Swimming ability in sea turtle hatchlings: a comparison between species

Abstract

After emerging from the nest, hatchling sea turtles leave their nests and head towards the surf. When reaching the water, they immediately engage in a frantic swim commonly known as the 'swimming frenzy', which lasts between 24 to 48 h. During this period, hatchlings rely solely on their yolk reserves as their energy supply to reach oceanic currents that will transport them to distant foraging grounds, where they remain until returning as immature sub-adults. Previous work has found that swimming effort of hatchling sea turtles during the swimming frenzy varies across species. However, detailed information about the changes in powerstroke and dogpaddling rates during the frenzy an energetic point of view, during the first crucial moments of their off-shore dispersal. I also established a cross-species comparison, in order to understand if differences in life history strategies contribute to the energetics of swimming of this phase. I found that aerobic metabolic rate and swim thrust in these three species decreased sharply during the first 2 hours of swimming, followed by a less sharp decrease until 12 hours. After 12h of swimming, swimming effort and oxygen consumption remained constant at lower levels until the end of the trial (18h). Overall oxygen consumption rates and thrust production was higher in green turtles, followed by loggerhead turtles with flatback turtles being the least vigorous swimmers. Although the same three-phase swimming pattern was identified in each species, flatback hatchling swimming effort decreased at a higher rate.Furthermore, the swimming efficiency of flatback hatchlings started decreasing after 6 hours of swimming, whereas it kept increasing in loggerhead and green turtle hatchlings.When analysing the factors that produce swim thrust in detail, green and loggerhead turtle hatchlings had similar power stroke rates and proportion of time spent power stroking, but the mean maximum thrust, and therefore overall thrust, was greater in green turtles.Flatback hatchlings, on the other hand, had overall lower values in all three components compared to green and loggerhead turtles, particularly in the proportion o f t i me spent power stroking. These results suggest that flatback turtles have a less intense swimming 3 frenzy, both in duration and distance of dispersal, which might be related to their restricted geographic distribution and to the absence of a pan-oceanic pelagic phase in their life cycle.The earliest stages of the frenzy swim are powered by both aerobic and anaerobic metabolic pathways. Analysis of changes in the concentration of blood lactate, glucose and corticosterone during the first four hours of swimming revealed a similar pattern in loggerhead and flatback turtle hatchlings. In these two species, blood lactate, glucose and corticosterone concentrations started high at crawling and progressively decreased over time. The pattern of green turtle hatchlings, however, appears to be different, with blood lactate and glucose concentrations peaking after 2 h of swimm...