There are two important ways that temperature can determine where sharks live and where they migrate. One is sea surface temperature, which is categorized by ocean regions. The other is ocean depth temperature, which is categorized as shallow, deep or open ocean waters.

Sharks can be classified as polar, temperate, or tropical, depending on the surface temperature of the ocean region they inhabit. These temperature regions can be imagined as wide bands drawn over the ocean's surface, showing the range of water temperature within them. The temperature of the water is a major factor determining whether sharks migrate.

Ocean Regions

Heat from the sun warms the world's oceans near the Equator. This heat is gradually circulated through the oceans by currents. Since these waters are always being warmed, they maintain high year round temperatures (21° - 30° C, 69.8° - 86° F) and are known as the Tropical Regions of the world's oceans. Certain sharks, such as the nurse shark , the tiger shark and the bull shark, are only comfortable in these warm waters where food is plentiful, so they remain there year-round without migrating.

Polar Regions

The waters near the north and south poles, called the Polar Regions, always stay at colder temperatures (below 5° C, 41° F). Sharks living here, such as the Greenland sleeper shark, are adapted to living under ice floes, and rarely voyage beyond their icy home.

Temperate Regions

The waters in between the tropical and polar regions are a mixture of warm and cold waters and have an intermediate temperature range which can vary a great deal as the seasons change. These waters are called Temperate Regions (10°-21°C, 50-69.8° F). Sharks that live here tend to migrate south in the winter and north in the summer as the seasons change and their food sources move up and down the coast.

Polar Region: If the ocean contained only pure, fresh water, the overall temperature range could extend all the way from 0° to 100° C (32° to 212° F). Because the salt in sea water has a warming influence, however, waters in the polar regions can still be liquid well below freezing. Amazingly several species of polar sharks -- like polar bears and penguins -- have adapted to live in icy cold waters where the temperature does not rise above 5° C (41° F). These include the Greenland sleeper shark, the pacific sleeper shark and the black dogfish shark. The Greenland sleeper shark lives under ice floes, preying on fish in the winter and rising to the surface to feed on seals and porpoises in the summer when the ice breaks.

Tropical Region: Hot tropical waters range from approximately 21° C (69.8° F) on up. The largest numbers of species and the largest populations of sharks live in the tropical region where the water temperature stays consistently warm. Tropical sharks include the huge filter-feeding whale shark, the great hammerhead shark, the nurse shark, the tiger shark, and the bull shark, which is found in both the ocean and in fresh water lakes in the tropics. Certain large species, such as the whale shark, range throughout the tropical region all over the world. Others, such as the nurse shark, are non-migratory and tend to stay in local warm water areas.

Nurse sharks prefer water temperatures between 20°-30°C (68°-86° F). Since they are prefer warm temperatures and feed on non-migratory animals such as spiny lobsters, small squid, and mollusks, nurse sharks stay in the same tropical locations all their lives. One of the mysteries of migration is that nurse sharks are occasionally found in New England in the summer, but not in the winter when the water temperature drops well below 20°C (68°F). Why are nurse sharks found at all in a region where water temperatures clearly drop below their range? Do some nurse sharks migrate? Do they hibernate like bears by swimming down into deeper waters? No one knows for certain where they are in the cold months of the year in New England.

Temperate Region: Waters in the temperate region generally range from 10°-21°C (50°-69.8°F) and rise up or down much more than polar or tropical waters. Large sharks that living in temperate waters include the great white shark, the shortfin mako shark, and the basking shark. These large temperate sharks can generate their own body heat and are therefore able to travel farther than smaller temperate sharks, which cannot. Although large temperate sharks will travel into tropical waters, they will swim only at depths where the temperature is in their preferred range. Smaller sharks are much more affected by heat and cold and stay within their limits.

Sandbar sharks like water temperature between about 15°-30°C (59°-86°F). In the Western North Atlantic, from New England to Florida and the Gulf of Mexico, sandbar sharks will begin to migrate north in the spring as water temperatures rise to 16° C (60.8°F) in the northern parts of their range. During the summer months, they will move up into the coastal New England area. When water temperatures begin to cool again in the fall, sandbars start their return trip to warmer southern waters along the coast of Florida, the Gulf of Mexico and the Caribbean.

Shortfin mako sharks live within a very narrow temperature range of approximately 17°-22°C (62.3°-71.6°F). In the North Atlantic part of their range, shortfin makos migrate from the Sargasso Sea in the south, up towards the northeastern coast of the U.S. in early summer as northern waters warm up. When water temperatures rise to 16°-17°C (60.8°-62.6°F), shortfin makos can be found along the continental shelf from Cape Hatteras, North Carolina to Georges Bank, off the coast of Massachusetts. In November and December, when water temperatures begin to go below 17°C (62.2°F), these sharks begin to return to warmer southern waters in the Sargasso Sea.

Ocean Depths: The depth of the ocean's water is another factor affecting water temperatures and where shark's live. Many species of sharks have adapted to live primarily in warm and shallow coastal waters along the continental shelves (usually no deeper than 650ft ), in the top few hundred meters of the open ocean (pelagic waters), or in very deep, cold waters near the bottom of the ocean. Examples of shallow water sharks are the nurse, the hammerhead, the sandbar, the great white and the tiger shark. Pelagic sharks are shortfin makos and whale sharks. Deep water sharks, such as catsharks, goblin sharks and megamouth sharks, stay in cold water all year round.