Distribution of Leptocephali of the Oceanic Species Derichthys Serpentinus and Nessorhamphus Ingolfianus (Family Derichthyidae) in the Western Sargasso Sea in Relation to Physical Oceanography
Abstract:Leptocephali are the morphologically unusual, epipelagic, oceanic larval stages of two orders of eel-like fishes, the adults of which range in distribution from meso- and bathy-pelagic (Derichthyidae) to continental freshwater (Anguillidae). This study determined the distributions and abundances of two of the most abundant leptocephali, Derichthys serpentinus and Nessorhamphus ingoljianus (Derichthyidae) in the western Sargasso Sea in summer and fall, related the distributions to oceanic features, and contrasted the distributions with those of Anguilla rostrata and A. anguilla (Anguillidae) with respect to retention in the oceanic realm. Leptocephali were sampled with a 3-m Isaacs Kidd Midwater Trawl (1.8-mm mesh) along a transect from the Gulf Stream southeastward into the Sargasso Sea (summer and fall) and from the Bahamas northeastward to the transect line (fall). In summer derichthyid leptocephali were essentially absent from the Gulf Stream but were quite abundant just east of the Stream. D. serpentinus were abundant all along the rest of the transect, but N. ingoljianus became rare southeast of a sharp frontal zone. Anguilla species became more abundant southeast of the front. In fall D. serpentinus and A. anguilla were still absent from the Gulf Stream and the Providence Channel of the Bahamas though widespread elsewhere, A. rostrata was present in the Gulf Stream, the Bahamas and the open ocean. Few N. ingoljianus leptocephali were caught as most had probably already metamorphosed. It is hypothesized that a more northerly distribution of spawning of N. ingoljianus than Anguilla and an earlier metamorphosis favor oceanic retention of the former. That does not explain oceanic retention of D. serpentinus. The presence of all four species in high concentration just east of the Gulf Stream and the apparent differential entry into the Stream suggests that other physical features or behavioral differences may be important.
Document Type: Research Article
Publication date: November 1, 1987
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