Abstract
Quantifying early life movements is essential to understanding migratory pathways and habitat use that can impact individuals’ success later in life. To gauge how neonatal movements set the stage for later habitat use, we tracked neonate leatherback turtles (n=94) with acoustic tags from Pacuare, Costa Rica, in 2016 and 2018. We analyzed movements using a first passage time analysis and random walk models, the results of which indicated neonates followed a fixed compass direction as they traveled away from shore and that strong currents in these areas resulted in advection. We combined the tracking data with concurrent environmental variables in a generalized additive mixed model framework. Our results showed the south-east current flow in this area has spatial and temporal structure that was not driven by the tidal current or local wind speed. Accounting for advection by the currents, in-water neonate swimming speed was significantly related to current speed, first passage time, and the year. Neonates had three main response strategies to currents above 0.5 m s-1, with most increasing their swimming speed and the rest maintaining either a constant or decreased swimming speed. Neonates were significantly larger in 2018 than in 2016 but their average swimming speed was not significantly related to body size, indicating that environmental factors were more important contributors to their dispersal. We conclude that abiotic factors, including the strength and direction of the currents, significantly affect the swimming and dispersal strategy of neonate leatherback turtles and these results can help to inform strategies for releases of neonate turtles from hatcheries, future tracking studies, and conservation efforts.
Highlights
Advancements in biotelemetry have helped bridge the gap between animals’ fine and broad-scale movement patterns, opening up new opportunities for the movement ecology of different life stages to be quantified and understood (Nathan et al, 2008)
A total of 27 neonates tracked from hatchery nests and 15 from incubator-hatched eggs in 2016, and 33 neonates tracked from hatchery nests and 19 from incubator-hatched eggs in 2018
Drifters were deployed for the majority of neonate tracks (n = 76) to determine current speed and direction
Summary
Advancements in biotelemetry have helped bridge the gap between animals’ fine and broad-scale movement patterns, opening up new opportunities for the movement ecology of different life stages to be quantified and understood (Nathan et al, 2008). Satellite tags have become progressively smaller in size and capable of attachment to the larger juvenile life stages for animals such as birds, sharks, sea turtles, and marine mammals (Kjellén et al, 2001; Vincent et al, 2002; Hsu et al, 2007; Weng et al, 2007; Mansfield et al, 2014), their application on the much smaller, dispersing neonate phase is limited Tagging of this vulnerable life stage has most often been applied to the fledgling stage in birds (Hake et al, 2001; Hake et al, 2003; Kooyman and Ponganis, 2007; Cadahía et al, 2010; Péron and Grémillet, 2013; Vega et al, 2016). Characterizing this early life stage is important, as the movement and behavioral responses of neonates to different environmental conditions could potentially have carryover effects on the distribution, energetics, or survival of later life stages (O’Connor et al, 2014)
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