The survival of the sea turtle

2,039,123 views ・ 2012-07-23

TED-Ed


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Sea turtles are miraculous.
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First, they've been around since the late Jurassic,
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roughly 150 million years ago.
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Cohorts of the dinosaurs,
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sea turtles have survived through the challenges of eons,
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existing still today,
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where many others have ended their evolutionary run.
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Second, throughout the centuries and up till today,
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every living adult sea turtle has overcome the odds,
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existing as a consequence of chance,
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skill, and capability.
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The gauntlet each sea turtle faces in the course of its lifetime goes thus:
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First, deposited as a clutch of leathery, ping-pong ball-sized eggs
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into a nesting pit dug by its mother high on the beach,
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of the 50 to 200 eggs laid,
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roughly 20 percent will never hatch.
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Roughly a month and a half after having been laid,
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the surviving eggs hatch,
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and the young turtles, each small enough to fit in the palm of your hand,
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squirm to the surface, emerging from the sand en masse,
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and making their desperate dash for the sea.
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Along the way, debris, pitfalls, crabs,
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gulls, raccoons, and other threats
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will claim roughly 50 percent of those who rose from the sand.
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For those that actually reach the surf,
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they trade one set of threats for another,
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as they first face the repelling force of the waves,
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and then find a whole new host of predators awaiting them:
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Various fish, dolphins, sharks, and sea birds,
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as the young turtles come to the surface for air.
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For their first few days of life,
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should they count themselves amongst the living,
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the vulnerable turtles swim frantically forward.
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Ultimately, they will often look to settle in a patch of flotsam,
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preferably a patch of floating seaweed.
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Now for the next several months,
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they will seek to avoid those that would eat them,
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find that which they might eat themselves,
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and not fall to the pressures of challenging weather
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or unfortunate currents.
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In this phase, roughly 50 percent of those who reach the surf
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will perish.
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Ultimately, with the passage of years,
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the survivors will increase in size,
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from that of a dinner plate at year one
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to that of a dinner table,
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in the case of one species at least, the leatherback,
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a decade or so later.
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With size comes some measure of protection.
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The only truly worrisome predators now are some of the larger shark species--
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bulls, tigers, and whites --
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and the occasional killer whale.
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At approximately two decades of age,
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the survivors will be old enough themselves to breed,
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and continue the cycle which their very existence heralds.
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Of those that began as eggs on a distant beach,
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now less than 10 percent remain,
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at least, those were the odds prior to significant human interference.
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Over the past century, and in particular in the last several decades,
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human endeavors, from beach development
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to plastic refuse to poaching, long lines, nets,
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and even noxious chemicals, including oil,
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have upped the ante for sea turtles,
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causing their survival rate to drop to around one percent or less,
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from each nesting cycle.
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It is this added human pressure which has pushed
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each of the eight sea turtle species
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into either a threatened or endangered state.
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For while they have evolved to overcome a host of obstacles,
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the most recent has arisen so quickly
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and at such scale that the species find themselves overwhelmed.
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So let's quickly recap this cycle of odds.
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Using a hypothetical nesting season,
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for females may nest multiple times in a single year,
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of 1,000 eggs, for sake of ease.
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1000 eggs laid.
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800 hatch.
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400 make it to the water.
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200 progress toward adulthood.
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20 survive to breeding age --
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that is, without human interference.
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Two survive to breeding age with human interference.
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So a breeding adult sea turtle is the very embodiment of a long shot.
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It is the exception, not the rule.
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A jackpot.
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It is, in a very real sense,
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a miracle.
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