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Hidden giants beneath the waves
Towering underwater mountains, known as seamounts, rise from the ocean floor, creating hotspots of marine biodiversity. These geological formations, often remnants of extinct volcanoes, support thriving ecosystems-particularly for sharks, which gather in unprecedented numbers around their peaks.
Seamounts: Oases of the deep
Seamounts are underwater mountains that soar at least 1,000 meters (3,300 feet) from the seafloor. Some feature craters, ridges, or flat plateaus, while others breach the surface to form islands. These structures act as ecological crossroads, where deep-sea and open-water species converge across the food chain.
Scientists estimate over 100,000 seamounts exist worldwide, yet fewer than 0.1% have been explored. Recent expeditions, however, reveal their critical role in sustaining marine life. During a 2025 Atlantic Ocean survey, researchers documented 41 times more shark biomass near seamounts than in surrounding waters, alongside five times the diversity of large predatory fish.
The mystery of shark aggregations
Why do sharks flock to seamounts? Theories include their use as navigational landmarks, shelters, or feeding grounds. Ali Mashayek, a climate dynamics expert at the University of Cambridge, notes that seamounts generate unique magnetic fields due to their iron-rich volcanic rock, which may guide migratory species like sharks and whales.
Sam Weber, a marine ecologist at the University of Exeter, proposes two hypotheses: the oasis theory, where seamounts generate their own energy via nutrient upwellings, and the hub theory, where predators gather after foraging elsewhere. His research near Ascension Island supports both ideas. Turbulent currents around seamounts push nutrient-rich water upward, fueling phytoplankton blooms that attract larger species. Meanwhile, sharks like silky and Galapagos sharks appear to use seamounts as rest stops during migrations.
"Seamounts have a really strong magnetic signature that a lot of these species are attuned to. We're interested to find out whether they use them as stepping stones along their migratory corridor."
Sam Weber, University of Exeter
Threats and conservation efforts
Despite their ecological importance, seamounts face severe threats from industrial fishing, particularly bottom trawling. This destructive practice drags weighted nets across the seafloor, decimating slow-growing corals and sponges that take centuries to recover. Lydia Koehler, an ocean governance expert at Plymouth University, warns that bycatch-unintentional shark catches-kills hundreds of millions of sharks annually.
Progress is being made, however. In 2025, the International Union for Conservation of Nature adopted a resolution calling for a global ban on bottom trawling over seamounts by 2026. Portugal's Gorringe Seamount, one of Europe's tallest underwater mountains, was designated a protected marine area in 2025 after a scientific expedition highlighted its biodiversity. Ascension Island's entire Exclusive Economic Zone has been closed to commercial fishing since 2019.
A halo of life
Seamounts influence marine life far beyond their summits. Weber's team found a "halo" of increased predator activity extending up to 6 kilometers (3.7 miles) into the open ocean-expanding at night and contracting by day. Some sharks, like silky sharks, traveled hundreds of kilometers from seamounts but remained "site-attached," returning regularly.
These findings underscore the need for large-scale protection. "When designing marine reserves, we must think bigger than just the summit," Weber says. "Seamounts are irreplaceable oases, and their destruction has cascading effects on the entire ocean."
The path forward
While banning bottom trawling is a critical step, Weber argues for stricter measures, including bans on pelagic longline fishing near seamounts. "Predators like sharks have been hammered by commercial fishing," he says. "Protecting the whole ecosystem-not just parts of it-is essential for their survival."
