Does behaviour affect the dispersal of flatback post-hatchlings in the Great Barrier Reef?

Abstract

The ability of individuals to actively control their movements, especially during the early life stages, can significantly influence the distribution of their population. Most marine turtle species develop oceanic foraging habitats during different life stages. However, flatback turtles (Natator depressus) are endemic to Australia and are the only marine turtle species with an exclusive neritic development. To explain the lack of oceanic dispersal of this species, we predicted the dispersal of post-hatchlings in the Great Barrier Reef (GBR), Australia, using oceanographic advection-dispersal models. We included directional swimming in our models and calibrated them against the observed distribution of post-hatchling and adult turtles. We simulated the dispersal of green and loggerhead turtles since they also breed in the same region. Our study suggests that the neritic distribution of flatback post-hatchlings is favoured by the inshore distribution of nesting beaches, the local water circulation and directional swimming during their early dispersal. This combination of factors is important because, under the conditions tested, if flatback post-hatchlings were entirely passively transported, they would be advected into oceanic habitats after 40 days. Our results reinforce the importance of oceanography and directional swimming in the early life stages and their influence on the distribution of a marine turtle species.

Artificial light disrupts the nearshore dispersal of neonate flatback turtles Natator depressus

“…This indicates that hatchlings were actively swimming in a constant heading offshore using a strategy known as 'full drift', where the animal maintains its constant heading regardless of the direction of flow (Chapman et al 2011). Directional swimming such as we observed in the nearshore zone has been suggested to be a strategy that helps flatback hatchlings remain in coastal waters, as it prevents them from being carried out to sea (Wildermann et al 2017). The nearshore dispersal pathways of turtle hatchlings are largely unknown and are therefore predicted using models (Hamann et al 2011, Wildermann et al 2017.…”

Turtles on the trash track: loggerhead turtles exposed to floating plastic in the Mediterranean Sea

“…The distribution of floating plastic items is predominantly driven by surface currents, whereas sea turtles can move independently of currents from very young ages (Bentivegna et al 2007, Putman & Mansfield 2015, Wildermann et al 2017). However, the distribution of macro-planktonic organisms, such as jellyfish and salps, the preferred prey on which turtles forage in the open sea, is also governed by currents, so it can be expected that there will always be zones of co-occurrence of marine debris and food for turtles, and hence, these zones will attract the turtles themselves.…”

“…According to Suaria & Aliani (2014), 62 million macro litter items are currently floating on the surface of the whole Mediterranean basin, temporarily accumulating in certain areas driven by ocean circulation dynamics and anthropogenic activities (Mansui et al 2015). Sea turtles can move independently of currents, even as hatchlings (Bentivegna et al 2007, Putman & Mansfield 2015, Wildermann et al 2017. Moreover, most of the preferred prey for sea turtles while they are in oceanic waters are macro-planktonic organisms, whose distribution is governed by currents.…”

Phylogeography, genetic stocks, and conservation implications for an Australian endemic marine turtle

“…Similar strong discontinuity of mtDNA haplotypes characterizes endemic Australian sea lions (Neophoca cinerea) that breed at isolated colonies along the south coast (Campbell, Gales, Lento, & Baker, 2008;Lowther, Harcourt, Goldsworthy, & Stow, 2012). This is thought to be driven by selective pressures for localized foraging strategies, whereas in marine turtles the selective pressures would target nest site selection in time and space, with a need for successful embryonic development and hatchling dispersal into coastal currents at appropriate times (Wildermann et al, 2017).…”