitable resting sites especially in human-disturbed areas (Weinberger et al, 2019). Lack of riparian forest (Karr and Schlosser, 1978;Jones et al, 1999;Gregory et al, 1991), as so as water pollution (Changeux and Pont, 1995;Vila-Gispert et al, 2002), may also alter the abundance and distribution of fish, otters' main food resource (Dettori et al, 2022), affecting the use by otters of deforested stretches.…”