Migrating American Eels in Nova Scotia

Abstract American eels Anguilla rostrata harvested from weirs by the commercial fisheries of three Nova Scotian rivers differed in life history characteristics. Depending upon their orientation, weirs captured either downstream‐migrating silver American eels or upstream‐migrating yellow American eels. Mean lengths and weights of downstream‐migrating American eels differed among rivers, increasing as the run progressed from late August to mid‐November. Sexually maturing (silver) migrants were larger (typically exceeding 400 mm in length) and older than immature nonmigrants and had a higher ovarian gonadosomatic index (proportion of body weight contributed by ovaries; usually above 1.5%). At a given length, silver eels had larger eye‐diameter indices (eye width x eye height) than did yellow eels but, for silver eels, eye index was not a predictor of gonadosomatic index. Silver eels migrating later in the run were more mature (had higher gonadosomatic indices) than those migrating earlier. Silver eels from different rivers were similar in age and gonadosomatic index. Male silver eels were smaller, less mature, and migrated earlier than did most females. Skin coloration (yellow‐silver) was a fairly reliable guide to sexual maturity (immature‐maturing), but histologically detectable maturation may begin one or more years prior to coloration change and participation in the spawning migration.