The spawning areas of the Atlantic freshwater eels were discovered about a century ago by the Danish scientist Johannes Schmidt who after years of searching found newly hatched larvae of the European eel, Anguilla anguilla, and the American eel, Anguilla rostrata, in the southern Sargasso Sea. The discovery showed that anguillid eels migrate thousands of kilometers to offshore spawning areas for reproduction, and that their larvae, called leptocephali, are transported equally long distances by ocean currents to their continental recruitment areas. The spawning sites were found to be related to oceanographic conditions several decades later by German and American surveys from 1979 to 1989 and by a Danish survey in 2007 and a German survey in 2011. All these later surveys showed that spawning occurred within a restricted latitudinal range, between temperature fronts within the Subtropical Convergence Zone of the Sargasso Sea. New data and re-examinations of Schmidt's data confirmed his original conclusions about the two species having some overlap in spawning areas. Although there have been additional collections of leptocephali in various parts of the North Atlantic, and both otolith research and transport modelling studies have subsequently been carried out, there is still a range of unresolved questions about the routes of larval transport and durations of migration. This paper reviews the history and basic findings of surveys for anguillid leptocephali in the North Atlantic and analyses a new comprehensive database that includes 22612 A. anguilla and 9634 A. rostrata leptocephali, which provides a detailed view of the spatial and temporal distributions and size of the larvae across the Atlantic basin and in the Mediterranean Sea. The differences in distributions, maximum sizes, and growth rates of the two species of larvae are likely linked to the contrasting migration distances to their recruitment areas on each side of the basin. Anguilla rostrata leptocephali originate from a more western spawning area, grow faster, and metamorphose at smaller sizes of <70 mm than the larvae of A. anguilla, which mostly are spawned further east and can reach sizes of almost 90 mm. The larvae of A. rostrata spread west and northwest from the spawning area as they grow larger, with some being present in the western Caribbean and eastern Gulf of Mexico. Larvae of A. anguilla appear to be able to reach Europe by entering the Gulf Stream system or by being entrained into frontal countercurrents that transport them directly northeastward. The larval duration of A. anguilla is suggested to be quite variable, but gaps in sampling effort prevent firm conclusions. Although knowledge about larval behaviour is lacking, some influences of directional swimming are implicated by the temporal distributions of the largest larvae. Ocean-atmosphere changes have been hypothesized to affect the survival of the larvae and cause reduced recruitment, so even after about a century following the discovery of their spawning areas, mysteries still rema...

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A pelagic, long‐lived leptocephalus is common to families of eels, whether the juveniles inhabit the open ocean, shelf waters, or estuarine and fresh waters. Successful leptocephali of continental species must leave the open ocean, while those of oceanic species must avoid advection from the open ocean. The movements of leptocephali of migratory species should be considered conceptually as a dispersal‐mortality problem. On the basis of the distribution of small (recently hatched) leptocephali, the Sargasso Sea in the western North Atlantic Ocean is identified as a spawning area for the catadromous American and European (angui llid) eels, western Atlantic shelf‐dwelling Conger eels, and numerous oceanic species, e.g. Nemichthys scolopaceus, Serri voiner beanii, Derichthys serpentinus and Nessorhamplms ingolfianus. Within the Sargasso Sea, the Subtropical Convergence Zone is a narrow latitudinal zone where northern and southern bands of thermal density fronts occur, especially in winter. Spawning of the two catadromous eels and the two western conger eels seems to be limited to areas in or south of the southern band of fronts, where southern Sargasso Sea water occurs. Spawning of most of the oceanic species occurs on both sides of these fronts. Some feature of the frontal zone or the southern waters, such as odour, may serve as a signal to trigger cessation of migration and initiation of spawning in catadromous eels. Thus the source of leptocephali of the two species of Anguilla may be zotially restricted. Because of confluence of water into fronts and resulting eastward jet‐like currents, fronts may be sinks for a portion of the leptocephali of numerous shelf‐dwelling species, which may be advected away from suitable juvenile habitat. The size distributions of leptocephali suggest that gyres in the southwestern Sargasso Sea, an Antilles Current, and the Florida Current north of the Bahamas are routes of exit for anguillid and congrid eels. Shorter larval duration and more northerly spawning facilitates retention of the oceanic species D. serpentinus and N, ingolfianus in the western Sargasso Sea. Shorter duration of the leptocephalus stage of the American eel than the European eel, and plasticity in length of time prior to metamorphosis in both American and European eel leptocephali cause most leptocephali drifting on the Gulf Stream‐North Atlantic Current system to arrive at the appropriate continent. This current system does transport both species, but most American eel leptocephali are found only in the west, while European eel leptocephali are found all across the North Atlantic current and its branches. A dine of increasing lengths of European eel leptocephali from south to north off the continent of Europe has been used as evidence that drift on the North Atlantic Current cannot be the transport mechanism and that active swimming must occur. Recent indications are that there is northward transport of water in the Canary Basin. Eastward jets in the Sargasso Sea and evidence for a basin‐wide eastward countercu...