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Why are whales so big? One answer is simply that they can be. The size of land animals is constrained in part by their need to support themselves against the force of gravity. Marine creatures have that support provided free, by the medium they live in.
為什麼鯨魚的體型如此龐大？有一個答案很簡單，它們就是能長到這麼大。陸地動物體型受限的部分原因是因為它們需要依靠自身對抗地心引力。海洋生物可以通過它們生活的環境為媒介免費獲得這種支持。
Even so, what is possible is not always sensible. Resources put into growth are unavailable for reproduction. Given that whales can and do become big, however, a second question arises: what, if anything, stops them being even bigger? Jeremy Goldbogen of Stanford University and his colleagues suspect that the answers to both questions are related to the animals' food supply.
即便如此，可能的事情並不總是明智的。投入生長的資源無法再生產。鑑於鯨魚可以且確實龐大，第二個問題就來了：如果有的話，有什麼可以阻止它們變得更大？斯坦福大學的Jeremy Goldbogen和他的同事懷疑兩個問題的答案和動物的食物供應有關。
And, as they describe in a paper in Science, they have gathered data that illuminatehow this might work. Broadly, big whales come in two varieties. Toothed whales, such as sperm whales, hunt individual prey.
正如他們在《Science》雜誌中發表的一篇論文所述，他們收集了數據，闡明瞭可能的運作方式。總的來說，大鯨魚有兩種。齒鯨，如抹香鯨，捕食單個獵物。
Baleen whales suck in mouthfuls of water and extract small organisms such as krill, using fibrous buccal filters. The biggest whales of all (blue, humpback and so on) are baleen whales. This might be viewed as paradoxical, because on land, as predators get bigger, so do their individual prey.
鬚鯨，用纖維狀的口腔過濾器吸入大量的水，並從磷蝦等小生物中吸取營養。所有鯨魚中最大的鯨類（藍鯨、座頭鯨等）是須鯨。這或許被認為是很矛盾的，因為在陸地上，捕食者越大，它們的獵物也越大。
Both toothed and baleen whales often hunt by diving deep—prey being more abundant at depth. To do this they have to hold their breath, which limits how long they can stay underwater. One explanation of giantism in whales is that because bigger whales can hold their breath longer, they can spend more time hunting.
齒鯨和鬚鯨通常都潛入深海捕食，因為深海里的獵物更多。為了去深海捕食，它們會屏住呼吸，這就限制了它們在深水中停留的時間。鯨魚巨大體型的解釋之一是因為體型越大，屏息時間越長，這樣它們就能花更長時間在深海捕食。
But that will only hold good as long as the extra time is spent productively. Dr Goldbogen and his team attached water-and-pressure-proof data-recording tags to a range of both toothed and baleen cetaceans, to see what they got up to on their hunting dives.
對於鯨魚巨型化的一種解釋是，體型越大的鯨魚屏住呼吸的時間越長，它們才有更多的時間去捕獵。但只有在額外的時間能有效捕獵的情況下，這一理論才能成立。戈德伯格和他的團隊將防水且耐壓的數據記錄儀分別安置在齒鯨和鬚鯨身上，從而記錄它們在潛水時的行為。
Toothed whales, they found, are living on the edge, size-wise. The number of individualprey they are able to chase and capture in a single dive is just enough to sustain animals of their size.
他們發現，齒鯨就體型而言已經到達了極限。它們每次下潛能夠捕捉到的單個獵物的數量僅夠維持它們現有的體型。
By contrast, the baleen whales the researchers looked at, once they have encountered a shoal of prey, are in nutritional nirvana. 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.
相比之下，研究人員觀察到，鬚鯨一旦遇到了一群獵物，就彷彿進入了充滿營養的天堂。它們估計，一隻大鬚鯨一次潛水所能捕獲食物的量是齒鯨所能捕獲到的最大單個獵物的十倍。
Toothed whales thus do seem to have hit some sort of size limit. Perhaps, though, baleen whales might continue to evolve and get bigger still. The blue whale is, at the moment, the largest animal, extant or extinct, known to have lived. Might its descendants be larger yet?
因此，齒鯨似乎確實到了其體型的極限。不過，鬚鯨或許會繼續進化，從而變得更大。目前，藍鯨是目前已知的（現存的或已滅絕的）體型最大的動物。它的後代會變得更大嗎？
重點單詞：
prey [preɪ] n.n.犧牲者；被掠食者，獵物
illuminate [ɪ'lumɪnet] v.照亮，照明;闡明，說明
paradoxical [,pærə'dɑksɪkl] adj. 矛盾的;反常的,荒謬的;反論的
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