Migration Secrets of the European Eel Partially Revealed

The European eel undertakes one of the longest known spawning migrations in the marine environment, completing a non-stop 5,000-kilometre journey from Europe to its spawning grounds in the Sargasso Sea, south of Bermuda off the coast of the Bahamas. The migratory movements of adult eels in the coastal waters of the continental shelf have been documented, but until quite recently, scientists knew little about the high seas portion of their journey. In 2006, research scientist Martin Castonguay from the Maurice Lamontagne Institute in Mont-Joli, Québec, helped unlock a few of the mysteries surrounding this journey. It is now known that eels make significant daily vertical migrations during their oceanic migration.

At the invitation of Danish colleagues, Dr. Castonguay joined a research mission aimed at following and describing the migration of adult European eels from the continent to their spawning grounds. This mission differed from previous studies in that it employed satellite tracking technology not previously used on this species. The team attached satellite tags to the backs of the eels in order to collect data on their movements. Because of the large size (approximately 20 cm) of the satellite tracking device relative to the size of the eels, the tags were fitted on the largest specimens (more than 80 cm). Approximately 20 adult females thus left Europe, fitted with tags. Unfortunately, since the attachment methods were poorly adapted to medium-size species such as eel, the devices detached prematurely.  However, the data collected during the first 1,300 kilometres provided some interesting insights. For instance, the biologists discovered that the eels make daily vertical migrations, from a depth of 600 metres during the day to 200 metres at night. The researchers believe that this behaviour may be a thermoregulatory mechanism to control gonad development or a predator avoidance strategy.

Further research is therefore needed to learn more about the European eel’s odyssey. However, the innovative nature of the mission and the data collected earned the researchers the privilege of publishing the results of this first phase in the prestigious journal Science in 2009 (Oceanic Spawning Migration of the European Eel (Anguilla anguilla)

The eel has a very unusual life cycle. It is a catadromous species, i.e., it spawns in saltwater in the ocean, but spends most of its life in freshwater rivers. After 15 to 20 years living in freshwater, the eels reach sexual maturity and migrate to the Sargasso Sea to spawn. Eels spawn only once in their lifetime and after spawning, the adult eels die. The spawning migration documented by Dr. Castonguay and his colleagues corresponds to the eels’ return to their birthplace and represents the last stage of their life: a six-month crossing, without feeding, to reach their spawning sites and complete their life cycle. The larvae that hatch on this side of the ocean are carried to Europe on the Gulf Stream. It will take them two years to reach the European coast, where they will swim in the rivers in which their parents lived.

Figure 1 - European eel. Photo FishBase/Steffen Zienert