A 71% Collapse in Shark Populations
Shark populations have plummeted by 71% since 1970. This staggering decline is driven primarily by shark finning and overfishing.
Anatomy of an Ancient Predator
Sharks are predatory cartilaginous fishes belonging to the class Chondrichthyes. The Shark Research Institute defines them as fish with internal skeletons made of flexible cartilage instead of bone. These animals are characterized by dermal denticles, a ribless endoskeleton, pectoral fins that are not fused to the head, and five to seven gill slits on each side. Within the group Elasmobranchii, the Shark Research Institute notes there are eight orders of sharks.
From the Deep Sea to Freshwater Rivers
These fish inhabit all seas at depths reaching 2,000 meters. While most species avoid freshwater, the Ganges shark is an exception, living only in freshwater environments. Bull sharks and river sharks are more versatile, found in both freshwater and seawater. Size varies significantly across the species, ranging from the 17-centimeter dwarf lanternshark to the whale shark, which can reach approximately 18.8 meters.
Ecological Roles and Feeding Habits
Ecologically, some species serve as apex predators. This group includes the hammerhead, mako, thresher, tiger, bull, and great white sharks. Others, such as the basking shark and whale shark, are filter-feeding planktivores.
Evolutionary Origins
The evolutionary history of shark-like chondrichthyans dates back to the Devonian Period, 419 to 359 million years ago. The earliest confirmed modern sharks, known as Selachii, appeared around 200 million years ago during the Early Jurassic. Agaleus remains the oldest known member of this group.
The Linguistic Roots of a Name
Until the 16th century, mariners referred to these creatures as “sea dogs.” The modern term “shark” likely derives from the Dutch word schurk, which translates to “scoundrel” or “villain.”
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