By Dr. Becker
A number of staggering migration feats are known to science. Gray whales, which hold the record for the world’s longest migration, may log in up to 13,988 miles in 172 days.1
The tiny blackpoll warbler, which migrates from Vermont and Canada to South America, recently broke the record for longest non-stop overwater flight; they may fly for up to three days without stops, over a distance of more than 1,700 miles.2
Monarch butterflies may also travel up to an impressive 100 miles a day during migration. Even mule deer make a 150-mile, often harrowing, migratory trek. Now it turns out an under-appreciated species, the American eel, can be added to the list of creatures making lengthy and impressive migrations.
Eels May Migrate Nearly 1,500 Miles
The oceanic migration of adult American eels has remained a mystery, researchers from Dalhousie University noted, until now. The eels have been sighted in North American inland rivers while their larvae have been detected in the Sargasso Sea, which is near Bermuda.
But no eel had ever been observed traveling across the open ocean to reach the theorized spawning area — until now. Researchers attached satellite-transmitting tags to 38 eels collected from Nova Scotia, Canada, then tracked their movements after they were released.
Previous attempts have seen the tags fall off prematurely or be consumed by predators, but in this case eight of the eels traveled through the open ocean, with their tags still attached.
The eels were recorded swimming at a depth of 1.2 miles, and one eel, which the researchers named “Star,” swam all the way to the Sargasso Sea — a nearly 1,500-mile journey — before the tag was lost.
Study co-author Martin Castonguay, Ph.D. of Fisheries and Oceans Canada told Discovery News the eels’ migration represents “one of the longest and most amazing migrations in the animal kingdom.”3 According to the study, which was published in Nature Communications:4
“The reconstructed routes suggest a migration in two phases: one over the continental shelf and along its edge in shallow waters; the second in deeper waters straight south towards the spawning area.
This study is the first direct evidence of adult Anguilla migrating to the Sargasso Sea and represents an important step forward in the understanding of routes and migratory cues.”
Eels Face a Difficult Journey
The eels’ migration is not for the faint of heart. As they swim out of the inland rivers, some eels must pass through hydropower dams and may be killed by turbines. Other eels may be eaten by sharks and tunas as they try to swim out to sea.
While in the open ocean, the eels burn their stored fat for energy, not stopping to eat. It’s thought they travel at deeper levels during the day to avoid predators, as well as swim in cooler waters to conserve energy.
Castonguay described the Sargasso Sea as an “eel mecca,” noting that more than 30 species of eels spawn there. However, only the American eel and the European eel travel back to continental waters to grow.5
As American eels are classified as an endangered species and are included on the International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species, the migration discovery may pave the way for protections to help the eels migrate safely.
The researchers have planned another round of studies, using improved tag attachment, that they hope will shed even more light on the eels’ spectacular journey.
Insight Into the Life of the American Eel
American eels spend most of their lives in freshwater habitats in the Great Lakes or in estuaries (the waterways between rivers and the open sea). “They can live to be twenty years or more before returning to the open ocean to spawn. But it is their final act — the animals die soon after,” according to National Geographic.6
It’s thought that young eels are carried to the Atlantic shore of the eastern U.S. via the gulfstream, and they eventually swim up rivers. The building of dams has impeded some of their routes, causing numbers far inland to plummet.
As certain dams are torn down, numbers increase. For instance, two years after the Embrey Dam on the Rappahannock River in Virginia was taken down, researchers measured a significant increase in the number of eels.7 Some areas have also employed mechanism to restore eel passage around dams.
Eels were once a valuable food source for Native Americans, although they’ve never really caught on among modern fishermen because of their snake-like appearance, at least in the U.S. In Europe and Asia, eels play a major role in the human diet.
The American eel is the only freshwater eel in North America. It faces threats from hydroelectric facilities and dams, but the U.S. Fish and Wildlife Service (FWS), which reviewed their status in 2015, has found that Endangered Species Act protection is not needed at this time. According to the FWS:8
“American eels remain widely distributed throughout much of their historical range, despite reduced numbers over the past century and habitat loss from dams and other obstructions. In some coastal rivers, eels are the most commonly found fish, occupying more aquatic habitats than any other species.”