The blue whale is the largest animal known to have lived – larger than any dinosaur or currently living animal. It can grow up to 33 m long (27 m long in the northeast Pacific) and weigh up to 150,000 kg. Despite its large size, the blue whale feeds almost exclusively on krill. Blue whales in the northeast Pacific are thought to spend their summers feeding off the coast of the U.S. and Canada, and their winters in the tropical and subtropical waters off of Mexico and Central America. The presence of mother and calf pairs off the Gulf of California from December to March suggests that blue whales may breed and calve in the winter, though no breeding ground has been identified and their mating habits are not known. Their lifespan is also not known.