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University of Hawaii
The largest aggregation of fish ever recorded in the abyssal deep sea was discovered by a team of oceanographers from the University of Hawaii in Mānoa, Monterey Bay Aquarium Research Institute and National Oceanography Center (NOC). The results were published in Deep-Sea Research.
“Our observations really surprised us,” said Astrid Leitner, lead author of the study, who led this work as a graduate researcher at UH Mānoa’s School of Ocean and Earth Science and Technology (SOEST). “We have never seen reports of such a large number of fish in the sparsely populated deep sea with limited food.”
Effect of seamounts on deep sea biology
The researchers, including Leitner, Jennifer Durden of the NOC and UH Mānoa professors Jeffrey Drazen and Craig Smith, carried out the observation during an expedition to the Clarion Clipperton (CCZ) area. The CCZ is a vast region extending almost from Hawaii in Mexico, which is being explored for deep-sea extraction of nodules containing metals such as copper, cobalt, zinc and manganese.
Abyssal submarine mountains, deep submarine mountains whose peaks lie 3,000m below the sea surface, dot the deep seascape and are some of the least explored habitats on the planet. During the expedition, the research team took samples from three of these seamounts and the surrounding lowlands as part of an effort to establish an ecological baseline prior to mining activities.
On top of one of three previously unmapped and completely unexplored seamounts, the team captured on video a swarm of 115 merciless eels (Synaphobranchidae family) in a small bait package containing about 2 pounds (1 kg) of mackerel. Some eels have been caught in a bait trap and identified as Ilyophis arx, a little-known species with fewer than 10 specimens in fish collections around the world.
These eels have been observed on top of all seamounts, but not on the surrounding abyssal plain. The findings provide evidence for an effect of abyssal seamounts (where these mountains can support a much higher number of animals than other surrounding habitats) and also indicate that these eels are likely seamount specialists.
Upon returning from the expedition, the team determined they had documented the largest number of fish ever recorded in the abyssal ocean at one time, nearly double the previous record.
For more information, see the SOEST website.
—From Marcie Grabowski
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