A biphasic navigational strategy in loggerhead sea turtles

Abstract

The homing journeys of nine loggerhead turtles translocated from their nesting beach to offshore release sites, were reconstructed through Argos and GPS telemetry while their water-related orientation was simultaneously recorded at high temporal resolution by multi-sensor data loggers featuring a three-axis magnetic sensor. All turtles managed to return to the nesting beach area, although with indirect routes encompassing an initial straight leg not precisely oriented towards home, and a successive homebound segment carried out along the coast. Logger data revealed that, after an initial period of disorientation, turtles were able to precisely maintain a consistent direction for several hours while moving in the open sea, even during night-time. Their water-related headings were in accordance with the orientation of the resulting route, showing little or no effect of current drift. This study reveals a biphasic homing strategy of displaced turtles involving an initial orientation weakly related to home and a successive shift to coastal navigation, which is in line with the modern conceptual framework of animal migratory navigation as deriving from sequential mechanisms acting at different spatial scales.

Travel routes to remote ocean targets reveal the map sense resolution for a marine migrant

“…Turtles travelling to targets on mainland coasts may simply have to make the correct decision to turn left or right when reaching the coast and then can follow the shore to their destination [ 14 , 37 ]. In a similar way, migrating birds may reorientate homewards when they reach land after a sea crossing [ 28 ] and many terrestrial animals use visual landmarks to orientate [ 38 , 39 ].…”

Integrating Biologging and Behavioral State Modeling to Identify Cryptic Behaviors and Post-capture Recovery Processes: New Insights From a Threatened Marine Apex Predator

“…Our results indicate a period of consistent, immediate offshore dispersal in white sharks after release from capture, with most individuals relocating into continental shelf waters (≥40-60 m depth, ∼10-30 km offshore) within ∼6 h and remaining there for the duration of their deployments (up to 136.2 h). Although some animals can exhibit disorientation and reduced movement rates immediately following capture (e.g., Luschi et al, 2020), rapid post-release offshore movements, similar to our observations in white sharks, have also been described across a range of marine taxa (Gunn et al, 2003;Mangel et al, 2011;Afonso and Hazin, 2014;Barnes et al, 2016), and have been interpreted to be a "flight" response associated with capture stress (Lear and Whitney, 2016). Supporting this explanation, offshore dispersal of white sharks coincided with a period of faster tailbeats (i.e., rapid movement), which gradually slowed to a more constant average rate, indicating a population-level recovery period (return to "baseline" tailbeat signature) of 9.7 h. This pattern and rate of TBC recovery is similar to that identified for common blacktip sharks (Carcharhinus limbatus, 9 h; Whitney et al, 2016), but longer than for tiger sharks (Galeocerdo cuvier, 4 h; Andrzejaczek et al, 2019a), potentially suggesting lower sensitivity to capture in tiger sharks (consistent with Gallagher et al, 2014).…”

Corneal Penetration of Low-Dose Atropine Eye Drops

“…Another mechanism could be the interaction of atropine and dopamine release [ 8 ]. While proteomic studies in retinal cells are ongoing, treatment with atropine in humans was accompanied by an increase of choroidal thickness and abolished choroidal thinning due to hyperopic defocus [ 71 ]. This is reminiscent of very similar observations in animal models: muscarinic acetylcholine agonists cause choroidal thinning in chickens, whereas antagonists cause thickening [ 72 ].…”