News
Giant manta rays found to be predators of the deep ocean
A new scientific study by the Marine Megafauna Foundation (MMF), the University of Queensland (UQ) and Proyecto Mantas Ecuador has been published in Royal Society Open Science today, providing novel insights into the food sources of giant manta rays found in the eastern equatorial Pacific.
The giant manta ray (Manta birostris) is a filter-feeding and highly migratory marine species found in tropical and temperate waters worldwide. The large majority of existing information about the species’ diet is based on observational data limited to feeding activities at the sea surface during daylight at well-known aggregation sites.
This new study focused on Isla de la Plata, an island off Ecuador, which seasonally hosts the largest known aggregation of giant manta rays in the world. Manta ray muscle and surface zooplankton were examined through stable isotope analysis, and revealed that the species’ dietary intake largely comes from the mesopelagic zone (200 to 1,000 meters below the ocean surface) rather than from surface zooplankton as previously thought.
MMF’s manta ray researcher Katherine Burgess, who authored this study as part of her PhD project at the University of Queensland, commented: “Manta rays are one of the most iconic marine animals, yet we still know very little about their feeding habits. The study reports much-needed information on the diet of this elusive species.”
Katherine Burgess taking a tissue sample of a giant manta ray in Ecuador. Copyright: Andrea Marshall
“We studied the giant manta rays’ diet using biochemical tests, such as stable isotope analysis, which work on the ‘you are what you eat’ paradigm. These tests can determine what animals have been eating by examining a piece of tissue from a muscle biopsy from a free-swimming animal,” she added.
Professor Anthony Richardson, a scientist with UQ’s School of Mathematics and Physics and the CSIRO’s Oceans and Atmosphere Flagship, said: “The research found an average 27 per cent of the giant manta rays’ diet comes from surface zooplankton and 73 per cent from mesopelagic sources including fish from 200m to 1,000m below the ocean surface.”
“The deep ocean is the next frontier for open ocean fisheries, and we are only just realizing the potential reliance on this zone by threatened marine megafauna,” he added.
Giant mantas are known to dive to depths of over 1,000 meters making it difficult to study their feeding ecology. To determine the diet of a fish, researchers normally examine its stomach contents. However, this is usually a distressing or lethal procedure and would not be appropriate considering global manta ray populations have been in drastic decline due to anthropogenic threats such as targeted fishing or bycatch, pollution and habitat destruction.
Both species of Manta – the giant manta ray (Manta birostris) and reef manta ray (Manta alfredi) – are listed as ‘vulnerable to extinction’ on the IUCN Red List of Threatened Species. To date, manta rays are formally protected in Ecuador, Peru, New Zealand, the USA (Florida, Hawaii and Flower Garden Banks), Guam, Maldives, Yap, Indonesia, the Philippines and Mexico only. Filling the knowledge gaps on manta ray feeding ecology is crucial for the identification of critical habitats and aggregation sites, which are vital for developing effective conservation measures for these species.
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Renowned anti-whaling activist Paul Watson has been released from custody in Greenland after spending five months in detention. Denmark’s Justice Ministry rejected Japan’s request for his extradition, citing insufficient guarantees that his time already served in custody would be credited against any potential sentence.
The 74-year-old Canadian-American was arrested on July 21 in Nuuk, Greenland’s capital, when his ship docked to refuel. His arrest was based on a 2012 Japanese warrant related to a 2010 encounter in Antarctic waters. Japan alleged Watson obstructed operations and caused damage to a whaling research ship during efforts to disrupt illegal whaling. Watson has consistently denied these claims, maintaining his commitment to marine conservation.
Denmark, which oversees extradition matters for Greenland, concluded that while the legal conditions for extradition were met, the lack of assurances from Japan regarding time-served credit made extradition untenable.
In a video shared by his foundation, Watson expressed gratitude and relief, saying, “After five months, it’s good to be out… and good to know they’re not sending me to Japan.” He added that the most difficult part of his time in custody was being separated from his two young sons.
Watson is a pioneering figure in marine conservation, known for founding the Captain Paul Watson Foundation in 2022 after decades of activism with the Sea Shepherd Conservation Society. His bold efforts to defend marine life have earned him widespread support, including from celebrities and conservationists. His work has also been featured in the acclaimed reality TV series Whale Wars.
Watson’s lawyer, Jonas Christoffersen, praised the decision, stating, “We are happy and relieved that Paul Watson is now free.” He added that Watson is eager to reunite with his family and continue his vital work.
The arrest occurred while Watson’s vessel, the M/Y John Paul DeJoria, was en route to the North Pacific with a team of 26 volunteers to intercept a Japanese whaling ship. His foundation described the arrest as politically motivated and emphasized that Watson’s actions were focused on ending illegal whaling practices.
Japan resumed commercial whaling in 2019 after leaving the International Whaling Commission, asserting that whale meat is a cultural tradition. Conservationists, however, continue to challenge these practices, highlighting their impact on marine ecosystems.
Despite the challenges, Watson remains steadfast in his mission to protect marine life and bring attention to whaling practices. His dedication to ocean conservation has made him a globally respected advocate for the environment.
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