The blue whale - Balaenoptera musculus is a marine mammal belonging to the suborder of baleen whales called Mysticeti and is arguably the most impressive creature to live or have ever lived on this planet! At 30 metres in length and 180 metric tons or more in weight, it is in fact the largest animal ever known to have existed!

Long and slender, the blue whale's body can be various shades of bluish-grey dorsally and somewhat lighter underneath.

There are at least three distinct subspecies: B. m. musculus of the North Atlantic and North Pacific, B. m. intermedia of the Southern Ocean and B. m. brevicauda (also known as the pygmy blue whale) found in the Indian Ocean and South Pacific Ocean. B. m. indica, found in the Indian Ocean, may be another subspecies.

So, just what does a Blue Whale eat?

Blue whales feed almost exclusively on krill, though they also take small numbers of copepods. Copepods - meaning 'oar-feet', are a group of small oceanic crustaceans, but they are also found in nearly every freshwater habitat. The species eaten by blue whales are planktonic (as in drifting in sea waters), although there are some benthic species which live on the ocean floor.

The species of copepod zooplankton eaten by blue whales will vary from ocean to ocean. In the North Atlantic, Meganyctiphanes norvegica, Thysanoessa raschi, Thysanoessa inermis and Thysanoessa longicaudata are the usual food, while in the North Pacific, Euphausia pacifica, Thysanoessa inermis, Thysanoessa longipes, Thysanoessa spinifera, Nyctiphanes simplex and Nematoscelis megalops are taken. Then, in the Antarctic, blue whales eat Euphausia superba, Euphausia crystallorophias and Euphausia valentin.

Blue Whales and Krill

An adult blue whale can eat up to 40 million krill in a day. The whales always feed in the areas with the highest concentration of krill, sometimes eating up to 3,600 kilograms (7,900 lb) of krill in a single day. This daily requirement of an adult blue whale is in the region of 1.5 million kilocalories.

Because krill move through the ocean levels, blue whales typically feed at depths of more than 100 metres (330 ft) during the day and only surface-feed at night. Dive times are typically 10 minutes when feeding, though dives of up to 20 minutes are common. The longest recorded dive is 36 minutes.

The blue whale feeds by lunging forward at groups of krill, taking the animals and a large quantity of water into its mouth. The water is then squeezed out through the baleen plates by pressure from the ventral pouch and tongue. Once the mouth is clear of water, the remaining krill, unable to pass through the plates, are swallowed. The blue whale also incidentally consumes small fish, crustaceans and squid caught up with krill.

The Future for Blue Whales

Blue whales were abundant in nearly all of the earth's oceans until the beginning of the twentieth century. Unfortunately for over a century they were hunted almost to extinction by whalers until they were protected by the international community in 1966.

A 2002 report estimated there were 5,000 to 12,000 blue whales worldwide, located in at least five groups. More recent research into the Pygmy subspecies suggests this may be an underestimate. Before whaling, the largest population was in the Antarctic, numbering approximately 239,000 (range 202,000 to 311,000). There remain only much smaller (around 2,000) concentrations in each of the North-East Pacific, Antarctic, and Indian Ocean groups. There are two more groups in the North Atlantic, and at least two in the Southern Hemisphere.

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