Post-nesting migrations of Galápagos green turtles Chelonia mydas in relation to oceanographic conditions: integrating satellite telemetry with remotely sensed ocean data

Abstract

Post-nesting movements of 12 green turtles from the Galápagos Islands (Ecuador) were tracked with satellite telemetry during the 2003 and 2005 nesting seasons. To illuminate potential environmental influences on turtle movements we compared tracks with a variety of remotely sensed oceanographic variables including sea surface temperature (SST), SST front probability, surface height anomaly, surface current, and surface chlorophyll a concentration. Three distinct post-nesting migratory strategies were observed, including oceanic migration to Central America (Type A1 movements, n = 3), residency within the Galápagos (Type A2 movements, n = 2), and movement into oceanic waters southwest of the Galápagos (Type B movements, n = 7). Two turtles migrating to Central America reached neritic foraging areas in Nicaragua and Panama that were 1500 and 1542 km, respectively, from their nesting sites, and one resident turtle established a foraging home range 75 km from its final nesting site. Oceanic movements occurred in waters with a mean SST of 26.5°C and mean surface chlorophyll a concentration of 0.18 mg m-3 , whereas neritic movements were in waters with a mean SST of 24.3°C and mean surface chlorophyll a concentration of 0.47 mg m-3. All turtles accessed SST frontal zones at a greater rate than their availability, and at least 2 turtles conducted movements in the oceanic zone that were indicative of foraging activity. This is the first report of migratory corridors for Galápagos green turtles, confirming prior flipper tagging data that show that the Galápagos is a source rookery for green turtles in coastal areas of Central America. The high proportion of green turtles departing the Galápagos (83%) indicates that marine fisheries bycatch and directed hunting on this stock outside the Galápagos may impact this population more than previously believed, and underscores the need for multinational conservation efforts that combat these threats.

A biologist’s guide to assessing ocean currents: a review

“…The effects of geostrophic currents (velocity and direction) on animal movements have been investigated in several marine species (e.g. Polovina et al 2000, Horrocks et al 2001, Ream et al 2005, Seminoff et al 2008, Godley et al 2010. However, the state-of-the art approach is now to estimate the effects of total surface currents on animal movements by combining both the mean and anomaly of the surface geos trophic flow and an inferred surface Ekman current (e.g.…”

“…Lagrangian drifter buoys (see Appendix 1) provide 'direct' in situ information on surface currents (Campagna et al 2006, Horton et al 2011, although there are caveats related to buoy performance. Two additional techniques are well established: (1) satellite observations are used to infer surface current fields at regular intervals (Gaspar et al 2006, Cotté et al 2007, Seminoff et al 2008, Bailleul et al 2010, Campbell et al 2010; and (2) particles are tracked in numerical ocean circulation models to mimic Lagrangian drifter buoys (Bonhommeau et al 2009, Sleeman et al 2010, Kobayashi & Cheng 2011. While surface currents may be estimated from satellite observations at a spatial resolution of about 25 to 100 km (Rio & Hernandez 2004, Pascual et al 2006, Rio et al 2011, the current fields simulated in ocean general circulation model (OGCM) hindcasts (e.g.…”

“…For instance, estimating the ocean currents along the paths of satellite-tracked marine species, such as sea turtles, sea birds or marine mammals, may allow inferences of how environmental factors contribute to the animal's movement and behaviour (e.g. Sakamoto et al 1997, Nichols et al 2000, Hatase et al 2002, Luschi et al 2003a, Gaspar et al 2006, Cotté et al 2007, Seminoff et al 2008, Bailleul et al 2010.…”

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…Papi et al 1997;Blumenthal et al 2006;Hawkes et al 2007;Girard et al 2009) and green turtles (e.g. Luschi et al 1996;Cheng 2000;Craig et al 2004;Seminoff et al 2008), as are the small-scale internesting movements performed by loggerheads, also typically recorded elsewhere (Stoneburner 1982;Limpus & Limpus 2001). Given that in the Mediterranean the largest Figure 6.…”

Green turtle population structure in the Pacific: new insights from single nucleotide polymorphisms and microsatellites

“…In the eastern tropical Pacific, however, satellite, tagging and genetic studies suggest mixing of animals from different nesting populations at foraging grounds (Green 1984, Amorocho et al 2012. Post-nesting migration of female green turtles from the Galapagos Islands included north-bound migration to Central America, residency in the Galapagos, and dispersal to oceanic waters southwest of Galapagos, illustrating the variability of migratory strategies to different foraging habitats within a single breeding population (Seminoff et al 2008). Although breeding is generally believed to occur adjacent to the nesting beaches when females are reproductively receptive, the overlapping foraging areas perhaps offer greater opportunity for a low level of male-mediated gene flow between Galapagos and Mexico than between Hawaii and the eastern Pacific rookeries, and should not be ruled out as a potential factor contributing to the lower differentiation.…”