Migration routes and foraging behaviour of olive ridley turtlesLepidochelys olivaceain northern Australia

Abstract

The foraging ecology of endangered olive ridley Lepidochelys olivacea sea turtles is poorly known in Australia, with only a limited knowledge of their foraging distribution inferred from captures in trawl net fisheries. We attached satellite transmitters to 8 olive ridley turtles in 2004 and 2005 at a nesting beach in Australia's Northern Territory to document their migratory routes and foraging behaviour. Three turtles moved up to 40 km from the nesting beach before renesting on the same beach within 12 to 23 d. The turtles made post-nesting migrations of 165 to 1050 km to 5 different foraging areas and used coastal, continental shelf and continental slope habitats. The use of one foraging area by 3 turtles, together with previous trawl data, indicate a predictable source of food in this area. Distinct foraging areas indicate that foraging behaviour differs from the meandering oceanic movements of turtles in the Pacific. During migration and foraging periods, turtles dived to the substrate with maximum depths of 150 to 200 m and maximum dive durations of 120 to 180 min. The locations of foraging areas overlapped with existing trawl fisheries and oil and gas exploration and mining.

Opportunism on the High Seas: Foraging Ecology of Olive Ridley Turtles in the Eastern Pacific Ocean

“…While individuals have the ability to migrate >1,500 km, as nomads they do not have consistent home ranges (Pandav and Choudhury, 1998;Polovina et al, 2003;Whiting et al, 2007;Plotkin, 2010). Rather, they continuously forage opportunistically on a wide variety of prey.…”

“…They range >3 million km 2 across this dynamic ocean basin and are thus present in multiple biogeographic regions (Pennington et al, 2006;Olson et al, 2010;Plotkin, 2010). As nomadic opportunistic omnivores, they don't undergo ontogenetic habitat shifts and may feed in both benthic and pelagic habitats (Bjorndal, 1997;NMFS and USFWS, 1998;Robins et al, 2002;Bolten, 2003;Whiting et al, 2007;Behera et al, 2015). Olive ridleys often forage via passive drifting rather than active swimming, meaning they eat within the same food web for many days (Block et al, 2002;Polovina et al, 2003;McMahon et al, 2007;Whiting et al, 2007;Plotkin, 2010).…”

“…As nomadic opportunistic omnivores, they don't undergo ontogenetic habitat shifts and may feed in both benthic and pelagic habitats (Bjorndal, 1997;NMFS and USFWS, 1998;Robins et al, 2002;Bolten, 2003;Whiting et al, 2007;Behera et al, 2015). Olive ridleys often forage via passive drifting rather than active swimming, meaning they eat within the same food web for many days (Block et al, 2002;Polovina et al, 2003;McMahon et al, 2007;Whiting et al, 2007;Plotkin, 2010). Their oceanic diet consists of mostly planktonic items or items living on or near flotsam including algae, crustaceans, and salps (Kopitsky et al, 2005;Jones and Seminoff, 2013;Wedemeyer-Strombel et al, 2015;Pitman, Kopitsky and Peavey, pers.…”

Informing Marine Protected Area Designation and Management for Nesting Olive Ridley Sea Turtles Using Satellite Tracking

“…Green sea turtles nesting in French Guiana similarly used the Maroni River Estuary during their internesting period (Chambault et al, 2016) but additional occurrences are not known. In the Indian Ocean, female olive ridley turtles tagged on nesting beaches in Oman display consistent coastal use (Rees et al, 2012) but other populations of olive ridley turtles have been seen to move to offshore waters adjacent to the nesting beaches or immediately end the internesting period after their last nesting event and migrate toward foraging grounds (Whiting et al, 2007;Maxwell et al, 2011;Plot et al, 2015).…”

“…Therefore, they remain in the vicinity of nesting beaches for several weeks at a time (Whiting et al, 2007;Hamel et al, 2008;da Silva et al, 2011;Maxwell et al, 2011), termed the internesting period, during which they are susceptible to additional anthropogenic impacts (Pikesley et al, 2013a). This period also makes sea turtles ideal candidates for conservation measures because both sexes congregate in the same waters to breed and females typically return to the same beaches to nest multiple times in the same season (Van Buskirk and Crowder, 1994).…”