Date of Award

1985

Degree Type

Thesis

Degree Name

Master of Science in Zoology

Department

Zoology

First Advisor

William H. Krueger

Abstract

Progressive epidermal pigmentation of Anguilla rostrata elvers in a coastal Rhode Island stream was essentially identical to that described for A. anguilla, and proceeded rapidly in freshwater. Earlier arriving elvers averaged larger than those arriving later in the season, paralleling studies of European elvers. Mean total lengths of elvers collected in 1984 were significantly greater than those for 1983 and are the largest recorded for the Western North Atlantic. These differences may be due to sampling technique. Migration of elvers into freshwater may be induced by decreasing flow rates and/or increasing stream temperatures. The relatively slow upstream migration of elvers in the lower section of the stream (approximately 200 m per month) is attributed to high stream gradient and the presence of obstructions. By late summer and early fall, elvers (age I+) had acquired the coloration typical of yellow eels and had grown 20 to 30 mm larger than elvers arriving in freshwater in late winter and spring. The frequency of II+ and older eels increased with increasing distance from the tidal zone. This indicates that the upstream migration of elvers is limited, and that the colonization of inland waters is accomplished mainly by yellow eels in their second and later years of continental life.

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