Predation of sea turtles (Chelonia mydas) by southern sea lions (Otaria byronia) and its relationship with overfishing in northern Chile

The disruption of a new food chain in the South American sea lion (SSL, Otaria byronia), with predation on green sea turtles (GST, Chelonia mydas) is reported for Northern Chile, probably from “nutritional stress” as result of anchovy (Engraulis ringens) overfishing, its fundamental food, with implications that cross multinational barriers in the South Pacific due to the shared nature of the resource. From 2011 an increase in carcasses of GST turtles with damages attributable to attacks by larger predators was observed on beaches of Arica (18°28´S), for which a necropsy study for signs attributable to predation, was carried out between November 2013 and May 2019. Jointly, direct observations of SSL attacks were made between Arica (18°28´S) and Iquique (20°13´S), that document predation of GST by SSL. 195 strandings including 179 Chelonia mydas, 15 Lepidochelys olivacea y 1 Eretmochelys imbricatea were recorded. 96.01% were strandings, 2.23% concentrated in drift, 1.12% as ghost fishing and 0.56% by fishermen from a gillnet. The necropsies of 14 carcasses in stage 1 and 2, showed damage attributable to interaction (alive or dead) with predators and/or scavengers. Most part of the observed injuries (tears of breakage and detachment of skin, muscles, internal structures such as the trachea, esophagus, stomach and part of the intestines, heart and liver) were attributable to SSL attacks and agree with the direct observations. Attacks by sharks or killer whales, and death by immersion or health problems could not be confirmed. The effect of this new feeding strategy of the SSL casts a shadow of uncertainty about the success of the green sea turtle population recovery program of northern Chile started in 2012. The results also suggest the need for evaluation of anchovy management programs and standards and the incorporation of an ecosystem approach to management plans, including the trophic needs of top depredators of the system.