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Gathering of 2.8 Million Eels Around Patience Seamount
Policy2 min read
Scientists counted how many basketwork eels gather each year around Patience Seamount, an underwater mountain off southern Tasmania, Australia. At the peak, about 2.8 million eels weigh more than 3,500 tonnes.
A huge yearly eel gathering
Every year, millions of basketwork eels gather around an underwater mountain called Patience Seamount to breed. A team led by ocean scientist Ben Scoulding at CSIRO, an Australian science agency, published the first estimate of how large this gathering is. The study appeared on October 28 in the journal Royal Society Open Science.
Key numbers
- At the peak, the gathering can include about 2.8 million eels.
- Their total weight can be more than 3,500 tonnes.
- The eel group at the peak is about 3 km long, 2 km wide and 150 m tall.
- The eel weight grew from about 750 tonnes in March to over 3,500 tonnes in May.
- Patience covers only about 2 km², yet it supports the gathering for months.
How scientists found it
Fishing grounds reported unusual numbers of these eels in the area since at least the 1980s and 1990s. In 2007, CSIRO scientists first filmed the event by towing a camera behind a research ship. Later surveys from 2023 to 2025 used sound waves to map where the eels were. Sound alone could not tell eels apart from orange roughy, another fish that lives there, so the team matched sound data with underwater camera images.
Why it matters
The eels are still a mystery. Scientists do not yet know why Patience attracts so many eels, while nearby underwater mountains with similar depth and conditions do not. The basketwork eel is also listed as a species at risk of extinction, partly because it is often caught by accident. In New Zealand, one eel group on a continental slope fell 85% in 40 years, and it is not known if Patience's eels are falling too.
What to watch
- Scientists are testing ideas, such as how close the mountain is to the continental shelf and how ocean currents move.
- Researchers will need to check whether the Patience eel population is shrinking.
- Future surveys may show whether the gathering changes over time.
Glossary
- Patience Seamount
- An underwater mountain off southern Tasmania where millions of eels gather each year to breed.
- CSIRO
- Australia's national science agency, which does research on many topics, including the ocean.
- basketwork eel
- A deep-sea eel species (Diastobranchus capensis) that gathers in large numbers at Patience.
- sound waves
- Sound sent through water to find and map fish. Scientists use the echoes to estimate how many fish are there.
- orange roughy
- A deep-sea fish that also lives around Patience and can look similar to eels in sound data.
- continental shelf
- The shallow, sloping edge of a continent that runs down into the deep ocean.