Sea turtles are miraculous. First, they've been around since the late Jurassic, roughly 150 million years ago. Cohorts of the dinosaurs, sea turtles have survived through the challenges of eons, existing still today, where many others have ended their evolutionary run. Second, throughout the centuries and up till today, every living adult sea turtle has overcome the odds, existing as a consequence of chance, skill, and capability. The gauntlet each sea turtle faces in the course of its lifetime goes thus: First, deposited as a clutch of leathery, ping-pong ball-sized eggs into a nesting pit dug by its mother high on the beach, of the 50 to 200 eggs laid, roughly 20 percent will never hatch. Roughly a month and a half after having been laid, the surviving eggs hatch, and the young turtles, each small enough to fit in the palm of your hand, squirm to the surface, emerging from the sand en masse, and making their desperate dash for the sea. Along the way, debris, pitfalls, crabs, gulls, raccoons, and other threats will claim roughly 50 percent of those who rose from the sand. For those that actually reach the surf, they trade one set of threats for another, as they first face the repelling force of the waves, and then find a whole new host of predators awaiting them: Various fish, dolphins, sharks, and sea birds, as the young turtles come to the surface for air. For their first few days of life, should they count themselves amongst the living, the vulnerable turtles swim frantically forward. Ultimately, they will often look to settle in a patch of flotsam, preferably a patch of floating seaweed. Now for the next several months, they will seek to avoid those that would eat them, find that which they might eat themselves, and not fall to the pressures of challenging weather or unfortunate currents. In this phase, roughly 50 percent of those who reach the surf will perish. Ultimately, with the passage of years, the survivors will increase in size, from that of a dinner plate at year one to that of a dinner table, in the case of one species at least, the leatherback, a decade or so later. With size comes some measure of protection. The only truly worrisome predators now are some of the larger shark species-- bulls, tigers, and whites -- and the occasional killer whale. At approximately two decades of age, the survivors will be old enough themselves to breed, and continue the cycle which their very existence heralds. Of those that began as eggs on a distant beach, now less than 10 percent remain, at least, those were the odds prior to significant human interference. Over the past century, and in particular in the last several decades, human endeavors, from beach development to plastic refuse to poaching, long lines, nets, and even noxious chemicals, including oil, have upped the ante for sea turtles, causing their survival rate to drop to around one percent or less, from each nesting cycle. It is this added human pressure which has pushed each of the eight sea turtle species into either a threatened or endangered state. For while they have evolved to overcome a host of obstacles, the most recent has arisen so quickly and at such scale that the species find themselves overwhelmed. So let's quickly recap this cycle of odds. Using a hypothetical nesting season, for females may nest multiple times in a single year, of 1,000 eggs, for sake of ease. 1000 eggs laid. 800 hatch. 400 make it to the water. 200 progress toward adulthood. 20 survive to breeding age -- that is, without human interference. Two survive to breeding age with human interference. So a breeding adult sea turtle is the very embodiment of a long shot. It is the exception, not the rule. A jackpot. It is, in a very real sense, a miracle.
海龟是奇迹般的动物 第一,它们自侏罗纪末就出现在这个世界 大约 1 亿 5000 万年前 身为恐龙的同伴,海龟幸存下来, 并存活了长达亿年 存活至今日,反观它的同伴却结束了演化的旅程 第二,在过去几个世纪直到今天 每只成功存活的成年海龟都克服了难关 它们的存活总归机运、技能、及能力 每只海龟在它一生中面临的挑战有: 首先,海龟妈妈于海滩高处挖出的窝里 产下一窝革质、乒乓球大小的蛋 一窝 50-200 蛋中 大约 20%不会孵化 產卵後過了一個半月 还存活的蛋孵化 成为小海龟,每只比你的手掌要来得小 一群新生命爬上地表 然后开始猛烈地冲向海洋 一路走来,碎片、 坑洞、 螃蟹、 海鸥、 浣熊和其他威胁 会夺走大约50% 从沙里爬出的小海龟的生命 对于那些成功抵达浪潮的 它们将面临新的威胁 它们第一次面对海浪的冲击 然后发现新的猎食者正等待着他们 各种鱼类、 海豚、 鲨鱼 还有当他们浮出水面呼吸所遇上的海鸟 它们生命的前几天 若它们侥幸活存 脆弱的海龟会疯狂地向前游 最后,它们往往会在一团漂浮物下定居 最好是在浮在水面的海草 接下来几个月,它们会设法避开天敌 寻找猎物 并不被恶劣的天气或海洋的乱流所击倒 在此阶段,大约50% 进入海洋的海龟会死亡 最后,经过了几年 存活下来的海龟将会慢慢长大 体型从第一年的盘子大小,变成餐桌大小 举棱皮龟为例,过程可能需要十年以上 体型变大会带来一些保护的功用 现在唯一令它担忧的掠食者是一些较大的鲨鱼: 牛鲨、 虎鲨、大白鲨 和偶尔碰到的杀人鲸 到了约二十岁时 存活下来的海龟将成熟到有繁殖能力 繁衍下一代,见证生命周期的循环 在那些沙滩上的龟卵之中 能活到繁殖年龄的不到一成 至少那是于人类破坏之前的机率 在过去这世纪,特别是在过去的几十年里 人类的活动,如开发海滩 塑胶垃圾、盗猎、延绳钓、网捕、 甚至有毒化学品(包括石油) 让海龟存活下来的困难性增加 导致每一代新生海龟的存活率下降到 百分之一左右或更少 人类所施加的生存压力让世界上的八种海龟 都处于受威胁甚至濒临绝种的状态 虽然演化天择使它们能够克服种种障碍 但最近的障碍急速增加 速度如此之快让海龟无法应变 现在,让我们快速回顾海龟在一生中存活的机率 我们利用一个产卵季节来计算 因为母龟可以在一年中多次产卵 为了方便假设它一次产下 1,000 颗卵 1,000 颗卵之中 800 颗会孵化 400 只成功进入海洋 200 只逐步长大至成年 20 只活到繁殖年龄──这是没有人为干预的结果 在人为干扰下,只有两只会活到繁殖年龄 所以成年海龟是一系列 不可能事件的化身 它是个例外,不是常态 就像头奖一样,它真的是一个奇迹