Open-Sea Migration of Magnetically Disturbed Sea Turtles

Abstract

Green turtles (Chelonia mydas) that shuttle between their Brazilian feeding grounds and nesting beaches at Ascension Island in the middle of the Atlantic Ocean are a paradigmatic case of long-distance oceanic migrants. It has been suggested that they calculate their position and the direction of their target areas by using the inclination and intensity of the earth's magnetic field. To test this hypothesis, we tracked, by satellite, green turtles during their postnesting migration from Ascension Island to the Brazilian coast more than 2000 km away. Seven turtles were each fitted with six powerful static magnets attached in such a way as to produce variable artificial fields around the turtle that made reliance on a geomagnetic map impossible. The reconstructed courses were very similar to those of eight turtles without magnets that were tracked over the same period and in the previous year, and no differences between magnetically disrupted and untreated turtles were found as regards navigational performance and course straightness. These findings show that magnetic cues are not essential to turtles making the return trip to the Brazilian coast. The navigational mechanisms used by these turtles remain enigmatic.

Green Turtles Highlight Connectivity Across a Regional Marine Protected Area Network in West Africa

“…Turtles passed through several RAMPAO MPAs during the migration period, but overall, MPA during migration was relatively low (21%), with a large portion of coverage provided by the Orango National Park (ONP), located near the nesting islands in the Bijagoś. Most turtles followed a similar path after leaving the nesting grounds potentially because they are using the same local environmental cues, such as ocean currents (Hays et al, 2010), wave-direction (Papi et al, 2000) or coastlines (Lohmann et al, 2008), to orient themselves. Yet some individuals diverted this corridor, and other populations display highly dispersed post-nesting migratory paths (e.g.…”

Nest-site choice by loggerhead sea turtles as a risk-management adaptation to offset hatching failure by unpredictable storms and predators

“…How do females manage to prevent future nest sites from overlapping too much with nest sites from current or previous breeding seasons? Recent studies show that geomagnetic navigational signatures and local cues such as wind currents, tidal currents, taste, and smell are imprinted in the brains of hatchlings and might continue to be imprinted on the brains of juveniles and adults as they migrate to and from foraging and breeding areas (Papi et al, 2000;Lohmann et al, 2008aLohmann et al, ,b, 2017Brothers and Lohmann, 2015;Kishkinev, 2015;Lohmann and Lohmann, 2019). The frontal brain of migratory sea turtles (i.e., the medial cortex) plays a key role in spatial cognition without extensive training (Striedter, 2016;Reiter et al, 2017).…”