A tagging and release study was conducted last 31 September 2005 in the Kalmar Sound, between Öland and the Swedish mainland, and the following were observed: swimming activity was between dusk and dawn, starting at a light level corresponding to civic twilight and ending in the morning with generally the same light level; during daylight, the eels rested on the seabed at depths of 2-36 m; swimming depth was typically close to the surface, up to 95% of swimming time was spent within 0.5 m of the surface; short dives at irregular

intervals (some 12 per hour) were made down to the thermocline depth, or occasionally, to the seabed, duration of such dives were typically 5-10 min. Although only a few days at liberty, the eels had migrated a considerable distance between recapture and release sites, indicating a mean rate of travel of approximately 16 km per day. The recapture positions suggested unidirectional movements towards the southwestern Baltic Sea, that is, close to the straits leading to the ocean, suggesting that the recorded movements were related to the eel's spawning migratory behaviour (Ref. 81781).

Status of threat: critically endangered (CR) (Ref. 83294).