Anthropogenically altered trophic webs: alien catfish and microplastics in the diet of Eurasian otters

With the aim of examining how Eurasian otters (Lutra lutra) face human-mediated environmental alterations, we assessed their diet by spraint analysis on the River Ticino (NW Italy), where this mustelid has been reintroduced in 1997. From March 2016 to March 2017, a total of 101 spraints was found in 50% of 32 sampling stations (mean length ± SD = 567 ± 263 m). Fish formed the bulk of otter diet (95% of the estimated mean percent volume, mV%). Cyprinids were the most preyed fish (mV% = 44.9), followed by European catfish Silurus glanis (mV% = 24.9%) and eel Anguilla anguilla (mV% = 8.5). Introduced European catfish is an invasive species, which can deeply alter the composition and structure of local fish communities and accumulate large amounts of metals and pollutants through the trophic chain. We also recorded for the first time microplastic particles (< 5 mm) in otter spraints. Suspected particles were analysed by Fourier transform infrared (FTIR) spectroscopy and two polymer types were identified: polyethylene terephthalate (PET) and polyamide (PA). Although otters showed to be able to adapt to anthropogenic changes, these results point out new potential threats to otter conservation and ask for further studies.