Scientists estimate up to 2.8 million eels gather at Tasmania seamount
Surveys at Patience Seamount put a number on an annual gathering of basketwork eels, while leaving the reason they choose that site unresolved.
Researchers led by Australia's CSIRO estimate that as many as 2.8 million basketwork eels gather at Patience Seamount in the Huon Marine Park off Tasmania. The study, published on October 28 in Royal Society Open Science, puts a number on an annual deep-sea gathering that had not previously been quantified and offers evidence that the eels assemble to reproduce.
Marine scientist Ben Scoulding led the team, which estimated the eels' combined mass at about 3,550 metric tons. The figure is an estimate of the aggregation's possible size, rather than a count of every animal, according to Phys.org's account of the study.
How researchers estimated the eel gathering
The researchers carried out nine acoustic surveys between 2023 and 2025, sending sound waves into the water to measure echoes from groups of fish. They also towed underwater cameras behind a research vessel and collected a small number of eels. Combining those observations and samples with the acoustic readings allowed the team to estimate both the number of eels and their total weight.
That combination mattered because orange roughy also gather at Patience Seamount. Sonar can measure the density of a fish aggregation but cannot reliably tell the two species apart on its own. The study team said camera images and physical samples remained essential for identifying species and estimating their size.
The eels, known scientifically as Diastobranchus capensis, form dense swarms at a particular depth along the mountain's western side instead of spreading across it. Metro reported that the annual gathering peaks from March to May and disperses in October, giving researchers a recurring event to observe rather than a single encounter.
Why the eels may gather at Patience Seamount
Most female eels examined had eggs at an advanced stage of development, and all the sampled eels had empty stomachs, Phys.org reported. The researchers interpreted those findings as support for spawning rather than feeding as the reason for the gathering. They have not established why the eels choose Patience Seamount: among about 120 underwater mountains in the area, they recorded no comparable mass gathering elsewhere.
Molly Fowkes, an eel researcher at Lancaster University, told Metro that the gathering might resemble the long-distance migrations of European eels to presumed spawning grounds in the Sargasso Sea. She presented that as a possible comparison, while saying the cues that draw basketwork eels to this particular mountain and coordinate their behaviour remain unclear.
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Sources and context
- Scientists count more than 2 million eels on one underwater mountainPhys.org (Paul Arnold; original report)
- A giant ball of 2,800,000 eels is having an orgy off the coast of AustraliaMetro (Ryan Prosser; original report)
AI-assisted article checked against the listed sources. NewsJaws did not conduct interviews or attend the reported events.