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. In particular, accelerometers in the tags could record the sudden changes of speed,
such as lunging movements, that are associated with predatory behaviours.
Counting whale hunts per dive in this way, and knowing from previous studies what types of prey particular cetaceans favour,
the researchers were able to work out the feeding efficiencies—energy in versus energy out—of the two sorts of whale.
Toothed whales, they found, are living on the edge, size-wise.
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.
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.
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, know to have lived. Might its descendants be larger yet?