Complex sentence: Loggerhead and green turtles can detect the orbital movement of waves and use this information to swim perpendicular to the waves meaning they swim offshore since close to the shore, wave crests are parallel to the beach.
Split into simpler sentences: Loggerhead and green turtles can detect the orbital movement of waves and use this information to swim perpendicular to the waves crests. This means they swim offshore, since close to the shore, wave crests run parallel to the beach.