如果这个世界没有鲨鱼

It's safe to say that most folks would be comfortable imagining a world without sharks. Whether you're a surfer who spends as much time scanning the waters for predators as looking for the next big rip curl or an ordinary beachgoer who's experienced the terror of sprinting to shore when a lifeguard goes heavy on the whistle, most of us would take to the seas with a little more ease knowing there aren't any hammerheads, blacktips or bull sharks patrolling the waters below. The truth is, however, that we need them more than we think.

可以说，一个没有鲨鱼的世界会让大多数人感到舒服。无论你是一个花费大量时间在海上娱乐的冲浪爱好者还是一位严阵以待的救生员，当你知道水面下没有任何锤头鲨、黑鳍鲨或者牛鲨时，你可能会更加安心一点。但事实上，我们比我们想象的更需要鲨鱼。

Sharks killed 10 people in 2013. Humans, on the other hand, cull the shark population by somewhere from 30 million to 70 million each year. The steady decline in sharks appears to be having a devastating effect on the aquatic ecosystem that could wind all the way up to your dinner plate. That's because a lack of sharks throws off the food chain that's been a way of life under the sea for hundreds of millions of years.

2013年，在全世界范围内，鲨鱼杀死了10人。但与此同时，人类每年杀戮的鲨鱼数量从3000万增加到了7000万。鲨鱼数量的稳步下降会对水域生态系统造成毁灭性的影响，这种影响可能还会波及到你的晚餐。这一切都是因为鲨鱼的缺席使得食物链失去了原本的作用，而这些食物链已经在海底存在了几亿年了。

Sharks are apex predators. That means the big ones are at the top of the seafood chain. They dine on smaller fish — like tuna — which in turn eat even smaller, bottom-feeding species — like scallops — that survive largely on algae. Without sharks to keep down the population, those algae-eaters are more likely to be swallowed up by their natural predators, who rise to the top of the chain with no one to hunt them. Absent the bottom-feeders, algae grow wild, damaging coral reefs and other vegetation, as well as clogging up fish gills and contaminating seafood and water .

鲨鱼几乎可以说是顶级的捕食者了，它们处在海洋食物链的顶端，它们以稍小一点的鱼类为食，比如金枪鱼。而金枪鱼又反过来吃那些更小的海洋生物，比如扇贝。扇贝几乎算是食物链的底层了，它们主要靠海藻生存。如果没有鲨鱼来控制金枪鱼的种群数量，这些金枪鱼就会爬到食物链的顶端，那些底层食藻动物的数量就会因为被大量捕食而减少。这样一来，藻类就会疯长，从而破坏珊瑚礁和其他植被。与此同时，这些失控的藻类也会堵塞鱼鳃、污染海水。

An ocean free of sharks would also change the way that other marine life moves around. Shark prey would no longer be forced into remote areas less conducive to living and reproducing. That's because they wouldn't have to constantly be looking over their shoulders to see if they're on the lunch menu .

如果海洋里没有了鲨鱼，其它海洋生物的栖息地也会被改变。鲨鱼的猎物们将不再被迫进入不利于生存和繁殖的偏远地区，因为它们不再需要整天提心吊胆。

If that's not enough to convince you that sharks need to be here to stay, think about your own belly. Without sharks to help control the population underwater, midsize fish will be free to fatten themselves up on sea life that might otherwise make it to your plate. That's exactly what happened off the coast of North Carolina, where excess fishing of sharks decimated what were once thriving scallop, oyster and clam populations.

如果这些还不足以让你相信我们确实需要鲨鱼，想想你自己的晚餐。如果没有鲨鱼来帮助控制海洋里的人口，像金枪鱼这样的中型鱼会在海洋中自由地增肥，最终它们会进入你的盘子。这正是北卡罗来纳州沿海地区发生的事情，在那里，过度捕捞鲨鱼使曾经繁荣的扇贝、牡蛎和蛤蜊种群大量死亡。