Species assemblages of leptocephali in the southwestern Sargasso Sea

Abstract

Catches of leptocephali of shelf and slope marine eels of the Chlopsidae, Congridae, Moringuidae, Muraenidae, and Ophichthidae collected during a survey in the southwestern Sargasso Sea in late September and early October 1984 were analyzed to learn about their reproductive ecology and larval transport. Sampling along a transect from the Florida Current (FC) out across the southwestern Sargasso Sea and in the Northwest Providence Channel (NWPC) of the Northern Bahamas enabled the evaluation of the larval distributions, abundances and size ranges, regional assemblage structure, and the apparent spawning areas of these marine eels. Distinctly different assemblages observed in the FC and NWPC included the congrid genera Heteroconger, Paraconger, Uroconger, and many ophichthid species, which were rare or absent offshore. Other taxa of congrids, chlopsids, muraenids and moringuids were present in all areas, but the smallest specimens of most taxa were only caught at the NWPC or FC stations. Multivariate analyses reflected higher richness and abundance in the FC and NWPC and also similar species compositions in offshore areas. The patterns of distribution of these leptocephali differed from those of anguillid, nettastomatid, and mesopelagic eel leptocephali collected in the same survey. These findings support the hypothesis that most taxa of marine eels spawn close to their adult habitats, and indicate that despite high biodiversity of marine eels in the Northern Bahamas, only some species of leptocephali appear to get transported far offshore by ocean currents.

Ecology of Anguilliform Leptocephali: Remarkable Transparent Fish Larvae of the Ocean Surface Layer

“…45). Anguillid , derichthyid (Castonguay and McCleave 1987b), and nemichthyid (Wippelhauser et al 1996) leptocephali were also abundant offshore in this transect across the southwest Sargasso Sea (Miller and McCleave 2007).…”

“…Similarly, leptocephali of congrid, chlopsid, muraenid, and ophichthid eels were very abundant in the Northwest Providence Channel of the Northern Bahamas at the southwest edge of the Sargasso Sea in the western North Atlantic (Fig. 45;Miller and McCleave 2007). However, there are often strong currents adjacent to the these high density concentrations of leptocephali, such as the Kuroshio Current in the East China Sea and the Florida Current (southern part of the Gulf Stream) adjacent to the northern Bahamas, which likely transport many leptocephali further offshore.…”

“…For example, although derichthyid leptocephali were abundant in the summer and fall across the southwest Sargasso Sea (Castonguay and McCleave 1987b), they were absent in the same general region in the winter and spring . The opposite pattern was observed for Serrivomer leptocephali, which were abundant in the winter and spring , but almost completely absent in the summer and fall (Miller and McCleave 2007). Other species are present in both seasons, so more research is needed to gain a better understanding of the many factors that can affect the zoogeography and temporal occurrence of leptocephali.…”

“…Collections of leptocephali over or near shelf areas or around islands also have shown that most shallow water marine eels do not migrate very far offshore to spawn. The exact spawning areas of marine eels are generally not known, but the smallest leptocephali of most shallow water eels are typically collected over or near the edge of the continental shelf (Castle and Roberston 1974;Miller et al 2002a; or in close proximity to shallow water habitats (Castle 1968;Miller 1995Miller , 2002bMiller et al 2002aMiller et al , 2006aMiller and McCleave 2007), suggesting nearby spawning areas.…”

“…In a survey for leptocephali that included a transect across the southwest Sargasso Sea and stations within and near the northern Bahamas (Miller and McCleave 2007), clearly different patterns of distribution and regional size of leptocephali were observed for some species (Fig. 45).…”