Oxygen equilibrium curves and other respiratory-related variables were determined on blood from the flatback turtle (Natator depressus) and, for comparison, on some samples from the loggerhead turtle (Caretta caretta). The oxygen carrying capacity of the flatback turtle, 4.9-8.7 mmol l(-1) (n = 49), is at the high end of the range in diving reptiles. Oxygen affinity (P(50)) was similar in both species at 5% CO(2), ranging from 37 to 55 mmHg (43 mmHg +/- 5.3 SD, n = 24, 25 degrees C, pH 7.17) in flatbacks and 43-49 mmHg in loggerheads (46 mmHg +/- 2.0 SD, n = 7, 25 degrees C, pH 7.13), whereas at 2% CO(2), flatbacks had a higher oxygen affinity. The curves differed in sigmoidicity, with Hill n coefficients of 2.8 and 1.9 in flatbacks and loggerheads, respectively. The Bohr effect was small in both the species, consistent with results from other sea turtles. Lactate levels were high, perhaps because the samples were taken from turtles coming ashore to lay eggs. Flatbacks are rarely found in waters deeper than 45 m. It is suggested that they have a respiratory physiology particularly suited to sustain prolonged shallow dives.
[Show abstract][Hide abstract] ABSTRACT: ABSTRACT: Marine turtle hatchlings emerge from nests on oceanic beaches, crawl to the surf zone
and migrate offshore. Predators in shallow water can take many hatchlings, but once the turtles reach
deeper water, both encounters with predators and mortality rates probably decline. Behavioral studies
have demonstrated that hatchlings show changes in swimming activity as they migrate offshore.
During the first 24 h of migration, most species swim continuously (the ‘frenzy’), thereby minimizing
their time in shallow waters; however, swimming activity later declines in duration and vigor, especially
at night (the ‘postfrenzy’). One interpretation of these differences is that hatchling migratory
behavior evolved in response to the threat of predators (the ‘predation risk’ hypothesis). To further
test this hypothesis, we quantified the daily swimming activity shown by the flatback Natator depressus,
the only marine turtle that lacks an oceanic phase in its development. Instead, the hatchlings
remain in relatively shallow Australian (continental shelf) waters where they may frequently
encounter predators. We speculated that because of these encounters, flatback hatchlings might
have evolved activity patterns that show little, if any, decline during migration. Over 4 d of laboratory
observations, flatback activity at night declined by <13%. Over the same time period, nocturnal
activity declined by 60 to 95% (depending on species) in other marine turtles with an oceanic phase
in their life history. Our data therefore support the hypothesis that predation played an important role
in shaping the evolution of hatchling migratory behavior, although they do not provide direct evidence
of a cause and effect relationship.
Endangered Species Research 11/2009; 9(1):41-47. DOI:10.3354/esr00233 · 2.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents the first data on the diving behaviour of Flatback turtles, Natator depressus, between nesting events. Dive profiles were recorded in turtles from breeding populations at Curtis island in Queensland and at Bare Sand Island in the Northern Territory, using Time-Depth Recorders (TDRs). Both populations displayed dive types typical of those described in other internesting sea turtles. Dives spent on the seabed were most prevalent, accounting for 57% of the time at depth.While on the sea bed, the turtles apparently remained inactive, cyclical changes In depth reflecting the tidal cycle.These inactive dives were long compared to those typical of other large sea turtles such as C. mydas and C. caretta, up to 98 min (mean 80 12 min), and with a mean and median of 50 and 52 min, respectively. In both populations, these dives occurred more commonly by day, by an average of 14%, and were most prevalent in the middle third of the internesting interval in most turtles, while the eggs were maturing.The turtles spent only 10% of their time at or near the surface and surface intervals rarely exceeded a few minutes, insufficient to be attributed to a need for either rest or thermoregulation. The Bare Sand Island population showed longer dive durations and proportionally more dives with a gradual ascent phase, a phase presumed to be a method of compensating for buoyancy loss and a way for turtles to conserve energy in mid-water while still moving around. Maximum dive depths of 29 m and 44 m were recorded at Curtis Island and Bare Sand Island respectively, probably reflecting differences In bathymetry.
Australian Zoologist 01/2010; 35(2). DOI:10.7882/AZ.2010.018
[Show abstract][Hide abstract] ABSTRACT: The flatback turtle is the only species of marine turtle that lacks an oceanic phase of development in its early life history. Instead, the turtles grow to maturity in shallow turbid shelf waters of tropical to subtropical Australia. We studied the development of diving behavior in neonate flatbacks to determine whether diving under those ecological conditions resulted in differences from leatherbacks (Dermochelys coriacea) and green turtles (Chelonia mydas) at the same age when diving in clear, deep oceanic waters. Data were obtained from flatbacks that varied in both age (1–7 weeks) and mass (38–100 g). Each turtle towed a miniature time–depth tag during a single 30-minute trial in shallow (≤ 12 m) turbid shelf waters near Townsville, Queensland, Australia. In total, 192 dives were recorded from 22 turtles from 4 nests. Most dives were short (< 100 seconds) and shallow (< 4 m), but even young turtles could dive to the bottom. The most common flatback dives had V- or W-profiles, whereas, in leatherbacks, most dives were V-profiles, and, in green turtles, the dives were either V- or U-profiles. Routine flatback dives were accomplished by swimming slowly (like leatherbacks), but, when sufficiently motivated, flatbacks could swim faster (> 1 m/s) than green turtles. They could also make repeated deep dives after surfacing only briefly to replenish their oxygen supply. Changes in performance (longer, shallower dives) were correlated with increases in mass but not age. We hypothesize that, as neonates, flatback dives enable the turtles to 1) search efficiently for prey throughout the water column under conditions of limited visibility, 2) minimize surface time so that even in murky water the turtles can return to previously attractive locations, and 3) swim rapidly to evade their predators.
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