Mariana butterflyfish
APRA, Guam — Last month, during Ocean Exploration Trust’s exploration of Ahyi Seamount (a shallow submarine volcano in the Commonwealth of the Northern Mariana Islands), the Corps of Exploration aboard exploration vessel Nautilus dove remotely operated vehicle Hercules and found a stunning display of biodiversity. One of the most exciting animals spotted along the slope was a school of yellow-crowned butterflyfish (Chaetodon flavocoronatus). C. flavocoronatus (flavo = yellow, coronatus = crown) is a deep-water fish endemic to the Mariana Islands but rarely caught on video.
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Chaetodon flavocoronatus is part of the poorly known group of Indo-West Pacific butterflyfish. The species was discovered and named in the early 1980s by Robert Myers at the University of Guam Marine Laboratory. That original sample was obtained at a depth of 36 meters, while Nautilus’ video was recorded around 94 meters deep. According to biologist Brent Tibbatts, this depth s is near the maximum depth this species has been recorded from, and the Ahyi Seamount is near the northernmost sighting of this species.
“This butterflyfish was first found and described from Guam in the 1980s. Sightings of this species are rare, and until recently, limited to the Mariana islands. An individual was seen in the northern Philippines, and one in the Ogasawara islands, around 1600km northwest of Guam, but all other sightings are limited to the Mariana Islands, so it is virtually endemic to our island chain,” says Brent Tibbatts, fisheries biologist, Guam Department of Agriculture Division of Aquatic and Wildlife Resources. “Sightings of a group this size are unprecedented…very exciting to see this many in one place.”
Ahyi Seamount summits 61 meters below the ocean surface, between Maug and Farallon de Pajaros in the Northern Mariana Islands, within the Volcanic Unit of the Mariana Trench Marine National Monument. Our dive site on the seamount intersected with depths suitable for bottomfish habitat, which are priorities for resource management in the region. During the dive, we also recorded live videos of moray eels, sea urchins, and a variety of other shallow water biodiversity.
This dive was part of the Mattingan: Mariana Arc Volcanic Exploration expedition to explore deep-sea areas identified by the local management and science community, including sites with signatures of active volcanism, abyssal plain habitats, and areas in and around the Monument. Collected data will support resource management priorities. This expedition was supported by NOAA Ocean Exploration, the Bureau of Ocean Energy Management, and the U.S. Geological Survey via the Ocean Exploration Cooperative Institute.
“Thanks to our telepresence technology, OET is proud to share these beautiful, bright yellow fish with the people of the Mariana Islands and the entire world,” says Jamie Zaccaria, Outreach and Media Coordinator with OET. “This is a wonderful reminder of the vastness of what remains to be seen and discovered in our global ocean.”
All of OET’s ocean exploration is streamed live on NautilusLive.org, a 24-hour platform that brings ocean exploration directly to viewers on shore. Telepresence technology allows viewers to engage with the team at sea, asking questions and receiving real-time behind-the-scenes updates via social media. Classrooms worldwide are invited to connect with the at-sea team via free educational Q&A interactions.
The OET 2025 field season will continue with exploration of Solomon Islands, the Republic of the Marshall Islands, and Wake Atoll. OET’s 2025 expeditions will build ocean knowledge supporting international scientific and U.S. governmental priorities, particularly understanding the deep sea, sharing that knowledge with others, and contributing new discoveries and data to inform future resource management decisions. Through the open sharing of data collected during these expeditions, OET directly contributes to the US National Strategy for Ocean Mapping, Exploration, and Characterization, the Beyond the Blue: Illuminating the Pacific campaign, and other coordinated initiatives.
About the Ocean Exploration Trust
The Ocean Exploration Trust was founded in 2007 by Dr. Robert Ballard to explore the ocean, seeking out multi-disciplinary discoveries while pushing the boundaries of STEAM education and technological innovation. Its international program is launched from aboard the Exploration Vessel Nautilus, offering live exploration to participants on shore and the public via live video, audio, and data feeds.
The 2025 E/V Nautilus expeditions are sponsored by NOAA Ocean Exploration via the Ocean Exploration Cooperative Institute, including additional support from the Bureau of Ocean Energy Management, in collaboration with the US Geological Survey. OET program sponsors and partners for 2025 also include the Office of Naval Research, QPS, and the Phillip Stephenson Foundation.
