How Do American and European Eels Migrate to the Sargasso Sea?

Given the paucity of observations on the spawning migration of American and European eels,  a numerical modelling approach is used to explore the movement of eels from the coast to the Sargasso Sea. The positions of “virtual” eels are calculated using a newly developed particle tracking program that includes background ocean currents and various migratory behaviors. Ocean currents are simulated using a realistic model of the North Atlantic (NEMO, 1/4° resolution). The eel is tracked in a quasi three dimensional fashion to include diel vertical migration and energy expenditure calculation. Sensing the Earth’s magnetic field is parameterized in two ways: true navigation and compass orientation. Three migratory behaviors are examined: passive drift, true navigation and compass orientation. The above behaviors are ranked according to (i) the probability of arriving at a spawning area, and (ii) energy expenditure. The ranked assessments show oriented migratory behavior is needed for both American and European eels to reach the Sargasso Sea although it is argued that the energy expenditure is not a critical limiting factor. The top-ranked behaviors and associated migratory path are discussed. The particle tracking program could be a useful tool that can complement ongoing field tracking experiments.