First Phase Of Danish Eel Expedition Completed

Denmark’s largest marine research vessel has spent three weeks exploring and gathering samples in the spawning grounds of the European eel in the Sargasso Sea, making at least two stops in Bermuda during their time.

The first phase of the Danish Eel Expedition has been successfully completed, with the expedition comprising experts from a number of Danish and international universities. A total of 20 researchers and 17 crew members participated in the first leg of the exhibition.

The team was investigating whether climate-related changes to the eel spawning grounds or the ocean currents that carry the eel larvae to Europe have caused the dramatic decline in eel numbers.

Slideshow of the vessel Dana docked in St. George’s last month:

The research institute said, “The first leg of the expedition investigated conditions in the eels’ central spawning areas in the Sargasso Sea at 41 carefully chosen locations where cold and warm waters meet, as this is believed to create good conditions for eel larvae.

“As something unique, the expedition was able to perform a comprehensive ’24-hour vertical study’ of a hotspot with a particularly high concentration of eel larvae.

“The study showed that by far the most eel larvae were collected over a 24-hour period in a small band at a depth of 150 metres, just below where the water has the highest salt level. For 24 hours, the expedition performed measurements on organisms and the environment around the larvae to work out what makes that specific location so attractive to the larvae.

“The expedition mapped the distribution of marine snow [organic detritus] and jelly plankton [primarily medusa jellyfish] at various depths in the nursery grounds of the eel larvae. Marine snow and jelly plankton such as appendicularians are likely candidates as an eel larvae food source.

“No one has yet succeeded in catching a mature European eel in the Sargasso Sea. The expedition therefore trawled for three nights around the new moon—when it is assumed eels spawn, so the eggs have the best chance of being concealed in the dark from hungry predatory fish. However, no adult eels were caught this time either, although many smaller fish, particularly deep sea fish, were caught.

“During the first leg of the expedition, over 400 eel larvae were retained for further on-shore DNA analysis. This might reveal whether there are genetic differences in the populations, and whether the two species which spawn in the Sargasso Sea—the American and European eel—interbreed.”

The Sargasso Sea, a vast patch of ocean named for a type of free-floating seaweed called Sargassum, is home to many endemic species, with over 150 invertebrate species living on, or in association with, the Sargassum. Bermuda is the only land mass in the Sargasso Sea.

Last month, representatives from the governments of 11 countries and territories from around the Sargasso Sea and Europe met to reaffirm their support for an initiative, led by Bermuda, to collaborate for the conservation of the Sargasso Sea.

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Category: All, Environment