The open ocean, a realm as vast as it is mysterious, harbors an array of enigmas. And none, arguably, is more captivating than the lives of its elusive sharks. Although one of the most iconic animals on the planet, much remains unknown of these predators. Over 450 million years of evolution has honed their roles as top predators in their respective ecosystems, playing pivotal roles in regulating fish communities and orchestrating nutrient cycling. The delicate harmony of healthy ecosystems is inextricably linked to healthy shark populations.
So, what happens when they vanish?
Despite their impressive evolutionary resilience thus far, sharks now confront their most formidable challenge: us. Specifically, our unsustainable fishing practices and the pressure it exerts on the ocean ecosystem. This threat looms large over the more than 500 shark species, officially among the most threatened vertebrates on the planet. In an intriguing juxtaposition of history, these ancient survivors of five mass extinctions now find themselves teetering on the brink of extinction. We must study them to protect them. Yet, our understanding of these creatures is curtailed by the immensity of the ocean and the inherent difficulties of studying them that comes with that. It’s worse than finding a needle in a haystack, it’s finding one in a haystack that bigger than the eye can see – and is underwater.
Critical to their protection is a comprehensive understanding of the distribution and behaviors of oceanic sharks. Undertaking epic odysseys spanning hundreds to thousands of kilometers across immense ocean basins, these predators have long intrigued scientists and adventurers alike. Yet, the secrets of their existence, their chosen habitats, and the reasons behind their journeys remain shrouded in obscurity. Yet University of Western Australia scientists have recently shed invaluable insights into the secret lives of one of these wide-ranging predators.
Meet the silky shark (Carcharhinus falciformis). Named for their smooth skin, these ocean wanderers epitomize the challenges faced by open ocean sharks — they are highly mobile, long-lived, and are slow to reproduce. Flourishing in tropical and sub-tropical waters, silky sharks symbolize the profound impact of industrial-scale fishing practices. Their numbers have dwindled globally as they are primarily targeted for their fins and meat while also becoming inadvertent casualties (bycatch) of tuna fisheries. Classified as “vulnerable to extinction” by the International Union for the Conservation of Nature (IUCN) in 2017, their plight is regulated under the Convention on International Trade in Endangered Species (CITES).
To unravel the mysteries of these oceanic behemoths, Dr. Jessica Meeuwig and PhD candidate Shona Murra from the University of Western Australia deployed Baited Remote Underwater Video Systems (BRUVS) into the blue waters across the Atlantic, Pacific, and Indian Oceans from 2012 to 2020. Armed with video cameras and bait, these systems provide a window into the lives of marine predators, capturing behaviors as they drift with ocean currents at a depth of 32 feet (10 meters). Amidst the waves, the duo tracked the presence of silky sharks, uncovering a fascinating love affaird with a specific underwater feature: seamounts.
Underwater mountains rising from the ocean depths, these geological features stand out as oases of topographic complexity in the otherwise desert-like conditions in our open oceans. The scientists found that closer proximity to these seamounts correlated with higher frequencies and numbers of silky sharks, illuminating these submerged giants as hotspots of marine biodiversity. And their significance extends beyond being mere landmarks, as they provide essential resources for feeding, breeding, and resting for sharks, tuna, whales, and other migratory wildlife. Intriguingly, their observations unveiled a trend — smaller silky sharks tend to congregate closest to seamounts, suggesting these underwater pinnacles provide a rich nursery for these rapidly growing youngsters.
However, our footprint casts a shadow even over these remote domains. The closer the team’s work ventured to coastal ports, the starker the decline in silky shark populations. The implications are profound: sharks near human populations were smaller and less abundant, a consistent pattern indicative of fishing impact. And this alarming trend extends beyond silky sharks, reflecting the broader decline faced by open ocean sharks, including hammerhead, sandbar, tiger, and whale sharks. This, the team stresses, underlines the pervasive and dire impact of human activity on oceanic sharks, underscoring the urgent need for sanctuaries where these creatures can thrive, sheltered from exploitation.
“The need for improved protection for oceanic wildlife is well-recognised and marine protected areas are a key tool to deliver this protection. In 2022, under the Convention on Biological Diversity, nearly every country in the world committed to protect 30% of their oceans by 2030,” the researchers wrote on a Conservation piece. “In 2023, the High Seas Treaty was ratified by the 193 member states of the United Nations, paving the path towards strong and effective protection of the vast swaths of ocean beyond national jurisdiction. Given that less than 2.9% of our oceans are currently highly protected, such opportunities are essential.”
They hope their research serves as a compass, guiding stakeholders toward effective strategies for safeguarding our open oceans. As marine protected areas gain traction, focusing on habitats frequented by threatened species like silky sharks becomes paramount. Seamounts, shimmering oases amidst the open ocean expanse, offer a fitting focal point for marine protection efforts.