Natures wonders: eel migration to sargasso sea (Introduction)

by David Turell , Wednesday, October 19, 2022, 02:06 (556 days ago) @ David Turell

A long trip via the Azores:

https://www.sciencealert.com/scientists-track-eels-to-their-ocean-breeding-grounds-in-w...

"After generations of speculation, scientists have finally managed to track European eels the entire way back to their breeding grounds in the Sargasso Sea – following their movements thousands of kilometers along what is considered one of the most impressive animal migrations in nature.

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"European eels migrate between 5,000 and 10,000 kilometers (3,100 to 6,210 miles) to spawn at sea, after which their larvae drift back towards land and the relative safety of rivers.

"Using satellite tags, the researchers behind this latest discovery obtained tracking data from 21 female European eels as they navigated the last leg of their epic journey, southwest from the Azores, a volcanic archipelago in the North Atlantic Ocean, far west of Portugal.

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"Past research tracking eel migrations had shown eels from all over Europe converge around the Azores islands before departing for the Sargasso Sea, an ocean region bounded by four swirling ocean currents and named for its vast forests of Sargassum seaweed.

"The eels were captured, tagged with detachable satellite trackers, swabbed for DNA testing, and released back into the Atlantic Ocean from the Azores islands back in 2018 and 2019.

"Six eels reached the Sargasso breeding grounds months later with their satellite trackers still attached; data from 15 other eels were collected along the way. The longest recorded straight-line distance was 2,275 kilometers (1,410 miles).

"'Their journey will reveal information about eel migration that has never been known before," says fisheries biologist Ros Wright of the UK Environment Agency, who led the study.

"It's still unclear how the eels find their way to the Sargasso Sea or even how long their spawning season extends.

"The swimming speed of the eels in this study, which averaged 6.8 kilometers (4.2 miles) a day, and the length of their marathon journey – which takes more than a year – suggests these long-haulers need to make a very calculated migration.

"'Rather than make a rapid migration to spawn at the earliest opportunity, European eels may instead make a long, slow spawning migration at depth that conserves their energy and reduces mortality risk," Wright and team write in their published paper.

"'This timing would enable the completion of their reproductive maturation before they arrive at the spawning area."

"'It's also incredible to know they go way deeper than 1,000 meters on the way!" James Maclaine, a senior fish curator at the UK National History Museum, tweeted. That's plunging more than 3,280 feet down into darkness.

"But questions remain over the eels' timing and navigation across thousands of kilometers in open ocean to reach the Sargasso Sea.

"It could be that they sense Earth's magnetic fields like Chinook salmon (Oncorhynchus tshawytscha), which return to the exact stream where they hatched. Sniffing out olfactory cues or following ocean currents or temperature fronts are other possibilities, too."

Comment: this circuitous route suggests dhw's fairy tale of brave ones wandering off in hope of finding warmth fits this meandering migration. It fits in an unprepared way in just blundering around and searching. Using the Earth's magnetic field has been previously established. Witch tells them just swim south and wa' la' the Azores are right in the way.