, Volume 68, Issue 4, pp 339-348

Elver Invasion, Population Structure and Growth of Marbled eels Anguilla marmorata in a Tropical River on Réunion Island in the Indian Ocean

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Abstract

Invasion mechanisms of Anguillid eels in tropical freshwater systems have seldom been described but are supposed to be similar to those of temperate eels. We used electrofishing and continuous trapping to define recruitment dynamics in spatial and temporal organization of marbled eels, Anguilla marmorata, in the Mat River, Réunion Island, Indian Ocean. Upstream migration of A. marmorata elvers lasted all year long, with a marked enhancement from January to April. We observed six successive length-classes during the 8 months period from December 2000 to July 2001, corresponding to the successive estuarine recruitments of elvers, of which three happened during the study. Mean growth estimation (15.3±3.5 mm month−1), calculated by linking modal-classes in length–frequency polynomial compositions of electrofishing data was corroborated by otolithometry performed on eels collected in the trap (17.4 ± 3.4 mm month−1). Migrant elvers (mean length 117.3 ± 24.6 mm) invaded the middle stream course 2, 3 or 4 months after they entered the river system. This is a marked difference from temperate Anguilla species that grow more slowly and usually reside 1 year downstream before they migrate or settle. Moreover, upstream invasion patterns of A. marmorata elvers in this tropical river appear to be synchronized with regular cyclonic floods occurring in the Indian Ocean.