Ghost Nets Haunt the Olive Ridley Turtle (Lepidochelys olivacea) near the Brazilian Islands of Fernando de Noronha and Atol das Rocas

Abstract

Fernando de Noronha (3.8333°S, 32.4167°W) and Atol das Rocas (3.8666°S, 33.8000°W) are Brazilian offshore islands that host breeding populations of Green Turtles (Chelonia mydas) and provide benthic foraging habitat for aggregations of Green and Hawksbill Turtles (Eretmochelys imbricata; Marcovaldi and Marcovaldi 1999) and occasionally Loggerheads (Caretta caretta; Bellini and Sanches 1998). The fact that Olive Ridley Turtles (Lepidochelys olivacea) also forage in the vicinity of these offshore islands is evidenced by carcasses found stranded on the beach and animals entangled in ghost nets, i.e., abandoned, lost, or otherwise discarded fishing gear. From 1996 to 2011, 20 Olive Ridley Turtles were recorded by the Brazilian sea turtle conservation program (Projeto TAMARICMBio), including 17 at Fernando de Noronha and 3 at Atol das Rocas. Of these, 18 were entangled in ghost nets (16 still alive and 2 dead) and another two individuals were found dead, stranded on the beach. The three turtles recorded at Atol das Rocas were alive and entangled together in the same ghost net, as were four turtles at Fernando de Noronha; all other entanglements were of single individuals. All the nets consisted of multifilament nylon, with mesh sizes of 17–22 cm (stretched mesh). The origin of these nets is unknown, neither is it clear if the nets were used in high seas or coastal fisheries or by national or international ships. Indeed, neither the scale nor magnitude of fishing activity (industrial or artisanal) in the area, or the target species, have yet been determined. Ghost nets are a well-documented threat for marine fauna including sea turtles (Halpern et al. 2008; Macfadyen et al. 2009). In spite of the fact that the origin of the ghost nets is unknown, the influence of the ocean currents seems to be clear. Atol das Rocas and Fernando de Noronha are located where the South Equatorial Current (SEC) flows from east to west (Kikuchi 2000; Renner 2004) and all recorded entanglement was east of the islands. This could indicate that ghost nets were upstream of the location where the turtles were found.