Since inferring spawning areas from larval distributions in the Sargasso Sea a century ago, the oceanic migration of adult American eels has remained a mystery. No adult eel has ever been observed migrating in the open ocean or in the spawning area. Here, we track movements of maturing eels equipped with pop-up satellite archival tags from the Scotian Shelf (Canada) into the open ocean, with one individual migrating 2,400 km to the northern limit of the spawning site in the Sargasso Sea. The reconstructed routes suggest a migration in two phases: one over the continental shelf and along its edge in shallow waters; the second in deeper waters straight south towards the spawning area. This study is the first direct evidence of adult Anguilla migrating to the Sargasso Sea and represents an important step forward in the understanding of routes and migratory cues.
In an attempt to document the migratory pathways and the environmental conditions encountered by American eels during their oceanic migration to the Sargasso Sea, we tagged eight silver eels with miniature satellite pop-up tags during their migration from the St. Lawrence River in Québec, Canada. Surprisingly, of the seven tags that successfully transmitted archived data, six were ingested by warm-gutted predators, as observed by a sudden increase in water temperature. Gut temperatures were in the range of 20 to 25°C—too cold for marine mammals but within the range of endothermic fish. In order to identify the eel predators, we compared their vertical migratory behavior with those of satellite-tagged porbeagle shark and bluefin tuna, the only endothermic fishes occurring non-marginally in the Gulf of St. Lawrence. We accurately distinguished between tuna and shark by using the behavioral criteria generated by comparing the diving behavior of these two species with those of our unknown predators. Depth profile characteristics of most eel predators more closely resembled those of sharks than those of tuna. During the first days following tagging, all eels remained in surface waters and did not exhibit diel vertical migrations. Three eels were eaten at this time. Two eels exhibited inverse diel vertical migrations (at surface during the day) during several days prior to predation. Four eels were eaten during daytime, whereas the two night-predation events occurred at full moon. Although tagging itself may contribute to increasing the eel's susceptibility to predation, we discuss evidence suggesting that predation of silver-stage American eels by porbeagle sharks may represent a significant source of mortality inside the Gulf of St. Lawrence and raises the possibility that eels may represent a reliable, predictable food resource for porbeagle sharks.
Large‐scale habitat use and movements of yellow American eels (Anguilla rostrata) from the St. Lawrence River were examined using acoustic telemetry from early summer to late fall in 2010 and 2011. Sixty‐seven eels were tagged, and their passage or presence was recorded using fixed acoustic arrays covering a 400 km distance along the St. Lawrence River and Estuary. Sixty‐four per cent of the 67 tagged eels were detected. Most eels were detected at only one array; the closest to their release location and at several occasions during the tracking period, suggesting a high proportion of freshwater residency in the upstream part of the St. Lawrence River. Downstream movements towards the brackish estuary (63–418 km distance) were demonstrated for 16.4% of the eels, particularly for those caught at the most downstream site that is close to the brackish estuary. Our results strongly suggest a lower activity of freshwater resident yellow eels during summer, a behaviour that may be related to day length, which defines time available for their nocturnal foraging. Indeed, yellow eels were detected primarily at night; no effect of moon phase was revealed. Movements in the vicinity of arrays (up to 116 km in the fluvial estuary) were suggested and smaller‐scale movements within Lac St. Louis were demonstrated, highlighting a yellow‐eel home range far more extensive than previously reported in smaller systems. Evidence for within‐season homing and site fidelity is also reported.
The American eel is a widely distributed, facultatively catadromous fish that is reported to range from southern Greenland to the Gulf of Mexico and Caribbean Sea. Despite such a broad distribution, our understanding of the species' biology and ecology is based on research carried out almost exclusively in Canada and the United States. As one moves south from the United States through both the Antilles and Mexico, progressively less is known about the species. Even farther south, in Central and South America, information is sufficiently scant as to raise doubt on whether or not the species occurs there at all. This study compiled available quantitative information from literature and museum records and qualitative information from other literature and personal contacts on the distribution of the American eel from Mexico, Central America, northern South America, and the Antilles, to provide the first comprehensive description of the species' historical and current distribution in the region. The results of this investigation confirm that the American eel was historically, and continues to be, widely distributed throughout the Wider Caribbean region, extending all the way to eastern Venezuela and the island of Trinidad. Furthermore, this work also addresses habitat loss and degradation, pollution, and increasing pressure from developing commercial fisheries as the major threats facing the species both locally in, and broadly throughout, the region. If effective management and conservation of the panmictic American eel is to be achieved, it is of critical importance that greater efforts be made to promote and encourage research on the species' basic ecology in the Wider Caribbean region.
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.
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