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AnimalsTranscript
00:00 (upbeat music)
00:02 Sea turtles are ancient mariners.
00:05 Present in all but Earth's coldest oceans,
00:08 these marine reptiles are well adapted
00:11 to a life on the moons.
00:13 Sea turtles have existed since the time of the dinosaurs.
00:21 The earliest known marine turtle
00:23 lived about 120 million years ago.
00:26 Named Desmotochilus patelli,
00:28 it was six feet long and had the characteristic features
00:31 of modern sea turtles,
00:33 including a carapace or top shell and paddle-like limbs.
00:38 Today, there are seven species of sea turtles,
00:41 with the largest being the leatherback.
00:43 Growing as long as eight feet
00:44 and weighing up to 2,000 pounds,
00:47 it is larger than known fossils
00:49 of its prehistoric ancestor, D. patelli.
00:52 Sea turtles can lay more than 150 eggs at a time.
00:58 Called a clutch, these large egg deposits
01:01 help ensure the survival of sea turtle hatchlings.
01:04 Once a female lays her eggs, she returns to the sea,
01:08 leaving her hatchlings to fend for themselves.
01:11 Fewer than 0.1% of hatchlings survive to adulthood,
01:18 in part due to numerous predators on the beach.
01:21 Emerging in large numbers increases the chance
01:23 that some will survive.
01:25 (water splashing)
01:29 A sea turtle's sex is determined by temperature.
01:32 Unlike most vertebrates, a sea turtle's sex
01:36 is not determined by sex chromosomes.
01:38 Instead, the temperature of the nest
01:40 determines the sex of the hatchlings.
01:43 When temperatures are warm, at about 88 degrees Fahrenheit,
01:47 most of the hatchlings will be female.
01:49 But when temperatures are cooler,
01:51 less than around 82 degrees Fahrenheit,
01:54 most of the hatchlings will be male.
01:56 Sea turtles use Earth's magnetic fields to navigate.
02:01 Sea turtles have geomagnetic abilities,
02:04 which serve as an internal GPS.
02:07 The turtles have particles of magnetite,
02:10 a magnetic mineral, in their brains.
02:12 The magnetite likely plays a role
02:14 in orienting sea turtles to Earth's magnetic poles,
02:17 similar to a compass.
02:20 Baby sea turtles imprint on the unique magnetic signature
02:23 of the beaches where they hatch.
02:26 This magnetic map can guide them back to the same beaches
02:29 several years later to lay their own eggs.
02:32 All seven sea turtle species are threatened with extinction.
02:40 Once abundant, sea turtle populations
02:43 have dramatically declined in the past two centuries.
02:46 Fishing is a major threat to sea turtles,
02:50 as they become caught in fishing nets as bycatch,
02:53 or accidental catch.
02:55 Illegal harvesting of turtle eggs,
02:57 trafficking in turtle products,
02:59 and ocean pollution are also concerns.
03:02 However, policies have been enacted to reduce bycatch,
03:06 protect turtle habitats,
03:08 and prohibit the killing of sea turtles and their eggs.
03:11 By continuing this kind of intervention,
03:14 humans can help stop the decline of sea turtles,
03:17 helping keep these ancient mariners in the world's oceans.
03:21 (waves crashing)
03:23 (upbeat music)
03:26 (upbeat music)
03:29 (upbeat music)
03:32 (upbeat music)
03:36 (upbeat music)
03:38 (upbeat music)
03:41 (upbeat music)
03:43 you