Massive Basketwork Eel Aggregation Discovered at Patience Seamount

A year-round deep-sea aggregation of more than 2.8 million basketwork eels has been quantified on Patience Seamount. The discovery, based on nine acoustic surveys conducted between 2023 and 2025, reveals a major reproductive hotspot in the Huon Marine Park.

The aggregation is not a fleeting event. It persists throughout much of the year, with documented presence from December to August. Numbers and biomass peak sharply during the southern autumn months from March to May. The swarm of eels forms a vast cloud extending roughly 3 kilometers long, 2 kilometers wide, and 150 meters above the seafloor.

The sheer biomass of the gathering is staggering. It increased from around 750 metric tons in March to more than 3,500 metric tons by May, with a peak recorded biomass of 3,550 metric tons.

Reproductive behavior confirmed

The primary reason for this massive gathering is spawning. Scientific examination confirmed that females within the aggregation were carrying eggs at an advanced stage of development. Their empty stomachs further indicated a physiological shift away from feeding and toward reproduction.

This reproductive behavior explains the seasonal surge in numbers. The eels converge on the seamount specifically to breed, creating one of the largest known deep-sea spawning aggregations.

Ecological context and recovery

The phenomenon is occurring within a marine protected area showing signs of ecological recovery. Patience Seamount sits inside the Huon Marine Park, which was established in 2007 as an expansion of a 1999 marine reserve.

The area was previously damaged by bottom trawling. That activity has now ceased. Researchers note rebuilding populations of orange roughy and the return of corals to previously trawled areas. The seamount now hosts a complex ecological community.

While orange roughy gather on the steeper upper slopes, the basketwork eels dominate the deeper, flatter terrain around the seamount's base. Their year-round presence and intense seasonal spawning activity underscore the site's regained ecological significance. Ben Scoulding, a researcher involved in the study, highlighted the integrated methods required for such work. "Even with calibrated multi-frequency acoustics, camera imagery and physical sampling remain essential for species identification, size estimation and bioinformatics analysis," he said.

The research detailing this discovery was published in the journal Royal Society Open Science. The aggregation's persistent presence acts as a living indicator of the recovering health of the Huon Marine Park ecosystem.