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Context

• Researchers have found that Goa has the highest percentage of ‘elasmobranch’ (shark and ray) meat selling restaurants (35.8 per cent), followed by Tamil Nadu (34.6 per cent) and Maharashtra (4.6 per cent).

Elasmobranchs

• Elasmobranchs represent a subclass of cartilaginous fish that includes sharks, rays, and skates. These marine creatures play a crucial role in maintaining the balance of marine ecosystems. Here's a comprehensive overview of elasmobranchs for UPSC Prelims:

Taxonomy and Diversity:

• Subclass Elasmobranchii: Elasmobranchs belong to the subclass Elasmobranchii within the class Chondrichthyes, which also includes chimaeras.
• Sharks, Rays, and Skates: Elasmobranchs encompass a diverse group, with over 1,200 known species, including well-known apex predators like sharks and bottom-dwelling rays and skates.

Morphological Features:

• Cartilaginous Skeleton: Elasmobranchs have skeletons made of cartilage rather than bone, making them more flexible and lighter than bony fish.
• Dermal Denticles: The skin of elasmobranchs is covered in dermal denticles, which are tooth-like structures that reduce drag and enhance swimming efficiency.

Ecological Significance:

• Apex Predators: Many shark species are apex predators, playing a crucial role in regulating the populations of prey species and maintaining overall ecosystem health.
• Benthic Species: Rays and skates are primarily bottom-dwelling species that contribute to the ecological balance of the seafloor.

Distribution and Habitat:

• Global Distribution: Elasmobranchs are found in various marine environments, from coastal areas to the open ocean, and from shallow waters to the deep sea.
• Adaptability: Some elasmobranchs can tolerate a wide range of temperatures and salinities, allowing them to inhabit diverse habitats.

Reproduction and Life History:

• Viviparity and Oviparity: Elasmobranchs exhibit various reproductive strategies, including viviparity (live birth) and oviparity (egg-laying), depending on the species.
• Slow Growth and Longevity: Many elasmobranch species have slow growth rates and long lifespans, contributing to their vulnerability to overfishing.

Threats and Conservation:

• Overfishing: Elasmobranchs are vulnerable to overfishing due to their slow reproductive rates and susceptibility to bycatch.
• Conservation Measures: International and national conservation initiatives focus on implementing sustainable fishing practices, protecting critical habitats, and regulating the trade of elasmobranch products.

Economic Importance:

• Fisheries: Elasmobranchs are targeted for their meat, fins (for shark fin soup), and other body parts, contributing to global fisheries.
• Ecotourism: Shark tourism, centered around observing live sharks in their natural habitat, has become an increasingly important economic activity and conservation tool.

Human-Wildlife Conflict:

• Shark Attacks: Rare incidents of shark attacks on humans sometimes lead to conflicts and negative perceptions of these creatures.
• Mitigation Strategies: Educational programs and research aim to reduce the incidence of attacks and improve human understanding of elasmobranch behavior.

PRACTICE QUESTION Question: Which of the following statements regarding elasmobranchs is/are correct? 1.Elasmobranchs belong to the class Osteichthyes, characterized by a bony skeleton. 2.The skin of elasmobranchs is covered in scales, similar to those found in bony fish. 3.Rays and skates are primarily pelagic species, dwelling in the open ocean. 4.Elasmobranchs exhibit various reproductive strategies, including viviparity and oviparity. Choose the correct answer from the options below: A. 1 and 3 only B. 2 and 4 only C. 1 and 4 only D. 2 and 3 only Correct Answer: C. 1 and 4 only Explanation: Elasmobranchs belong to the class Osteichthyes, characterized by a bony skeleton. Incorrect: Elasmobranchs belong to the subclass Elasmobranchii within the class Chondrichthyes, characterized by a cartilaginous skeleton. The class Osteichthyes comprises bony fish. The skin of elasmobranchs is covered in scales, similar to those found in bony fish. Incorrect: The skin of elasmobranchs is not covered in traditional scales. Instead, it is covered in dermal denticles, tooth-like structures that reduce drag and enhance swimming efficiency. This is a unique feature distinguishing them from bony fish. Rays and skates are primarily pelagic species, dwelling in the open ocean. Incorrect: Rays and skates are primarily benthic species, meaning they dwell on or near the ocean floor. They are adapted to life on the seafloor and are not considered pelagic species. Elasmobranchs exhibit various reproductive strategies, including viviparity and oviparity. Correct: Elasmobranchs indeed exhibit various reproductive strategies. Some species are viviparous, giving birth to live young, while others are oviparous, laying eggs. This diversity in reproductive strategies is characteristic of elasmobranchs. Therefore, the correct answer is C. 1 and 4 only.