Shark
Overview
Sharks are marine organisms belonging to the class Chondrichthyes (cartilaginous fish), ancient fish that have existed on Earth since the Devonian period about 400 million years ago. Currently, approximately 500 species are known worldwide, ranging in size from the dwarf lanternshark, less than 20 cm, to the whale shark, over 12 m. As apex predators in the marine ecosystem, sharks play a crucial role in maintaining the balance of the food chain.
Main Content
Classification and Evolution
Sharks have skeletons made of cartilage and have followed a different evolutionary path from bony fish. The ancestors of modern sharks are estimated to have appeared about 420 million years ago, making them an older group than dinosaurs. Major taxonomic groups include the Carcharhiniformes, Lamniformes, Orectolobiformes, and Rajiformes (rays).
Anatomical Features
- Cartilaginous Skeleton: Light and flexible, advantageous for fast movement and maneuverability.
- Skin: Covered with placoid scales (dermal denticles), which reduce friction and enhance hydrodynamic efficiency.
- Teeth: Arranged in multiple rows and continuously replaced throughout life. Tooth shape varies by species.
- Sensory Organs: Developed with ampullae of Lorenzini (electroreception), lateral line (vibration detection), and olfaction (excellent sense of smell).
- Respiration: Absorbs oxygen through gills; some species may suffocate if they stop swimming.
Ecology and Behavior
Most sharks are carnivorous, feeding on fish, marine mammals, crustaceans, and cephalopods. Whale sharks and basking sharks are filter feeders that strain plankton. Many shark species are solitary, but some travel or hunt in groups. Reproductive methods vary among oviparity, ovoviviparity, and viviparity, with long gestation periods and few offspring, leading to slow population recovery.
Relationship with Humans
Sharks are often perceived as objects of fear through mass media such as the film 'Jaws', but actual shark attacks on humans are very rare. Globally, about 70-100 shark attacks are reported annually, with only 5-10 fatalities. In contrast, approximately 100 million sharks are killed by humans each year.
Recent Trends
As of 2024-2025, international interest in shark conservation is increasing. Shark finning for shark fin soup has been banned in many countries, and CITES (Convention on International Trade in Endangered Species) has added several shark species to its protected lists. Rising sea temperatures due to climate change are causing shifts in shark habitats and changes in reproductive patterns. Additionally, shark diving as part of ecotourism is gaining popularity, contributing to local economies. In the scientific community, research on shark immune systems and cancer resistance is actively underway, with potential applications in human medicine.
Related Topics
- [[Cartilaginous fish]]
- [[Marine ecosystem]]
- [[Endangered species]]
- [[Whale shark]]
- [[Great white shark]]
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