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Leatherbacks are commonly found in Uruguayan waters (Fallabrino et al. 2000), although the nesting population sources of these leatherbacks are unknown. In Uruguay, the artisanal coastal gillnet fishery, the coastal bottom trawl fishery and the pelagic longline fishery are known to interact with leatherback turtles (Domingo et al. 2003; Fallabrino et al. in press; Miller et al. in press b). Leatherback turtles have been reported in interactions with the lines of crab or lobster traps, mainly in the US (Lewis, pers. com.; Lutcavage et al. 2001) and in Great Britain (Penhallurick 1991). Here, we present the first report of leatherback entanglement in trap lines in the Southwestern Atlantic Ocean.

The information was collected during an exploratory fishing trip (May 18 to June 17 2004), directed to catch molluscs (Zidona dufresnei and Tonna galea) using traps, by a scientific onboard observer from the National Direction of Aquatic Resources (DINARA). The activities carried out by the observer included gathering information on the fishing effort, describing the fishing gear and maneuvers, identifying target and bycatch species; and collecting physical (i.e salinity, surface temperature), biological and biometrics samples. The boat remained over the Uruguayan continental shelf, which is influenced by the presence of the subtropical convergence and the input of the Río de la Plata estuary (Figure 1). These features generate great spatio-temporal variability of environmental conditions. Variations include water temperature and salinity gradients throughout the year, with cold water coming from the South (Malvinas Current), and warm water coming from the North (Brazil Current) (Acha et al. 2004; Framiñan & Brown 1996, Severova & Severov 1996).

The fishing gear consisted of a polyamide mainline of 24 mm diameter and 1500 m length. At intervals of 10 m, 150 secondary lines of 3 fathoms were branched from the mainline, each one supporting a conical trap (3 kg) containing the bait and positioned on the sea bottom (Figure 2). The baits used were squid (Illex argentinus) alternated with anchovy (Engraulis anchoita), argentine hake (Merluccius hubbsi) and blue mussel (Mytilus edulis platensis). Each fishing set consisted of setting 14 polyamide mainlines, with soak time being 24 hours. The set velocity varied around 3 knots. Haul-back occurred at the end of the set with a hauling machine pulling the traps at high speed.

In May 2004, the observer recorded the incidental capture of 3 leatherback turtles, all of which were entangled in the front flipper with the mainline of the fishing gear. The sets which captured the turtles occurred at depths between 62 m and 75 m on the Uruguayan continental shelf (Figure 1 and Table 1). The first two turtles were disentangled and released alive by the observer with the help of the crew, but the third was already dead when haul-back occurred. Coincidently, the 3 incidental captures occurred while using anchovy and argentine hake as bait. The mainline may have drifted at least 2 m or 3 m off the bottom because of the length of the secondary lines. The mainline and the traps may not have remained on the bottom for the entire set, as they may have been lifted by currents in the area. It is unknown whether the turtles were caught while the fishing gear was resting at the bottom or while it was being hauled onboard. At this time, we cannot determine whether the fishing gear somehow attracted the leatherbacks turtles.

The closest large leatherback nesting beaches to the Southwestern Atlantic Ocean are in French Guiana and Gabon, although a relatively small nesting population occurs in Espírito Santo, Brazil (Barata et al. 2004). Recent incidental captures in Southern Brazilian and Argentinean waters of adult leatherbacks with metal Inconel tags from Gabon (Billes et al. 2006) suggest that the Uruguayan continental shelf might be used by leatherback turtles as a migratory corridor as well as a feeding area. Considering the conservation status of leatherback turtles and the lack of knowledge relative to its presence on the Uruguayan continental shelf, it is extremely urgent to direct more efforts to determine the spatio-temporal distribution of this species in Southwestern Atlantic Ocean waters. Further research and monitoring of the fisheries operating in this area is recommended in collaboration with corresponding governmental agencies and fishermen in order to have a better understanding of the occurrence of leatherback turtles and the magnitude of the incidental capture problem.

Acknowledgements: Thanks to the fishing crew, BP Conservation Programme, Birdlife International, Flora & Fauna International, Wildlife Conservation Society, Conservation International, NFWF, DINARA Scientific Onboard Observer Program, Andrés Domingo, Matthew Godfrey and two anonymous reviewers for their useful comments.

Table 1. Fishing effort data for the incidental capture of leatherbacks.

Figure 1. Map of the study area in the Southwestern Atlantic Ocean, showing the bathymetry and the incidental capture positions of the leatherbacks (black spots).

Figure 2. Fishing gear design used to trap snails. By- Buoy, ByL- Buoy Line, T- Trap, ML- Main Line, W-weight.

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