ORIGINAL PAPER Trophic interactions of the endangered Southern river otter (Lontra provocax) in a Chilean Ramsar wetland inferred from prey sampling, fecal analysis, and stable isotopes Marcela Franco & Giovany Guevara & Loreto Correa & Mauricio Soto-Gamboa Received: 31 May 2012 / Revised: 16 February 2013 / Accepted: 20 February 2013 / Published online: 7 March 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract Non-invasive methodological approaches are highly recommended and commonly used to study the feed- ing ecology of elusive and threatened mammals. In this study, we use multiple lines of evidence to assess the feed- ing strategies of the endangered Southern river otter, by determining seasonal prey availability (electrofishing), anal- ysis of undigested prey remains (spraints), and the use of stable isotopes (δ 15 N and δ 13 C) in otter spraints (n =262) and prey in a wetland ecosystem of southern Chile (39°49′S, 73°15′W). Fecal and isotopic analyses suggest that the otter diet is restricted to a few prey items, particularly the less- mobile, bottom-living, and larger prey such as crayfish (Samastacus spinifrons, 86.11 %) and crabs (Aegla spp., 32.45 %), supplemented opportunistically by cyprinids ( Cyprinus carpio, 9.55 %) and catfish ( Diplomystes camposensis, 5.66 %). The results suggest that the river otter is highly specialized in bottom foraging. Isotopic sig- natures of food sources and feces revealed a mid-upper trophic position for the Southern river otter, with either higher or lower δ 15 N values than their potential prey items. δ 13 C values for river otters were less enriched than their potential food resources. We suggest that due to their narrow trophic niche and possible dependence on only a few food items, this species may be highly vulnerable to the reduction in its prey populations. Finally, maintaining the ecological interactions between Southern river otters and their prey is considered a central priority for the survival of this endan- gered carnivore mammal. Keywords Southern river otter . Stable isotopes . Trophic ecology . Wetland . Chilean freshwater Introduction The Southern river otter, or huillín (Lontra provocax Thomas, 1908), is one of four South American otter species and is endemic to the Southern cone (Sielfeld 1983). This species is associated with freshwater ecosystems in the northern portions of its range (39°S), but further south, it inhabits the rocky seashores of the Patagonian archipelagos (Gomez et al. 2010). Populations started to originally de- cline due to high hunting pressure and, despite recent hunt- ing bans (Aued et al. 2003), this semi-aquatic species remains classified as “endangered” on the IUCN Red List of Threatened Species (Sepúlveda et al. 2008). This is because the riparian forest is seriously threatened by a number of factors, particularly by habitat destruction and increasing river channelization, which has prevented recov- ery and has caused further declines in populations of this species (Cassini et al. 2010; Medina-Vogel et al. 2003). As with other freshwater otters, this species is difficult to ob- serve in nature and is the reason why previous studies have relied upon direct as well as indirect methods to estimate distribution, population size, and conservation status (Sepúlveda et al. 2007, 2009; Cassini et al. 2010). L. provocax is an opportunistic predator that spends a great deal of its time budget searching and capturing prey (Reyes-Küppers 2007). Its diet has been studied mainly Communicated by: Sven Thatje M. Franco (*) : L. Correa : M. Soto-Gamboa Instituto de Ciencias Ambientales y Evolutivas, Facultad de Ciencias, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile e-mail: lidamarcelafranco@gmail.com G. Guevara Departamento de Desarrollo Rural y Recursos Naturales, Facultad de Ciencias Agropecuariass, Universidad de Caldas, Manizales, Colombia Naturwissenschaften (2013) 100:299–310 DOI 10.1007/s00114-013-1027-4