The gill plate trade: why manta rays are hunted

Manta rays are hunted primarily for their dried gill plates, which are sold for unregulated traditional remedies despite a complete lack of accepted clinical evidence supporting their health claims.

In the dark ocean waters, massive shadowy forms glide beneath the illuminated surface.

According to the IUCN Red List assessment, growing commercial demand for dried gill plates transformed opportunistic catches into targeted manta fisheries across several maritime nations.

Demand for Manta Gill Plates

Manta gill plates are harvested, dried, and sold for use in unregulated traditional remedies. Research cited by the Marine Megafauna Foundation highlights that there is no accepted clinical evidence supporting any of the health claims made for manta gill plates. To counter overexploitation, international trade controls have been established: a CITES Appendix II listing requires permits for international trade in manta products. Furthermore, peer-reviewed manta tourism valuation studies demonstrate that a living manta ray at a well-managed viewing site generates far more long-term local income than a single catch.

Manta Ray Biology and Intelligence

Manta rays, including the Hawaiian reef manta ray (Mobula alfredi), are filter feeders that consume zooplankton. Typical adult reef mantas feature wingspans ranging from 8 to 16 feet (reaching up to approximately 16 feet). They possess specialized cephalic fins—often called "horns"—that unfurl to funnel plankton into their mouth while feeding and roll up tight when cruising. Brain research shows that mantas have the largest brain-to-body ratio of any fish and can even pass the mirror test for self-recognition. Individual rays in local populations are catalogued by researchers using their unique belly spot patterns.

Oceanographic Drivers and Kona Context

The Big Island's volcanic structure plays a critical role in local manta behavior. Deep, nutrient-rich currents are pushed upward along the steep underwater slopes of the island's volcanoes—a phenomenon known as upwelling—creating a year-round plankton supply. Because this food source is continuous, Kona's Hawaiian reef mantas form a resident, non-migratory population, unlike migratory species such as whales.

While other global destinations like the Maldives, the Great Barrier Reef, or the Galápagos feature cleaning stations where mantas gather to be groomed, Kona's sites serve as active feeding stations. Here, mantas engage in dynamic barrel-rolling to gather concentrated plankton. Powerful submerged lights at night act like a dinner bell, gathering plankton in a predictable location.

Protecting Mantas Through Tourism

Sustainable marine viewing offers a viable alternative to consumptive trade. The Big Island's Kona coast features the only reliable year-round manta night snorkel in Hawaii, where filter-feeding mantas are attracted to lit platforms at night. Visitors can observe these resident filter feeders in their natural habitat by booking a manta night snorkel or reviewing options for Kona manta tours.

FAQ

Why are manta rays hunted for their gill plates?

Manta rays are targeted for their gill plates, which are dried and sold for use in unregulated traditional remedies, despite a complete lack of accepted clinical evidence supporting those health claims.

How are international manta product sales regulated?

International trade in manta ray products is regulated under CITES Appendix II, which mandates permits for international trade to prevent illegal or unmonitored commercial transactions.

What makes Kona's manta ray population unique?

Thanks to volcanic island-mass upwelling that creates a continuous plankton supply, Kona hosts a resident, non-migratory reef manta population (Mobula alfredi) that actively feeds at night rather than visiting cleaning stations.

Is a living manta ray worth more than a harvested one?

Yes, peer-reviewed manta tourism valuation studies show that a living manta at a well-managed viewing site generates significantly more long-term local income over its lifespan than a single catch.