Inclination

Sea Turtle Navigation: the magnetic map, inclination and ocean gyre migration

Loggerhead hatchlings leave Florida, ride the Gulf Stream and circle the North Atlantic gyre for years. Dipole-model field and simplified Stommel gyre: a teaching model, not IGRF or an ocean forecast.

Run

Life stage

Remembered signature

Click the globe or map to place a probe.

Map layers

Fill

Field model

Dipole approximation only. Isolines are not the IGRF model.

Ocean, turtles, noise

Experiment 1: magnetic displacement (tank test)

As in Lohmann-style coil experiments: expose the animal to the field of another place and see which way it wants to swim. The model heading is evaluated for the signature chosen above.

Field of

Plot: model heading for the chosen field versus an offset applied to the perceived inclination (orange) or intensity (blue); the other offset stays at its slider value.

Experiment 2: secular variation (hypothesis)

The imprinted signature is fixed; the field drifts. Where would that signature sit later? Toy drift rates, shown as a hypothesis for nesting-coast shifts, not a prediction.

Beach at dusk: hatchlings and artificial light

Switch to the Beach view. Hatchlings crawl toward the brightest, lowest horizon; lamps behind the dune pull them the wrong way. Model: heading = brightness-weighted direction + noise.

Numerical checks

Species card (approximate)

Loggerhead sea turtle (Caretta caretta): adult shell about 0.9 to 1.1 m, mass roughly 100 to 150 kg; hatchlings about 4.5 cm and about 20 g. Reaches maturity after roughly 25 to 35 years (estimates vary). Typical nest: about 100 eggs, incubation about 2 months. The west Atlantic population nests mainly on Florida beaches. Swimming speed of juveniles: of order 0.2 to 0.4 m/s. Values are approximate.

The science