Why are whales so big? One answer is simply that they can be.
为什么鲸鱼的体型如此庞大？有一个答案很简单，它们就是能长到这么大。
The size of land animals is constrained in part by their need to support themselves against the force of gravity.
陆地动物体型受限的部分原因是因为它们需要依靠自身对抗地心引力。
Marine creatures have that support provided free, by the medium they live in.
海洋生物可以通过它们生活的环境为媒介免费获得这种支持。
Even so, what is possible is not always sensible. Resources put into growth are unavailable for reproduction.
即便如此，可能的事情并不总是明智的。投入生长的资源无法再生产。
Given that whales can and do become big, however, a second question arises: what, if anything, stops them being even bigger?
鉴于鲸鱼可以且确实庞大，第二个问题就来了：如果有的话，有什么可以阻止它们变得更大？
Jeremy Goldbogen of Stanford University and his colleagues suspect that the answers to both questions are related to the animals' food supply.
斯坦福大学的Jeremy Goldbogen和他的同事怀疑两个问题的答案和动物的食物供应有关。
And, as they describe in a paper in Science, they have gathered data that illuminate how this might work.
正如他们在《Science》杂志中发表的一篇论文所述，他们收集了数据，阐明了可能的运作方式。
鲸鱼体型之谜(1).jpg
Broadly, big whales come in two varieties. Toothed whales, such as sperm whales, hunt individual prey.
总的来说，大鲸鱼有两种。齿鲸，如抹香鲸，捕食单个猎物。
Baleen whales suck in mouthfuls of water and extract small organisms such as krill, using fibrous buccal filters.
须鲸，用纤维状的口腔过滤器吸入大量的水，并从磷虾等小生物中吸取营养。
The biggest whales of all (blue, humpback and so on) are baleen whales.
所有鲸鱼中最大的鲸类（蓝鲸、座头鲸等）是须鲸。
This might be viewed as paradoxical, because on land, as predators get bigger, so do their individual prey.
这或许被认为是很矛盾的，因为在陆地上，捕食者越大，它们的猎物也越大。
Both toothed and baleen whales often hunt by diving deep—prey being more abundant at depth.
齿鲸和须鲸通常都潜入深海捕食，因为深海里的猎物更多。
To do this they have to hold their breath, which limits how long they can stay underwater.
为了去深海捕食，它们会屏住呼吸，这就限制了它们在深水中停留的时间。
One explanation of giantism in whales is that because bigger whales can hold their breath longer, they can spend more time hunting.
鲸鱼巨大体型的解释之一是因为体型越大，屏息时间越长，这样它们就能花更长时间在深海捕食。
But that will only hold good as long as the extra time is spent productively.
但这只有在额外的时间被有效利用的情况下才有效。
Dr Goldbogen and his team attached water-and-pressure-proof data-recording tags to a range of both toothed and baleen cetaceans,
Goldbogen博士和他的团队将防水和耐压的数据记录标签分别贴在了齿鲸和须鲸的身上
to see what they got up to on their hunting dives. In particular, accelerometers in the tags could record the sudden changes of speed,
以观察它们在潜水时的情况。尤其是标签上的加速器可记录速度的突然变化，
such as lunging movements, that are associated with predatory behaviours.
比如与捕食行为相关的冲刺运动。
Counting whale hunts per dive in this way, and knowing from previous studies what types of prey particular cetaceans favour,
用这种方式记录每次潜水时的鲸鱼捕食活动并根据先前的研究了解某类鲸鱼喜欢的猎物类型
the researchers were able to work out the feeding efficiencies—energy in versus energy out—of the two sorts of whale.
研究人员能够计算出两种鲸鱼的进食效率——输入能量对比输出能量。
Toothed whales, they found, are living on the edge, size-wise.
他们发现就体型而言，齿鲸生活在危险边缘。
The number of individual prey they are able to chase and capture in a single dive is just enough to sustain animals of their size.
它们每次潜入深海中能够捕获的单个猎物数量仅够维持它们这种体型的动物的生存。
By contrast, the baleen whales the researchers looked at, once they have encountered a shoal of prey, are in nutritional nirvana.
相比之下，研究人员观察到的须鲸一旦遇到一群猎物，就处于营养极乐世界。
A single lunge by a large rorqual, they reckon, can capture ten times as much food as the largest individual prey taken by toothed whales.
他们认为一只巨大鳁鲸的一次猛扑所捕获的食物是齿鲸所捕获的最大的单个猎物的十倍。
Toothed whales thus do seem to have hit some sort of size limit.
因此，齿鲸似乎确实有某种体型上的限制。
Perhaps, though, baleen whales might continue to evolve and get bigger still.
不过，也许须鲸会继续进化，变得更大。
The blue whale is, at the moment, the largest animal, extant or extinct, know to have lived. Might its descendants be larger yet?
目前，蓝鲸是已知的现存或已灭绝动物中最大的。它的后代或许会更大？
来源：经济学人
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