Greenpeace - Making Waves: How many whales once roamed the sea?

In the late 1700s, when Captain James Cook sailed into Sydney harbour, he claimed "there were whale spouts as far as the eye could see." Callum Roberts, in his book "The Unnatural History of the Sea" gathers similar tales of teeming cetaceans from the accounts of explorers ranging from the 11th to the 16th century. Surely, one thinks, these were the exaggerations of seamen suffering from long-voyage boredom and the possibly hallucinatory effects of rancid food supplies -- or maybe a little too much yo-ho-ho.

Well, unless somebody's been spiking the drinks of geneticists who have contributed to a decade-long study called the "Census of Marine Life," it's time to reassess those tales -- they may have been true.

The History of Marine Animal Populations (HMAP) project, part of the Census of Marine Life, has so far collected records on 70,000 whale encounters that build up a picture of past super-abundance, says Andy Rosenberg of the University of New Hampshire. Meanwhile, the genetic variation found in a handful of whale populations so far analyzed suggests that those that remain came from much larger populations than previous supposed. The analysis is based on the fact that, with succeeding generations, DNA is altered through subtle mutations: The larger the original population, the greater the genetic “drift” evident in the current population.

Why does this matter? It matters because whalers have argued for decades that some whale populations have returned to their original, pre-industrial whaling numbers, and so can be safely hunted. But nobody actually knows what those original numbers were, and what guesses we have made in the past have been based on notoriously unreliable reported kills and backwards extrapolations of current population numbers. The International Whaling Commission's own estimates of the pre-industrial populations of humpback whales were revised when there were shown in the past to be off by as much as a factor of 12. The new study suggests that *those* numbers may be similarly, dare I say "wildly," inaccurate.

There are plenty of reasons a return to commercial whaling is a very bad idea. Our profound ignorance about how many whales once roamed the sea is one of them.

For more on the census, check out this excellent article by New Scientist author Fred Pearce.

It's one more reason why we need to create marine reserves protecting 40% of the world's oceans.