Sharks, ancient marine predators, have long fascinated humanity. Their presence in diverse marine ecosystems sparks curiosity about their global distribution. Their global distribution highlights their remarkable evolutionary success and ability to thrive across varied environments.
Global Presence
Sharks are found in all five of the world’s major oceans: the Pacific, Atlantic, Indian, Southern, and Arctic. While sharks are ubiquitous, individual species have more specific geographical ranges. There are over 500 recognized shark species, each with unique habitat preferences.
Factors Shaping Their Habitats
Water temperature is a primary factor influencing where different shark species reside, as it affects their metabolism, digestion, and reproduction. Sharks are often categorized as tropical, temperate, or polar based on their preferred surface water temperatures. Larger shark species may undertake extensive migrations to remain within optimal temperature ranges, while smaller species tend to be more restricted. Rising ocean temperatures due to climate change can lead to shifts in these established habitats.
The depth of the ocean also plays a significant role in shark distribution. Sharks inhabit waters ranging from the sunlit surface to depths exceeding 2,000 meters. Light levels, pressure, and prey availability vary considerably with depth, influencing which species can survive. Food availability, a key factor, influences foraging; their diets range from microscopic plankton to large marine mammals. Coastal sharks find food locally, while some oceanic sharks travel great distances to nutrient-rich feeding grounds.
Ocean currents further shape shark habitats by aiding navigation, facilitating migrations, and concentrating prey. These currents can create upwelling events, bringing colder, nutrient-rich water to the surface, influencing shark movements and sometimes posing thermal challenges. Salinity and dissolved oxygen levels are additional environmental variables affecting shark distribution, particularly in coastal and estuarine environments.
Adaptations and Specific Environments
Sharks have developed remarkable adaptations to survive in a vast array of marine environments. In frigid polar waters, the Greenland shark exemplifies this adaptation, preferring cold temperatures and inhabiting depths from 100 to 1,200 meters. This species is found in Arctic and sub-Arctic regions.
Deep-sea environments host over half of all known shark species, living in perpetual darkness. Examples include the goblin shark, found in the Pacific, Atlantic, and Indian Oceans, typically around 1,200 meters deep, known for its protrusible jaws. The frilled shark inhabits depths between 118 meters and 1.2 kilometers globally. The cookiecutter shark occupies warm oceanic waters worldwide, usually between 1 and 3.7 kilometers deep. The Portuguese dogfish has been recorded at depths exceeding 12,000 feet.
While the vast majority of sharks are strictly marine, a few species exhibit a rare tolerance for brackish or freshwater. The bull shark is a prominent example, known for its ability to inhabit both saltwater and freshwater, traveling thousands of kilometers up rivers. This adaptability highlights the evolutionary flexibility of sharks, enabling them to colonize nearly every aquatic niche.