Multinational Tagging Efforts Illustrate Regional Scale of Distribution and Threats for East Pacific Green Turtles (Chelonia mydas agassizii)

Abstract

To further describe movement patterns and distribution of East Pacific green turtles (Chelonia mydas agassizii) and to determine threat levels for this species within the Eastern Pacific. In order to do this we combined published data from existing flipper tagging and early satellite tracking studies with data from an additional 12 satellite tracked green turtles (1996-2006). Three of these were tracked from their foraging grounds in the Gulf of California along the east coast of the Baja California peninsula to their breeding grounds in Michoacán (1337-2928 km). In addition, three post-nesting females were satellite tracked from Colola beach, Michoacán to their foraging grounds in southern Mexico and Central America (941.3-3020 km). A further six turtles were tracked in the Gulf of California within their foraging grounds giving insights into the scale of ranging behaviour. Turtles undertaking long-distance migrations showed a tendency to follow the coastline. Turtles tracked within foraging grounds showed that foraging individuals typically ranged up to 691.6 km (maximum) from release site location. Additionally, we carried out threat analysis (using the cumulative global human impact in the Eastern Pacific) clustering pre-existing satellite tracking studies from Galapagos, Costa Rica, and data obtained from this study; this indicated that turtles foraging and nesting in Central American waters are subject to the highest anthropogenic impact. Considering that turtles from all three rookeries were found to migrate towards Central America, it is highly important to implement conservation plans in Central American coastal areas to ensure the survival of the remaining green turtles in the Eastern Pacific. Finally, by combining satellite tracking data from this and previous studies, and data of tag returns we created the best available distributional patterns for this particular sea turtle species, which emphasized that conservation measures in key areas may have positive consequences on a regional scale.

Distribution, size range and growth rates of hawksbill turtles at a major foraging ground in the eastern Pacific Ocean

“…Although satellite tracking has gained considerable attention over the last decade to determine marine turtle residency and habitat use, flipper tagging remains a more financially feasible tool for monitoring multiple individuals of a population and can provide data una- ttainable via satellite technologies (Hart et al, 2015). For eastern Pacific hawksbills, flipper tagging is particularly useful for population monitoring due to their small home ranges (Gaos et al, 2012a) and this is supported by our study, where all but one of the recaptured individuals were recaptured at their original capture site.…”

Assortative epibiosis of leatherback, olive ridley and green sea turtles in the Eastern Tropical Pacific

“…The similarity between the epibiont communities of distantly nesting conspecifics suggests that these individuals may share behaviours or biotic traits that are important for determining epibiont community structure. As sea turtles can migrate thousands of km between nesting and foraging areas, even distantly nesting conspecifics can still share foraging habitats (Bailey et al , 2012; Hart et al , 2015). Thus, as olive ridley turtles share both oceanic foraging habitats with leatherback turtles and coastal foraging habitats with green turtles, it would be expected for them to have intermediary epibiont communities between leatherback and green turtles.…”

“…Consequently, olive ridley turtles have been recorded inhabiting both oceanic and coastal waters depending on inter-annual patterns in food availability (Plotkin, 2010). Lastly, East Pacific green turtles (referred to subsequently only as green turtles), which are primarily herbivorous (Seminoff et al , 2002; Amorocho & Reina, 2007), forage in shallow coastal habitats, such as gulfs or estuary mouths (Blanco et al , 2012; Hart et al, 2015; P. Santidrián Tomillo & N.J. Robinson, unpublished data).…”

Assessing the exposure of animals to acoustic disturbance: Towards an understanding of the population consequences of disturbance

“…While we are not aware of similar analysis having been carried out with other marine species, the approach described here can be applied to any animal whose movements can be tracked. New tag technologies and attachment methods are making it possible to collect high quality tracking data for extended periods of time from a variety of marine vertebrates (Andrews et al, 2008;Block et al, 2011;Hammerschlag et al, 2011;Maxwell et al, 2013;Schorr et al, 2014;Hart et al, 2015;Block et al, 2016). Additionally, the incorporation of dive data along with tracking data provides a more robust data set to develop time-activity budgets that allow considerable insight into the behavior and energetics of these animals in general and their potential response to disturbance in particular (Mate, 2012;Del Raye et al, 2013;Naito et al, 2013;Whitlock et al, 2013;Jorgensen et al, 2015;Whitlock et al, 2015).…”