Body and scale growth of wild Atlantic salmon smolts during seaward emigration

Abstract

The relationship between scale and body growth for emigrating Atlantic salmon, Salmo salar, smolts was previously not understood and therefore was examined in this study using mark-recapture techniques. The size of smolts at time of recapture was significantly greater than when marked (P = 0.0002). The growth in length of smolts emigrating 5 km over an average of 20 days was 7.7 ± 6.1 mm per day. Instantaneous somatic growth (Gbody) ranged from 7.0 × 10−4 to 5.1 × 10−3 (mean = 2.7 × 10−3 ± 1.3 × 10−3). The mean number of plus growth circuli present per scale was significantly greater for smolts when recaptured compared to when marked (P = 0.0014). The instantaneous growth rate of scales (Gscale) ranged from 1.4 × 10−3 to 11.5 × 10−3 (mean = 6.6 × 10−3 ± 4.3 × 10−3). The relationship between body size and scale radius showed positive allometry rather than isometry. The relationship of Gscale with Gbody showed positive allometry indicating that scales grew at a slightly faster rate than the body during the emigratory period.