The diet of the largest animal ever known, the blue whale, is mainly composed of one of the smallest: krill.

Blue whales, weighing around 200 tons, feed exclusively on krill and require massive amounts to sustain their large size. Having been hunted to near extinction by historical whaling, blue whales now need krill to fuel their reproduction to recover their populations.

Krill hotspots such as the Chiloé-Corcovado region in southern Chile have historically been recognized as blue whale feeding sites. Southern Hemisphere blue whale populations nurse their calves in Chiloé-Corcovado to take advantage of the abundant krill supply. Similarly, off the West Coast of the United States, during summer months blue whales concentrate in prime feeding areas including the Channel Islands, Monterey Bay and Cordell Bank north of San Francisco, California, to feed on dense swarms of krill.

Krill fisheries, operating in the Southern Ocean and around Japan, harvest krill for human consumption and aquaculture feed. Increasing demand for new products, such as krill oil, may further reduce krill populations and stress blue whale survival.