Hatching time and larval growth of Atlantic eels in the Sargasso Sea

Several surveys and studies have examined the Atlantic anguillid eels’ larval distributions, but little is known about their larval growth rates. Otoliths of 17 European eel Anguilla anguilla (8.8–46.0 mm) and 19 American eel Anguilla rostrata (9.8–59.9 mm) leptocephali collected in the Sargasso Sea (25–31°N, 58–70°W) in March and April 2011 were analyzed and their spawning times and larval growth rates were estimated. Ages calculated from the number of otolith increments of European and American eel larvae showed ranges of 10–127 days and 14–233 days, respectively. Linear relationships between age and total length indicated early larval growth rates of 0.31 mm/day for the European eel and 0.35 mm/day for the American eel. This suggested slower growth rates in low temperatures in the Sargasso Sea compared to other anguillid species in the Indo-Pacific, where water temperatures are higher. The back-calculated hatching dates of small leptocephali (8.8–26.7 mm) were in February and March 2011. More American eels hatched in February and more European eels hatched in March. The hatching times of two larger European eel leptocephali (38.7 and 46.0 mm) and a larger American eel leptocephalus (59.9 mm) were back-calculated to November and December 2010 and July 2010, respectively, suggesting hatching times outside of the primary spawning seasons. These novel observations provide important information on the timing of spawning and larval growth characteristics of Atlantic eels, which would benefit from validation by additional otolith studies of leptocephali.