Large-scale migration patterns of silver American eels from the St. Lawrence River to the Gulf of St. Lawrence using acoustic telemetry

Abstract

Downstream migration of silver American eels (Anguilla rostrata) from the St. Lawrence system was examined using acoustic telemetry. One hundred and thirty six silver American eels were tagged, and their passage was recorded using fixed acoustic arrays covering a 420 km distance along the St. Lawrence River and Estuary. Eighty-nine percent of the tagged eels were detected. All migrant eels (111) exhibited unidirectional and downstream movements, but the migration was not completed in one continuous direct movement. High individual variability in migratory longitudinal profiles was documented as well as in individual speed with no apparent relation to river discharge or morphological traits. Migration speed increased over the season. Our observations demonstrated that migrating silver American eels are largely nocturnal and demonstrated the use of nocturnal, ebb tide transport to leave the estuary. With 44 additional eels tagged and released in the maritime estuary, escapement of 180 silver American eels from the Gulf of St. Lawrence system was monitored along a 125 km acoustic line that entirely covered Cabot Strait in 2011. Surprisingly, only four of the tagged eels were recorded escaping the Gulf of St. Lawrence.

Freshwater and coastal migration patterns in the silver‐stage eel Anguilla anguilla

“…A possible interpretation of migration patterns shown here, which has been raised by other studies, is that sea migration could be a two‐step migration process (Durif et al , ; Aarestrup et al , ; Béguer‐Pon et al , ; Stein et al , ). It has been reported that A .…”

“…anguilla may exploit outgoing tidal currents while migrating in the transitional and sea‐lough compartments with 92% of migration initiations occurring at these times. This accords with findings by Béguer‐Pon et al () who reported that American silver eels Anguilla rostrata (LeSeuer 1817) use nocturnal ebb‐tide transport to migrate out of the St Lawrence Estuary. The A .…”

Fine‐scale swimming movement and behaviour of female silver eels, Anguilla dieffenbachii, within a lake affected by hydro‐power generation

“…Such speeds and those described above for eels within Lake Manapouri, are within the range of those recorded for female silver eels of other species e.g . Anguilla anguilla L.: 1.08–4.32 km/hr (Behrmann‐Godel & Eckmann, ); 2.02 km/hr, (Bultel et al., ); Anguilla rostrata LeSueur: 0.83 km/hr (Béguer‐Pon et al., ).…”

“…Ancestors of anguillid eels were tropical marine species (Tsukamoto & Aoyama, ), and hence anguillids have retained tropical marine spawning, necessitating extensive migrations for temperate species. Prior to their seaward migration, silver eels are often subject to many anthropogenic impacts in freshwater environments, and these can negatively impact both the quantity (Dekker, ) and quality (Béguer‐Pon et al., ) of silver eels escaping to sea. Hydroelectric dams, in particular, can cause delays to downstream migrations and high mortality of eels that enter station intakes (Richkus & Dixon, ).…”

“…While the timing of downstream passage and egress to the sea have been widely researched (e.g. van den Thillart, Dufour, & Rankin, 2009; Béguer‐Pon et al., ; Bultel et al., ), fine‐scale movements of silver eels of any species prior to embarking on their seaward migration have not been studied.…”