Complexity and variation in loggerhead sea turtle life history

Abstract

Juvenile loggerhead sea turtles spend more than a decade in the open ocean before returning to neritic waters to mature and reproduce. It has been assumed that this transition from an oceanic to neritic existence is a discrete ontogenetic niche shift. We tested this hypothesis by tracking the movements of large juveniles collected in a neritic foraging ground in North Carolina, USA. Our work shows that the shift from the oceanic to neritic waters is both complex and reversible; some individuals move back into coastal waters and then return to the open ocean for reasons that are still unclear, sometimes for multiple years. These findings have important consequences for efforts to protect these threatened marine reptiles from mortality in both coastal and open-ocean fisheries.

Sea Turtles in Florida's Atlantic Waters

“…These waters provide important developmental habitats for juvenile loggerheads originating from Florida, Mexico, the U.S. eastern seaboard, and other Atlantic nesting beaches (Witzell et al, 2002). Additionally, waters along the east coast of Florida provide seasonal overwintering habitats and year-round foraging grounds for loggerhead turtles (Henwood, 1987;Keinath, 1993;Ehrhart et al, 2007;McClellan and Read, 2007;TEWG, 2009;Arendt et al, 2012b).…”

“…After a variable amount of time in the epipelagic zone, many of these turtles return as juveniles and sub-adults (large juveniles) to nearshore waters and inhabit the neritic zone (Bjorndal et al, 2003), while others alternate between oceanic and neritic foraging grounds (Bolten, 2003a;McClellan and Read, 2007;Mansfi eld et al, 2009). Such habitat shifts refl ect dietary shifts.…”

“…Although some species, such as the loggerhead, Caretta caretta, and green, Chelonia mydas, turtles may vary among populations and individuals in the details of their life history patterns (Hatase et al, 2006;McClellan and Read, 2007;Mansfi eld et al, 2009), all sea turtles begin life as terrestrial hatchlings. Hatchlings crawl to the sea, immediately transitioning to life in the marine environment as they swim offshore (Carr and Ogren, 1960).…”

“…Such habitat shifts refl ect dietary shifts. However, the direction of the cause-effect relationship remains a point of discussion (Witzell, 2002;McClellan and Read, 2007;Casale et al, 2008).…”

“…Ontogenetic habitat shifts are particularly common in marine organisms and are widespread among a variety of vertebrates (Price and Grant, 1984;Fishelson et al, 1987;Lind and Welsh, 1994;Kitowski, 2003;Page et al, 2005). Marine turtles undergo multiple ontogenetic habitat shifts (Bolten, 2003b;McClellan and Read, 2007;Snover, 2008) as they migrate across ocean basins and along coastal zones (Dodd and Byles, 2003;Eckert et al, 2006;Foley et al, 2008;Girard et al, 2009). Various pelagic or benthic communities serve as temporary homes at different stages and within a single stage of their life cycle (Witzell, 2002;Bolten, 2003a;Polovina et al, 2006;Casale et al, 2008;Witherington et al, 2012).…”