Length Characteristics of Smolts and Timing of Downstream Migration among Three Strains of Atlantic Salmon in a Southern New England Stream

As part of a program to restore Atlantic salmon Salmo salar to the Connecticut River system, 10 year‐classes of fry were stocked to produce smolts in Sandy Brook, Connecticut. During 1980–1986, fry were obtained from sources outside of the Connecticut River system; a geographically distant stain from Iceland was stocked in three of the years (1980, 1981, 1983), and the Penobscot strain, which originated from several rivers in Maine, was stocked in four of the years ( 1982, 1984, 1985, 1986). As restoration efforts continued, fry originating from adults that had returned to the Connecticut River were stocked in the final three years (1988, 1989, 1991). Although all strains produced a predominance of age‐1 and age‐2 smolts, length characteristics of smolts differed among strains. Total lengths of Icelandic smolts averaged 9–11 mm smaller at emigration at age 1 and 13–21 mm smaller at emigration at age 2 than both New England strains. Based upon minimum lengths that 95% of all smolts attained the previous growing season, most Icelandic parr smolted if they reached 87 mm at the end of their first growing season or 130 mm at the end of their second growing season. In contrast, most New England smolts had attained total lengths of 113 mm and 147 mm by the end of their first and second growing seasons, respectively. Icelandic age‐1 smolts also migrated up to 2 weeks later and at mean water temperatures 3°C higher than New England age‐1 smolts. The late migration of small Icelandic smolts may not be appropriate for successful emigration from southern New England streams.