The saltwater sharks, also known as marine sharks, play a crucial role in marine ecosystems by acting as top predators in the food chain. They regulate the populations of other species, maintaining the ecological balance and health of the oceans. By controlling prey populations, this class of sharks prevents the overexploitation of certain resources and helps preserve biodiversity. Additionally, they contribute to the elimination of weak or sick individuals, promoting the vitality of marine populations.
Índice de Contenidos
- Importance of Sharks in Marine Ecosystems
- Diversity and Distribution of Marine Sharks
- Species of Marine Sharks: Classification
- Physiology and Adaptations of Marine Sharks
- Habitats and Geographic Distribution of Marine Sharks
- Ecological Roles of Sharks in the Ocean
- Taxonomic Groups of Sharks, Rays, and Manta Rays
- Interactions Between Humans and Sharks in the Sea
- Reproduction and Life Cycle of Marine or Saltwater Sharks
- Frequently Asked Questions (FAQ)
- See Also
Importance of Sharks in Marine Ecosystems
Sharks play a crucial role in marine ecosystems, being powerful and very agile animals. They are vital for the maintenance of the ecosystem, and their conservation is key to maintaining the health of the planet. There are different species of sharks, with the most numerous being those that live in the sea. These sharks are the largest and longest-lived.
Diversity and Distribution of Marine Sharks
Saltwater sharks are incredibly diverse, with more than 500 species varying in size, shape, and behavior. From the gigantic whale sharks to the tiny lantern sharks, these creatures inhabit all the world's oceans, from warm tropical waters to the cold polar depths, as seen with the deep-sea sharks. Their adaptability allows them to occupy a wide range of habitats, from coral reefs and mangroves to the vast expanses of the open ocean. They are much more distributed than freshwater or river sharks.
Species of Marine Sharks: Classification
Order Carcharhiniformes
The order Carcharhiniformes, also known as reef sharks or ground sharks, includes some of the most recognizable species. Tiger sharks (Galeocerdo cuvier) are known for their aggressiveness and varied diet, while hammerhead sharks (family Sphyrnidae) stand out for their distinctive hammer-shaped heads, which enhance their vision and ability to detect prey. These sharks are found in warm and tropical waters, often near coral reefs.
Main Families and Species
- Carcharhinidae (Requiem sharks)
- Carcharhinus leucas (Bull shark) (Saltwater and freshwater)
- Carcharhinus limbatus (Blacktip shark) (Saltwater)
- Galeocerdo cuvier (Tiger shark) (Saltwater)
- Prionace glauca (Blue shark) (Saltwater)
- Scyliorhinidae (Cat sharks)
- Scyliorhinus canicula (Lesser spotted dogfish) (Saltwater)
- Triakidae (Hound sharks)
- Triakis semifasciata (Leopard shark) (Saltwater)
- Hemigaleidae (Weasel sharks)
- Hemigaleus microstoma (Weasel shark) (Saltwater)
- Leptochariidae (Barbeled houndshark)
- Leptocharias smithii (Barbeled houndshark) (Saltwater)
- Proscylliidae (Finback catsharks)
- Proscyllium habereri (Finback catshark) (Saltwater)
- Pseudotriakidae (False catsharks)
- Pseudotriakis microdon (False catshark) (Saltwater)
- Sphyrnidae (Hammerhead sharks)
- Sphyrna lewini (Common hammerhead shark) (Saltwater)
Order Lamniformes
The order Lamniformes includes iconic species such as the great white shark (Carcharodon carcharias), the mako shark (Isurus spp.), and the basking shark (Cetorhinus maximus). These sharks are known for their size and speed, with the mako shark being the fastest of all sharks. Lamniformes are found in all the world's oceans, from coastal waters to deep pelagic zones. They are top predators and play a crucial role in maintaining the balance of marine ecosystems.
Main Families and Species
- Alopiidae (Thresher sharks)
- Alopias pelagicus (Pelagic thresher shark) (Saltwater)
- Alopias superciliosus (Bigeye thresher shark) (Saltwater)
- Alopias vulpinus (Common thresher shark) (Saltwater)
- Cetorhinidae
- Cetorhinus maximus (Basking shark) (Saltwater)
- Lamnidae (Mako and white sharks)
- Carcharodon carcharias (White shark) (Saltwater)
- Isurus oxyrinchus (Shortfin mako shark) (Saltwater)
- Isurus paucus (Longfin mako shark) (Saltwater)
- Lamna ditropis (Salmon shark) (Saltwater)
- Lamna nasus (Porbeagle shark) (Saltwater)
- Megachasmidae
- Megachasma pelagios (Megamouth shark) (Saltwater)
- Mitsukurinidae
- Mitsukurina owstoni (Goblin shark) (Saltwater)
- Odontaspididae
- Odontaspis ferox (Smalltooth sand tiger shark) (Saltwater)
- Odontaspis noronhai (Bigeye sand tiger shark) (Saltwater)
- Pseudocarchariidae
- Pseudocarcharias kamoharai (Crocodile shark) (Saltwater)
Order Orectolobiformes
The order Orectolobiformes, also known as carpet sharks, includes the whale shark (Rhincodon typus), the largest fish in the world. These sharks are generally docile and feed primarily on plankton and small fish. Nurse sharks and carpet sharks are other notable species within this order, known for their distinctive skin patterns and sedentary behavior. They are found in warm and tropical waters, frequently in coral reefs and coastal areas.
Main Families and Species
- Ginglymostomatidae (Nurse sharks)
- Ginglymostoma cirratum (Nurse shark) (Saltwater)
- Hemiscylliidae (Longtail carpet sharks)
- Hemiscyllium ocellatum (Epaulette shark) (Saltwater)
- Orectolobidae (Wobbegong sharks)
- Orectolobus maculatus (Spotted wobbegong) (Saltwater)
- Rhincodontidae
- Rhincodon typus (Whale shark) (Saltwater)
- Stegostomatidae
- Stegostoma fasciatum (Zebra shark) (Saltwater)
- Parascylliidae (Collared carpet sharks)
- Parascyllium variolatum (Varied carpetshark) (Saltwater)
- Brachaeluridae (Blind sharks)
- Brachaelurus waddi (Blind shark) (Saltwater)
Order Squaliformes
The order Squaliformes includes a variety of sharks, including the Greenland shark (Somniosus microcephalus), known for its extreme longevity and habitat in the cold Arctic waters. Lantern sharks, which emit light to camouflage and attract prey, also belong to this order. Cookiecutter sharks (Isistius brasiliensis) are famous for biting large chunks of flesh from much larger animals. These sharks inhabit the depths of the ocean to surface waters in different regions of the world.
Main Families and Species
- Centrophoridae (Gulper sharks)
- Centrophorus granulosus (Gulper shark) (Saltwater)
- Dalatiidae (Kitefin sharks)
- Isistius brasiliensis (Cookiecutter shark) (Saltwater)
- Etmopteridae (Lantern sharks)
- Etmopterus spinax (Velvet belly lanternshark) (Saltwater)
- Oxynotidae (Rough sharks)
- Oxynotus centrina (Roughshark) (Saltwater)
- Somniosidae (Sleeper sharks)
- Somniosus microcephalus (Greenland shark) (Saltwater)
- Squalidae (Dogfish sharks)
- Squalus acanthias (Spiny dogfish) (Saltwater)
Order Hexanchiformes
Includes the most primitive sharks, such as the sixgill shark and the frilled shark, which are found in deep, cold waters.
Main Families and Species
- Hexanchidae (Cow sharks)
- Hexanchus griseus (Bluntnose sixgill shark) (Saltwater)
- Chlamydoselachidae (Frilled sharks)
- Chlamydoselachus anguineus (Frilled shark) (Saltwater)
Order Heterodontiformes
Sharks of the order Heterodontiformes, also known as bullhead sharks or horn sharks, have a distinctive appearance with a wide head, prominent eyes, and dorsal fins with spines. These sharks are small to medium-sized with robust, short bodies. They are known for their benthic habits, primarily inhabiting shallow, warm, and tropical waters.
Main Families and Species
- Heterodontidae (Bullhead sharks or horn sharks)
- Heterodontus francisci (Horn shark) (Saltwater)
- Heterodontus portusjacksoni (Port Jackson shark) (Saltwater)
- Heterodontus galeatus (Crested bullhead shark) (Saltwater)
- Heterodontus ramalheira (African bullhead shark) (Saltwater)
- Heterodontus japonicus (Japanese bullhead shark) (Saltwater)
- Heterodontus mexicanus (Mexican bullhead shark) (Saltwater)
Order Pristiophoriformes
Sharks of the order Pristiophoriformes, commonly known as sawsharks, are easily recognizable by their long, flattened, saw-like snouts with sharp teeth along the edges. This serrated snout is used for capturing prey and defense. They have a slender appearance and often live in deep waters. Known for their benthic habits, they can be found in both tropical and temperate waters.
Main Families and Species
- Pristiophoridae (Sawsharks)
- Pristiophorus cirratus (Longnose sawshark) (Saltwater)
- Pristiophorus nudipinnis (Common sawshark) (Saltwater)
- Pristiophorus schroederi (Bahamas sawshark) (Saltwater)
- Pristiophorus japonicus (Japanese sawshark) (Saltwater)
- Pristiophorus delicatus (Tropical sawshark) (Saltwater)
- Pristiophorus lanae (Lana's sawshark) (Saltwater)
Physiology and Adaptations of Marine Sharks
Cartilaginous Structure
Sharks have a skeleton made of cartilage instead of bone. This material is lighter and more flexible, allowing for greater agility and energy savings while swimming.
Sensory Adaptations: Lateral Line and Ampullae of Lorenzini
Sharks possess a lateral line that allows them to detect movements and vibrations in the water, crucial for locating prey. The ampullae of Lorenzini are sensory organs that detect electric fields generated by other animals, aiding in hunting and navigation.
Hunting and Feeding Strategies
Shark hunting strategies vary by species. Some, like great white sharks, ambush their prey from below, while others, like hammerhead sharks, use their hammer-shaped heads to immobilize their prey. There are also filter feeders like the whale shark that feed on plankton.
Habitats and Geographic Distribution of Marine Sharks
Coastal Sharks vs. Open Water Sharks
Coastal sharks live near shores and reefs, where they find abundant food and shelter. Open water sharks, like the blue shark, inhabit the pelagic ocean and are adapted for long migratory journeys.
Adaptations to Different Depths and Temperatures
Sharks have specific adaptations to survive in various depths and temperatures. For example, Greenland sharks inhabit cold, deep waters, while reef sharks prefer warm, shallow waters.
Regions of the World with the Greatest Shark Diversity
Tropical and subtropical regions, such as the Indo-Pacific and the Caribbean, host the greatest diversity of shark species due to the variety of available habitats and abundant food supply.
Ecological Roles of Sharks in the Ocean
Sharks, rays, and skates play crucial ecological roles in marine ecosystems. Below are some of the key functions they perform:
Apex Predators
Sharks, especially larger species like great whites and tiger sharks, act as apex or top predators. As apex predators, they help regulate populations of other marine species by controlling the abundance of their prey and maintaining balance in various food webs.
Trophic Cascade Effects
The presence of sharks in an ecosystem can generate cascading effects throughout the food web. Their predatory behavior influences the distribution and behavior of prey species, which in turn affects the abundance and composition of lower trophic levels.
Mesopredator Control
Sharks help control populations of mesopredators, such as smaller sharks and rays. By preying on these mesopredators, they prevent them from becoming too abundant and exerting excessive predation pressure on smaller prey species.
Regulating Prey Behavior
The mere presence of sharks in an area can influence the behavior and movements of their prey. This can lead to changes in prey distribution, feeding patterns, and habitat use, causing cascading effects throughout the ecosystem.
Nutrient Cycling
When sharks feed on their prey, they contribute to nutrient cycling within marine ecosystems. Nutrients obtained from prey are redistributed through shark excretions, facilitating the transfer of vital nutrients between different habitats and supporting ecosystem productivity.
Habitat Structuring
Rays and manta rays, with their feeding and foraging behaviors, can influence the structure and composition of benthic habitats. By disturbing sediments while feeding, they create patches of bare substrate, affecting the diversity and distribution of benthic organisms.
Influence on the Evolution of Prey Species
The predation pressure exerted by sharks, rays, and manta rays can shape the evolutionary adaptations of their numerous prey species. Prey may develop behavioral, morphological, or physiological traits to avoid predation, leading to the development of unique adaptations within ecosystems.
The ecological functions performed by sharks, rays, and manta rays contribute significantly to the overall health and functioning of marine ecosystems. Protecting these species is crucial for maintaining balanced and resilient marine communities.
Taxonomic Groups of Sharks, Rays, and Manta Rays
Sharks belong to the same taxonomic group Chondrichthyes, which also includes rays and manta rays, consisting of cartilaginous fish.
Sharks belong to the animal kingdom, comprising multicellular and eukaryotic organisms, and are chordates. They possess a notochord, a dorsal nerve cord, and pharyngeal slits at some stage of their life cycle. Sharks are a class of fish known as cartilaginous fish, whose skeletons are made of cartilage instead of bone.
- Kingdom: Animalia
- Phylum: Chordata
- Class: Chondrichthyes
- Subclass: Elasmobranchii – Includes both sharks and rays.
- Order: There are several orders within sharks, including Carcharhiniformes (requiem sharks), Lamniformes (mackerel sharks), and Orectolobiformes (carpet sharks).
- Family, Genus, and Species: There are numerous families, genera, and species of sharks. Examples include the great white shark (Carcharodon carcharias), the tiger shark (Galeocerdo cuvier), and hammerhead sharks (Sphyrna spp.).
Rays
Rays share the same classification as sharks in the kingdom Animalia, phylum Chordata, and class Chondrichthyes. Rays also form part of the subclass Elasmobranchii.
- Order: Rajiformes – Includes a diverse range of ray species.
- Family, Genus, and Species: Within the order Rajiformes, there are various families, genera, and species of rays. Examples include manta rays (Manta spp.), whiprays (family Dasyatidae), and eagle rays (family Myliobatidae).
Manta Rays
Manta rays share the same classification as sharks and rays in the kingdom Animalia, phylum Chordata, class Chondrichthyes, and subclass Elasmobranchii.
- Order: Rajiformes – Manta rays are part of the same order Rajiformes as rays.
- Family, Genus, and Species: Within the order Rajiformes, manta rays belong to various families, genera, and species. Examples include the common skate (Dipturus batis), the thorny skate (Amblyraja radiata), and the clearnose skate (Raja eglanteria).
It is worth noting that this classification is a simplified view, as there are many species within each group, each with its own taxonomic categorization. Taxonomy is a dynamic field, and new discoveries and research can lead to changes in classifications over time.
Interactions Between Humans and Sharks in the Sea
Debunking Shark Attacks
Shark attacks on humans are extremely rare and often due to the shark's confusion. Most sharks do not see humans as prey and prefer to avoid them.
Impact of Humans on Shark Populations
Overfishing and hunting of sharks for their fins have led to a significant decline in their populations. Habitat destruction and pollution also negatively affect these species.
Conservation Efforts and Habitat Protection
Various global initiatives exist to protect sharks, including marine protected areas, fishing regulations, and awareness campaigns to reduce the shark fin trade and promote sustainable fishing practices.
Reproduction and Life Cycle of Marine or Saltwater Sharks
Reproductive Methods: Oviparous, Viviparous, and Ovoviviparous
Sharks employ different reproductive methods. Oviparous sharks lay eggs that hatch outside the mother's body, viviparous sharks give birth to live young, and ovoviviparous sharks have eggs that hatch inside the mother's body before birth.
Embryonic Development and Parental Care
Embryonic development varies by species, with gestation periods ranging from months to over a year. Generally, sharks do not exhibit parental care once the young are born.
Growth Rate and Longevity
The growth rate and longevity of sharks depend on the species. Some sharks can live over 70 years, like the Greenland shark, while others have shorter lifespans. Growth is generally slow, making sharks vulnerable to overfishing.
Frequently Asked Questions (FAQ)
What is the largest saltwater shark?
The largest saltwater shark is the whale shark (Rhincodon typus). It can grow to be over 12 meters long (40 feet) and, despite its size, feeds primarily on plankton and small fish, being harmless to humans.
Are sharks dangerous to humans?
Sharks are not inherently dangerous to humans. While some shark attacks do occur, they are extremely rare and often result from shark confusion. Most sharks do not see humans as prey and prefer to avoid them.
Can saltwater sharks survive in freshwater?
Most saltwater sharks cannot survive in freshwater due to their need to maintain a balance of salt and water in their bodies. However, some species like the bull shark (Carcharhinus leucas) have the ability to adapt to both types of water and can be found in rivers and freshwater lakes.
How do saltwater sharks reproduce?
Saltwater sharks use various reproductive methods. Oviparous sharks lay eggs that hatch outside the mother's body, viviparous sharks give birth to live young, and ovoviviparous sharks have eggs that hatch inside the mother's body before birth. These methods vary among different shark species.