The Limits of Ocean's Heavyweights: Diet Plays Big Role in How Huge Whales Can Get

Have you ever wondered why whales are big but aren't bigger? Science now has an explanation for it.

A new study says that the whale's body size is influenced by how whales capture their prey and how much food is available, researchers reported Thursday in the journal Science.

The study involved 90 blue whales, the most massive animals to ever live. While size varies, the American Cetacean Society explains that blue whales could grow about 100 feet (30 meters) long and weighs more than 100 tons (91,000 kilograms). The study also included the sperm whale - the world's biggest whale with teeth - that could stretch about 60 feet (18 meters) long, the group added.

Sperm whales capture one prey at a time when they hunt, attempting them out in the dark depths with a sonar-like exposure. The researchers noted that whales become progressively less efficient in hunting and obtain fewer calories from their meals per calorie burned in each dive as their body size increases.

Big gulps

The study says the blue whale could be bigger since it feeds in an extraordinarily different and highly effective way. Blue whales open their mouth widely and engulf an enormous volume of water that is bigger than its body size as it swims along.

Lunge-feeding whales, which engulf swarms of krill or forage fish with massive gulps, get the most bang for their buck. The whales use more energy in lunging as they increase in size - but their gulp size increases even more dramatically.

In other words, the bigger the whale becomes, the bigger the gulp becomes, resulting in higher energy efficiency. Whales' size is set by the density, extent, and seasonal persistence of their prey.

Jeremy Goldbogen of Stanford University, one of the study's authors, said the whales use a vast resource that's very rich in a small amount of time.

The researchers added the total amount of energy that it gained from foraging, relative to the energy, expands in finding and consuming prey.

Why aren't they even bigger than they are?

Goldbogen presumed that blue whales are limited by the seasonal nature of the "most nutritious" krill patches, which grow gigantic and dense in the summer. Calculations, according to Golbogen, show that the density of prey is just not seen anywhere in the world to sustain a blue whale that's 115 feet (35 meters) long.

Goldbogen added there are limiting factors in how their bodies function. He noted a recent study that found a blue whale's heart beats up to 37 times a second after deep dives, which is as fast as the organ could pump.

Terrie Williams of the University of California, Santa Cruz, who did not participate in the research, said another limiting factor could be a whale's capacity to process the food it takes in.

She said the research provided a complete look across large whale species, and the completion in collecting the data "boggles the mind."

"You try to go out and put a [small] tag on the back of the [largest] animal in the world," she said.