Why Do Some Whales Have Weight Limits?

Matthew Savoca, Jeremy Goldbogen

Environment, Americas

Whales are big but could they be bigger?

Both toothed and baleen (filter-feeding) whales are among the largest animals ever to exist. Blue whales, which measure up to 100 feet (30 meters) long and can weigh over 150 tons, are the largest animals in the history of life on Earth.

Although whales have existed on this planet for some 50 million years, they only evolved to be truly gigantic in the past five million years or so. Researchers have little idea what limits their enormous size. What is the pace of life at this scale, and what are the consequences of being so big?

As scientists who study ecology, physiology and evolution, we are interested in this question because we want to know the limits to life on Earth, and what allows these animals to live at such extremes. In a newly published study, we show that whale size is limited by the largest whales’ very efficient feeding strategies, which enable them to take in a lot of calories compared to the energy they burn while foraging.

Ways to be a whale

The first whales on Earth had four limbs, looked something like large dogs and lived at least part of their lives on land. It took about 10 million years for their descendants to evolve a completely aquatic lifestyle, and roughly 35 million years longer for whales to become the giants of the sea.

Once whales became completely aquatic some 40 million years ago, the types that succeeded in the ocean were either baleen whales, which fed by straining seaweater through baleen filters in their mouths, or toothed whales that hunted their prey using echolocation.