Satellite tracking reveals unusual diving characteristics for a marine reptile, the olive ridley turtle Lepidochelys olivacea

Abstract

The movements, diving behaviour and thermal environment occupied by 4 adult female olive ridley turtles Lepidochelys olivacea in northern Australia were determined through satellite telemetry. Patterns of behaviour recorded were rather unusual compared to other sea turtles in that dives were mainly deep, largely benthic and exceptionally long (> 2 h) in some cases, characteristics typical of over-wintering turtles in colder environments. One individual occupied shallow coastal foraging zones, while the others foraged far from land (probably on the seabed) in relatively deep water (>100 m). Individuals performed long dives (frequently >100 min), but from the short post-dive intervals we suggest that these dives were mainly aerobic. Maximum dive depth recorded was 200 ± 20 m (mean maximum depths ranged from 20.1 to 46.7 m across individuals; n = 17 328 dives in total; depths ≥3 m were considered 'dives') and the maximum duration was 200 ± 20 min (mean durations ranged from 24.5 to 48.0 min across individuals). Temperature profiles indicate that turtles experienced temperatures ranging from 23 to 29°C at the surface, with the lowest temperature recorded (18.7°C) at a depth of 98 m. Only 6.9% of the dives were in water < 20°C. From time-allocation at depth (TAD) scores, we demonstrated that many dives reaching the known or inferred sea bottom were U-shaped, but there was no apparent diel signal in dive depth. This suggests that many benthic dives were not associated exclusively with resting behaviour and likely had a foraging component as well. The ability to perform long benthic dives allows this species to exploit deeper benthic environments in addition to the shallow coastal areas more generally occupied by adult hard-shelled sea turtles (e.g. green and hawksbill turtles). Deep benthic dives also occur in certain marine mammals (e.g. narwhals) and sea birds (e.g. rockhopper penguins) and therefore seem to be a general foraging strategy exploited by animals that can perform long dives.

A global review of marine turtle entanglement in anthropogenic debris: a baseline for further action

“…Firstly, this species, which often exhibits mass nesting in the hundreds of thousands of individuals, is highly numerous, and at particularly high densities in some areas, leading to entanglement hotspots (Jensen et al 2006, Koch et al 2006, Wallace et al 2010a). Secondly, the olive ridley forages along major oceanic fronts which are known to aggregate marine debris (Polovina et al 2004, McMahon et al 2007). Finally, their generalist feeding behaviour potentially attracts them to feed opportunistically on biofouled marine debris such as ghost gear (Stelfox et al 2016).…”

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

“…In most leatherback populations, females cover extensive areas between nesting events, though normally stay within the continental shelf (Eckert et al, 2006;Georges et al, 2007;Hitipeuw et al, 2007). Despite some loggerhead, olive ridley, and green sea turtle (Chelonia mydas) populations undertaking oceanic loops during internesting periods (Blumenthal et al, 2006;McMahon et al, 2007) and flatback sea turtles (Natator depressus) demonstrating variable behaviors in Western Australia (Waayers et al, 2011;Whittock et al, 2014), most hard shelled turtles tend to stay close to their nesting beaches (loggerheads: Godley et al, 2003;greens: Hays et al, 1999;Craig et al, 2004;Troëng et al, 2005;Fuller et al, 2008; Shaver and Rubio, 2008). This intense habitat use allows for more targeted conservation measures .…”

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

“…However, they have other biological characteristics such as low metabolism, narrow thermal niche and nesting dichotomy that may make them vulnerable to environmental change unless they are able to adapt on relevant time scales (Merchant-Larios et al, 1997;Lutz et al, 2003;Polovina et al, 2003;McMahon and Hays, 2006;Plotkin et al, 2012). Climate change may be particularly problematic for sea turtles given population sexratios are temperature-dependent, and they nest on beaches that may be impacted by sea level rise (Hawkes et al, 2009).…”

“…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.…”