Humpback whale numbers in the northern Pacific Ocean have ballooned to nearly 20,000, the largest population seen since the majestic mammals were hunted nearly to extinction half a century ago. The number of humpbacks hit an all-time low of1,400 or even lower by 1966, when their hunting was banned internationally. The new census, from one of the largest whale studies ever undertaken, shows that the animals have rebounded much better than expected.