Dive 07: "Whaley" Seamount
May 7, 2017
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Dive 07: Hatchetfish

This hatchetfish was imaged during Dive 07 to explore "Whaley Seamount" within the Jarvis Unit of the Pacific Remote Islands Marine National Monument. In order to be nearly invisible in the water column, hatchetfish are highly reflective, have slim profile to limit their shadows, and have photophores on their bellies to mimic downwelling light. Video courtesy of the NOAA Office of Ocean Exploration and Research, Mountains in the Deep: Exploring the Central Pacific Basin. Download (mp4, 25.3 MB)

Dive 07 was conducted on "Whaley" seamount, which rises about 3,700 meters (~12,140 feet) above the seafloor – over 20 times as high as the Seattle Space Needle – and has several small cones protruding from an otherwise flat summit. On this dive, remotely operated vehicle Deep Discoverer climbed the most prominent of these cones – traversing from a depth of 1,100 meters (3,610 feet) to its peak near 800 meters (2,625 feet) of depth.

When we reached bottom, we were immediately greeted by a cusk eel and, moments later, a hermit crab that had chosen to take up residence in a long conical shell. The bottom was composed mostly of loose sediment with ferro-manganese (Fe-Mn) rocks and boulders. Most of the biology was found on rock outcrops. Batfish, though typically a rare observation, were quite common at this site. We documented many corals, including gorgian (plexurids) sea fans; several Anthomastus corals – sometimes referred to as mushroom coral; bamboo corals; cup corals; black corals; and even a nephtheid soft coral. Other biological highlights included glass sponges, anemones, crinoids, gastropods, urchins, brittle stars, sea stars, holothurians (sea cucumbers), a burly-armed squat lobster, carrier crabs, shrimp, oreo dories, hatchetfish, a goosefish, and a Pacific sleeper shark.

We also saw some interesting animals in the water column, including more pelagothurians (pelagic sea cucumbers), jellyfish, and a snake mackerel that followed us when we began the dive.