As present, but at much higher population levels. In the Southern Hemisphere some 150,000 to 200,000 Blue Whales migrated each year to Antarctic waters at the turn of the century. Its size made it a valuable and preferred catch for Whalers resulting in severe depletion of these southern stocks. Harvests of Blue Whales peaked during the 1930 to 1931 season when nearly 30,000 were killed worldwide. Entrapment by ice may be a significant source of mortality in the North Atlantic population.
Deliberate catch is thought to be insignificant at present.
The worldwide moratorium on commercial whaling which took effect in 1986 is the most significant protection measure. Some countries with whaling interests are not members of the IWC Individual Blue Whales have been monitored off of the Gulf of St Lawrence and off of the coast of California by photo-identification. A tourist industry is developing around the Californian Blue Whales and may contribute towards their continued protection. The Blue Whale is the largest animal alive today, and possibly the largest ever. It has been estimated that in a single day a Blue Whale may consume between two and four tonnes of Krill.