Wave Orientation - Field Experiments

WAVE ORIENTATION - FIELD EXPERIMENTS

Immediately after entering the sea, hatchlings establish a course toward the open ocean and maintain it as they swim away from shore. To determine if turtles rely on the direction of ocean waves to guide themselves seaward, hatchlings were tethered inside a floating orientation arena placed at various distances offshore along the Florida coast .

Results:

Hatchlings tethered in the arena swam into approaching waves whenever waves were present.
Hatchlings tethered in the arena during times when the water was still and no waves were present circled the arena aimlessly or oriented toward apparently random directions.

References: (Salmon & Lohmann 1989, Lohmann et al. 1990)

In a second series of experiments, green turtle hatchlings were released at sea under typical conditions when waves moved shoreward and during unusual weather conditions when waves moved in atypical directions.

Results:

The hatchlings swam into waves in all experiments, even when doing so resulted in orientation back toward land.

Reference: (Lohmann & Lohmann 1992)

Interpretation:

Hatchling sea turtles maintain seaward orientation early in the offshore migration by using wave propagation direction as an orientation cue. Because waves and swells entering shallow, coastal areas are refracted until they approach a beach directly, swimming into waves reliably guides turtles away from land and toward the open sea.

Next Question:
These results raise a new question. To use waves as an orientation cue, hatchlings entering the ocean at night must be able to determine wave direction while swimming under water in almost total darkness. How can they do this?