Chapter 1: The Disappearance of Hammerhead Sharks

Recent reports indicate troubling news about hammerhead sharks, which are experiencing significant population declines in various habitats. In the Gulf of California, the reduction in these majestic creatures is alarming, and contrary to earlier beliefs, it's not primarily due to the disturbances caused by boats or divers.

[Photo by Ben Phillips from Pexels]

Hammerhead sharks, part of the cartilaginous fish family, are easily recognized by their unique hammer-shaped heads. These sharks inhabit coastal waters of the Pacific, Atlantic, and Indian Oceans. Three species—scalloped hammerhead (Sphyrna lewini), great hammerhead (Sphyrna mokarran), and smooth hammerhead (Sphyrna zygaena)—are regarded as potentially dangerous to humans. Unfortunately, rampant fishing practices are severely depleting their numbers.

A recent study published in 'Marine Policy' detailed the alarming disappearance of a specific species of hammerhead from the southwestern region of the Gulf of California. Researchers pointed out that large-scale fishing is the primary driver behind this decline.

Analysis of 50 years' worth of data collected by divers revealed a staggering 97% drop in the population of scalloped hammerhead sharks. This decline was notably observed around the El Bajo underwater mountains, with the population in the Las Animas underwater mountains plummeting to zero. Both locations are situated off the Mexican coast.

[Photo by Walter Torres from Pexels]

The study highlighted that the Gulf of California has witnessed a general decrease in fish populations due to overfishing, with the scalloped hammerhead species being the most affected. Researchers noted, "This species is pelagic, forming large schools around underwater mountains where they seek refuge during the day."

The El Bajo underwater mountain, located near Espíritu Santo Island, and the Las Animas underwater mountain, near San José Island, have long been popular spots for divers hoping to observe S. lewini. The study utilized the insights of local divers to track changes in the population of S. lewini from 1970 to 2020.

Alarmingly, only five hammerhead sharks were observed around El Bajo in 2010, while zero sightings were recorded at Las Animas that same year. In stark contrast, 50 years earlier, divers commonly spotted around 1,000 sharks in the same region.

“This research underscores the necessity of gathering local ecological knowledge to document the declining populations of species, particularly S. lewini, which is currently classified as ‘critically endangered’ by the International Union for Conservation of Nature,” the researchers stated.

[Image by baechi from Pixabay]

There is an urgent need for enhanced protections against poaching and fishing practices that threaten this species. Adult scalloped hammerheads can reach lengths of 2.5 to 5 meters and weigh up to 400 kilograms. Their coloration ranges from olive to grayish-brown, with a white underside. These sharks primarily hunt at night, targeting smaller fish and invertebrates.

The primary reasons for the critical state of this species are their capture for fins and liver oil, as well as local fishing practices in the Caribbean where they are sought for their meat.

Kathryn Ayres, the lead author of the study, remarked that it was commonly believed the decline around underwater mountains was due to increasing boat noise and diver interference. However, their latest findings indicate that these factors had a minimal effect on the hammerheads' decline.

"In protected areas like the Revillagigedo archipelago in Mexico, divers still encounter substantial schools of hammerheads," Ayres noted. "Though these sharks tend to avoid divers now, they still thrive in those safeguarded environments." She expressed hope that more habitats for critically endangered species would receive similar protections.

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