Meeting Abstract

64.2  Thursday, Jan. 6  Loggerhead Sea Turtle Migrations and Secular Variation: Navigating Through an Ever-changing Geomagnetic Environment PUTMAN, NF*; LOHMANN, KJ; UNC Chapel Hill; UNC Chapel Hill nputman@email.unc.edu

Hatchling loggerhead sea turtles (Caretta caretta) from eastern Florida migrate offshore to the North Atlantic subtropical gyre, a circular current system that flows around the Sargasso Sea. During the next several years, young turtles follow a circular migratory pathway around the Atlantic before eventually returning to the North American coast. Experiments have demonstrated that young loggerheads respond to regional magnetic fields that exist along the pathway by swimming in directions that would, in each case, help them advance along the migratory route. The responses appear to be inherited, yet a fascinating aspect of the system is that the Earth’s magnetic field gradually changes. This change in the field, known as secular variation, presumably imposes a degree of imprecision on the open-ocean navigation of young turtles. As a first step toward exploring these issues, we analyzed results from magnetic orientation experiments with hatchling loggerheads in the context of geomagnetic and oceanic constraints. The results indicate that magnetic fields capable of eliciting strong directional responses from turtles typically exist at geographic locations that fulfill several criteria: (i) they are along the main migratory pathway of the turtles and are thus probably encountered by numerous individuals; (ii) they have water temperatures favorable for growth and survival; and (iii) they are areas where the Earth’s field has been relatively stable for the past century (i.e., rates of secular variation have been low). Our findings suggest that secular variation might have important but previously unrecognized ecological consequences, ranging from influencing the spatial distribution of pelagic-stage turtles to shaping temporal nesting trends of adults.