Pelagic sharks registered the largest reduction in numbers whereas demersal sharks did not show much decline.
Human impact has adversely impacted the marine diversity is such a way that it has witnessed a steep decline since the mid-Holocene age, found a study that analysed fossilized shark scales. The time period begun 10,000 years ago.
Sharks like other cartilaginous marine animals have sharp tooth-scaled scales on their body as a protective mechanism for microorganisms making their body host and to move through water. The study used such deposits of dermal denticles of sharks. There are currently over 500 species of sharks.
Researchers collected denticles from the mid-Holocene reef and modern day reef and compared them. Five morphotypes of dermal denticles from aa ecological group of sharks were identified and found that almost all species of sharks witnessed a decline in their population. Shark abundance in the mid-Holocene was nearly thrice higher than the present-day reefs.
Pelagic sharks registered the largest reduction in numbers whereas demersal sharks did not show much decline. Benthic sharks, living in bottom showed more abundance in number than pelagic sharks that remain attached to the surface like the fast swimming requiem and hammerhead sharks that live near the shore.
Researchers feel sharks of the yesteryears could have been larger, resulting in more denticle accumulation.
How overfishing caused depletion in shark population
Over fishing has resulted in entirely exterminating sharks from several reefs, found a study published in 2020. Early 20th or 19th C says seas teemed with sharks and even early second millennium CE archaeological records also show evidence of shark teeth. Not just sharks, the post industrialisation period saw substantial degradation of other marine carnivores as well before coral diseases and bleaching .
Modern-day Panamanian fisheries catching pelagic sharks is also another factor for depletion of shark population.
Depletion of numbers of nurse sharks that live close to the bottom of the ocean and have no monetary value can be attributed to coastal development, agriculture, land clearing that reduces oxygen content in air, and bleaching, observed across the Caribbean sea.
How depletion of sharks will have a bigger ecological impact is being studied. According to the author, such studies that dive into ancient fossils of shark remians and find human impact can set robust targets for biodiversity restoration in these areas that saw the depletion.