Using a Coupled Bio-Physical Particle Tracking Model to Improve Our Understanding of Eel Behaviour during the Early Phase of the Marine Migration

The American eel is a facultative catadromous fish inhabiting continental waters but migrating long distance for spawning in the Sargasso Sea. Despite its status of major concern in Canada, its migration pattern from rivers to the open ocean is poorly documented. Recent field tracking (acoustic and satellite) provided the first data about the migratory pattern of silver eels from the fresh to marine waters of the St. Lawrence system (Canada). These data were used to develop a particle-tracking model which incorporates directed swimming motion. Thousands of particles with various horizontal and vertical behaviours were tracked from the St. Lawrence Estuary to the exit of the Gulf (distance of ca. 800 km). Their effectiveness was compared using the observed data of eels acoustically detected within the Gulf and at its exit during recent field experiments. This modeling approach showed that at least two combined active behaviours (nighttime selective tidal stream transport and an internal compass) are necessary for eels to move out the Gulf within the observed time window.