Silver eel migration behaviour in the Baltic

Abstract

Westerberg, H., Lagenfelt, I., and Svedäng, H. 2007. Silver eel migration behaviour in the Baltic. – ICES Journal of Marine Science, 64: 1457–1462 Female silver eels (Anguilla anguilla L.) were tagged with data storage tags and released in the Baltic Sea at the same time at a single site on the east coast of Sweden. Data on temperature, light, and depth were obtained from six eels, continuous records for 71 d at sea. The swimming behaviour was similar for all fish, almost stereotyped: swimming activity was between dusk and dawn, starting at a light level corresponding to civic twilight and ending in the morning at 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 1–2 h−1) were made down to the thermocline depth, or occasionally, to the seabed. The 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 ∼16 km d−1. The recapture positions suggested unidirectional movements towards the southwestern Baltic Sea, i.e. close to the straits leading to the ocean, supporting a belief that the recorded movements were related to eel spawning migratory behaviour.

Vertical migrations may control maturation in migrating female Anguilla dieffenbachii

“…Tesch 1978, 1989, 1995, Tesch et al 1991, Jellyman & Tsukamoto 2002, Westerberg et al 2007, Aarestrup et al 2009, with daytime diving and nighttime ascents, sometimes to the surface (Sasai et al 2001, Westerberg et al 2007. In shallow or continental waters, multiple dives have been observed within a single night (Tesch et al 1991, Westerberg et al 2007), but a single descent/ascent pattern becomes established in oceanic water (Tesch 1978, Jellyman & Tsukamoto 2002, Aarestrup et al 2009. Typically, ascents do not bring eels close enough to the surface for celestial navigation cues (Tesch 1989, Jellyman & Tsukamoto 2005, and geomagnetism is thought to be the more likely means of navigation (Tesch et al 1992, Moore & Riley 2009).…”

“…The alignment of popup locations of the tags in the present study suggests that the eels were using a similar migration route. The use of similar routes is likely within enclosed waterways like the Baltic Sea (Westerberg et al 2007), but relatively few silver eels have been caught in the open ocean (Todd 1973, Sasai et al 2001, Chow et al 2009). As silver eels are known to use magnetic orientation at sea (e.g.…”

Behaviour of stocked and naturally recruited European eels during migration

“…Longitude was calculated by using the diurnal swimming depth changes of the eel as a proxy for sunset and sunrise; this provides an estimate of the time of local noon and thereby the longitude (Nielsen et al 2006). All the eels displayed this diurnal cycle, and there is strong justification to believe that the depth changes are cued to dawn and dusk (Westerberg et al 2007). Fig.…”

“…1100/2007. This regulation requires the member states to prepare eel management plans (EMPs) for all eel habitats.…”

Ecosystem Services Linking Social and Ecological Systems: River Brownification and the Response of Downstream Stakeholders

“…It is reasonable to assume that the character of the sea water, as perceived by eel, changes in strokes of water from Helge River. As migrating eel in the Baltic typically swim close to the surface, more than 90% of the time less than one meter deep, they would come across the brownish river water when entering the estuary of River Helge å (Westerberg et al 2007) because river water will float on top of the more dense sea water. This may cause eel to actively avoid the brownish water or seek out water with other qualities.…”