Sea lions have a layer of blubber that helps to insulate them and keep them warm [a sea lion's core body temperature is approximately 7.5°C (99.5°F)]. Their blubber is also used as an excess energy reserve (mostly fats and proteins) to metabolize later. This is specifically important for male sea lions, since they do not eat during the breeding season. If you ever see a sea lion laying on the beach, it is not necessarily a bad thing. Sea lions often regulate their body temperature by either laying on the warm sand to rest or, if they are in the open sea, lifting one or more flippers out of the water. The warmth from the sun will cause their blood vessels to vasodilate, or expand, which allows them to release or absorb heat to the environment. Sea lions keep themselves cool by spending long periods of time in the water, laying on wet sand, or resting in a shady area.

Sea lions are incredibly agile and move very well in the water. It is estimated that sea lions can reach up to approximately 13 mph, though they typically cruise at slower speeds. Most of their diet can be found in more shallow waters, so it is not necessary for them to dive incredibly deep on a routine basis. They are capable, however, of diving to almost 274m (900ft)! California sea lions are able to conserve oxygen as they have a higher blood volume than other non-diving mammals of the same size. This increased volume allows for more oxygen-binding in the blood and, like dolphins, California sea lions are able to pull blood away from their extremities and towards their heart and their brain. California sea lions while diving are also able to slow their heart rate from approximately 95 beats per minute (bpm) to about 25 bpm [3].

Although they cannot echolocate like dolphins, sea lions have excellent low light vision and underwater directional hearing.

Sleep

Sea lions commonly sleep on land on rocky outcroppings, but they can also sleep in the water. They have been found to sleep and rest in a variety of positions, including upright with their heads back and their noses pointed upwards toward the sky. Scientists have shown that some species in the sea lion family, known as the otariids, have unihemispheric sleep, similar to cetaceans, including the northern fur seal, Cape fur seal, Steller's sea lion, and southern sea lion [8].