Blubber is a thick layer of fat, also called adipose tissue, directly under the skin of all marine mammals. Blubber covers the entire body of animals such as seals, whales, and walruses—except for their fins, flippers, and flukes. Blubber an important part of a marine mammal's anatomy. It stores energy, insulates heat, and increases buoyancy. Storing EnergyEnergy is stored in the thick, oily layer of blubber. The energy stored in blubber includes both proteins (mostly collagen) and fats (mostly lipids). The ability of blubber to use these stored nutrients means marine mammals are not forced to search for food for long periods of time. Nursing mothers, for instance, build up thick stores of blubber before giving birth. In addition to feeding offspring, mothers cannot regularly search for food. They rely on the energy stored in their blubber. InsulationBlubber also insulates marine mammals, or helps keep them warm in icy waters. This insulation is necessary. Mammals are warm-blooded, meaning their body temperature stays about the same no matter what the temperature outside is. Keeping a warm body temperature in cold water requires more energy than keeping a warm body temperature in warm water. Some marine mammals, such as sea otters, have a thick fur coat, as well as blubber, to insulate them. To insulate the marine mammal, blood vessels in blubber constrict, or get smaller, in cold water. Constricted blood vessels reduce the flow of blood, thus reducing the energy required to heat the body. This conserves heat. BuoyancyFinally, blubber helps marine mammals stay buoyant, or float. Blubber is generally less dense than the ocean water surrounding it, so animals naturally float. Animals with the thickest blubber, such as right whales, are found in Arctic and Antarctic regions. In these animals, blubber is more than a foot thick! The thickness of their blubber does not indicate better energy storage, insulation, or buoyancy, however. Those characteristics are determined by the chemical property of the blubber. People and Blubber Many ancient cultures of the Arctic relied on blubber as a staple part of their diet. Muktuk, for example, is a traditional food consumed by the Eskimo and Inuit people, native to the U.S. state of Alaska and the Canadian Arctic. Muktuk is thick slices of whale blubber and skin. Besides being an excellent source of energy and vitamin D, muktuk was often the chief source of vitamin C for these Arctic people. (Citrus trees, whose fruit is probably the most familiar source of vitamin C, do not grow in such cold temperatures.) Today, the process of biomagnification has made consumption of muktuk and other whale meat a possible health risk. Biomagnification is the process in which the concentration of a substance increases as it passes up the food chain. Blubber's high concentration of toxic substances may be a result of marine mammals' position as top predators in the marine food web. High concentrations of PCBs, chemicals that can cause cancer, and other toxins have been detected in blubber. The concentrations may be natural, or it may be augmented by bioaccumulation of marine pollution. Some countries, such as Japan and Norway, continue to harvest whale blubber for food. Environmental groups have expressed concern about the high concentration of PCBs in the blubber. WhalingBlubber was the basis of the whaling industry, one of the most lucrative businesses of the 18th and 19th centuries. Millions of whales were hunted throughout the Atlantic, Pacific, and Arctic oceans in sophisticated whaling "factory ships." After killing a whale and stripping it of its blubber, workers rendered the blubber in enormous iron cauldrons called trypots. Rendering is the process of slowly cooking blubber or other animal fat (such as lard) over a low temperature. As blubber renders, it turns into a waxy substance called whale oil. Whale oil was a primary ingredient in soap, margarine, and oil-burning lamps. Today, some indigenous Arctic communities, such as the Inuit, still harvest blubber and render it for use in traditional whale-oil lamps. The whaling industry dwindled as petroleum and natural gas replaced whale oil as a major fuel source. Vegetable oils replaced whale oil in margarine and soaps. Environmental laws and hunting limits have slowly allowed whale populations to recover.