Pigmentation, size, and migration of elvers (Anguilla rostrata (Lesueur)) in a coastal Rhode Island stream

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Abstract
Progressive pigmentation of Anguilla rostrata elvers was very similar to that described for A. anguilla. Pigmentation increased rapidly with the advancing season, while total length decreased. The increase in pigmentation was independent of the decrease in length and may have been influenced by increased contact with the substrate. Mean lengths showed significant differences within seasons and between years, and the range of variation was greater than that described by V.D. Vladykov (1966. Verh. Int. Ver. Theor. Angew. Limnol. 16:1007-1017) for elvers collected from Maryland to Quebec [Canada]. We substantiate Vladykov''s finding that elver size tends to increase with increasing distance from the spawning area, but reject his size-sex hypothesis. The main migration occurred in April and May and was related to decreasing water depth and rising stream temperature. Elvers took about 4 weeks to ascend 180 m above the tidal zone, probably because of a high stream gradient and the absence of tidal influence.