Baleen whales feed by opening their gigantic maws, lunging forward in the water and engulfing gallons of seawater in their mouths. They strain the seawater back through their baleen plates, trapping vast numbers of tiny critters—fish, krill and others—that then get swallowed all at once. The species that share this method include what are called the rorqual whales, which include fin whales, sei whales, blue whales and humpback whales.

　　须鲸是这样进食的。它们敞开胃口，在水里面向前猛扑，然后使嘴里里面吞下大量的海水，通过长须盘过滤，将海水挤出，网货大量的小生物，例如鱼、磷虾以及其他小生物，接着瞬间将它们囫囵吞下。利用这种方法进食的鲸类包括所说的鰛鲸，这类鲸有塞鲸、蓝鲸以及座头鲸等。

　　But now a team of Japanese and Thai researchers has discovered a never-before-seen type of feeding behavior in a rorqual called a Bryde’s whale. These whales don’t bother with the lunge. They simply open their mouths at the surface and let the seawater flow in, before straining and expelling the seawater through their baleen as usual.

　　现在却有一日本研究组和泰国研究人员发现一种称作南非鲸的鰛鲸，这类鲸的进食方式之前从未见过。这些鲸进食不动用肺。如通常情况一样，在通过须盘将海水从口中挤压出去之前，它们只是简单地在水面上张开口让海水涌入。

　　The researchers call it tread-water feeding because of the way the whales gently undulate their tails to keep their heads near the surface of the water. They say it’s the first passive feeding strategy ever seen in a baleen whale. The team, led by Takashi Iwata from the University of Tokyo, observed 31 different whales feed this way in the Gulf of Thailand.

　　由于这些鲸轻轻地挥动它们的尾巴，让头部靠近水面，因此这些研究人员称这种进食方式为踩水进食。他们称这种被动进食策略在须鲸中是首次被发现的。东京大学盐田龙志领导的研究小组在泰国湾观察到了31种不同的鲸鱼用这种方式进食。

　　Tread-water feeding is more energy-efficient than lunge-feeding, since the whales just have to bob their heads near the surface. But Iwata thinks that the odd behavior may have a darker origin.

　　由于这些鲸必须摆动头部才能靠近水面，所以这种踩水进食方式比用肺进食更加有效。但岩田认为，这种奇怪的进食方式可能来路不明。

　　The upper Gulf of Thailand is hypoxic—there’s a serious lack of oxygen dissolved in the water, thanks mostly to sewage that flows into the sea from nearby rivers. The low oxygen levels might force the whales’ prey towards the surface, where oxygen is a bit more plentiful. And if all the food is in one spot, then tread-water feeding might be the only way to get enough nutrition. Which means that these whales apparently improvised an improved strategy for survival in their polluted habitat.

　　上述的泰国弯海水含氧量低，即溶解在水里面的氧含量严重缺少，造成这种现象的原因，大部分情况是附近河流被注入的污水流入大海。含氧量水平低迫使这些鲸鱼趋向水面含氧量丰富的地方猎食。如果所有的猎物都聚集在一个地方，那么这种踩水进食可能是唯一一种获得充足营养的进食方式。也就是说，很明显为了能够在受污染的栖息地生存下来，它们临时采取了这种改良的进食策略。

　　Iwata wrote in an email that his team witnessed tread-water feeding most often in adult-calf pairs. That observation leads him to suspect that the behavior might be socially learned, passed from parents to their offspring via imitation.

　　岩田在一封邮件中写到，他的团队经常目睹这些成年鲸鱼成双成对地以踩水方式进食。观察到这种想象后，他心生疑惑，这种行为可能是社会群体知识，通过模仿他们的后代从父母那里学习过来。

　　If that’s true, then tread-water feeding could represent a form of culture, unique to the Bryde’s whales that live in the Gulf of Thailand.

　　如果这种怀疑是真的，那么这种踩水进食的方式可能代表着一种文化的形成，而它只存在于栖息在泰国湾的南非鲸鱼中。