In fact, the eel recruitment in the model fluctuated significantly, mimicking the patterns reported across Europe. "In the early 1980s, for example, only a fraction of the larvae managed their way to Europe," reports Professor Biastoch. The researchers found that small-scale, wind-driven ocean currents strongly determine the eel population fluctuation. Depending on the presence of regional currents in the Sargasso Sea, the larvae's path to Europe was either extended and led to low recruitment or shortened leading to high recruitment in Europe. "We had not seen these flow changes in any of the older ocean models. But they seem to play a crucial role in the migration of the eel larvae," explains Professor Biastoch.
Combining those discoveries with genetic analyses, the scientists found evidence that, contrary to what is typically thought, eels do not return to random locations in the Sargasso Sea to reproduce but rather return to where their mother spawned in particular locations within the Sargasso Sea. "This is a new finding - so far, it was assumed that the mating in the Atlantic takes place completely independent of the area of origin and future scientific expeditions will have to verify this result in situ " says Baltazar-Soares.
The ultimate fate of eels making the long migration from the Sargasso Sea to the continental waters of Europe is still very difficult to predict, even using state of the art techniques. Indeed, from the 1960s to the 1980s, the results of the computer simulation matched up well with the observed occurrence of young eels reaching the European coasts. After that, however, the status of eel populations seems to be disconnected from the clima
|Contact: Jan Steffen|
Helmholtz Centre for Ocean Research Kiel (GEOMAR)