For millennia, humans have been striking out into the sea to hunt some of its largest creatures—whales—for their meat, their bones and their blubber. By the 17th century, our whaling fleets were well organized (and well armed), but it wasn’t until the 20th century that the hunt became a harvest, with factory ships. By the late 1930s, more than 50,000 whales were killed every year.

But until now, researchers haven’t had an official number to encompass the whole impact of that harvest: they didn’t trust the information recorded by the International Whaling Commission, which tallies the whale bodies, reports Daniel Cressey for Nature News. But by relying in part on a painstaking account of illegal whaling, a group of researchers has made the first global estimate of the toll of whaling in the past century. From between 1900 and 1999, they report, approximately 2.9 million whales were killed.

“The total number of whales we killed is a really important number. It does make a difference to what we do now: it tells us the number of whales the oceans might be able to support,” Stephen Palumbi, a marine ecologist at Stanford University in California told Nature News.

In 1986, the International Whaling Commission banned nearly all types of whaling. As a result, populations are rebounding, though they're still not as high as they were before the factory ships started work. Today, only small hunts by indigenous communities and harvests of whales that fall under the what's called the "research exemption" are allowed. (But the latter are still controversial: the United Nations’ International Court of Justice have questioned whether, for example, Japan’s whaling practices really reflect the numbers needed for research.)

Still, the 2.9 million figure is a lower bound for the estimate. To put the number in perspective, Cressey reports that other massive hunts probably resulted in more animal deaths, but that the size whales makes the 20th century harvest "the largest cull of any animal — in terms of total biomass — in human history."