Within-river variation in seasonal growth trajectories of juvenile Atlantic salmon (Salmo salar)

• Main Author: Strothotte, Eva
• Format: Thesis
• Language: English
• Published: 2002
• Subjects: Atlantic salmon; Salmo salar
• Online Access: https://oceanrep.geomar.de/id/eprint/3360/; https://oceanrep.geomar.de/id/eprint/3360/1/Dipl.%202002%20Strothotte,%20E.pdf

Atlantic salmon (Salmo salar L.) populations are in severe decline over most of their range since the 1980s. Climate change may modify life pattems on a global scale and and possible reductions in growth of cold-water fish species such as salmon. Variations in growth of juvenile salmon among tributaries within an individual river system and the factors which may condition the growth and size-at-age have not been extensively studied. In this thesis seasonal growth trajectories were examined of three age classes of juvenile Atlantic salmon from two stream types (main stem, tributary) and two branches in a medium size Atlantic salmon river (Margaree River) in eastem Canada. Annual variations in size-at-age of juveniles were examined over a ten-year period. Periodic deposition of minerals characterized as circuli, on the scales are used to describe the growth histories of the juveniles. Finally, the growth histories of juveniles are used to confirm the commonly held view that smoltification in Atlantic salmon is a process defined by the attainment of a threshold length. There was large among tributary variation in mean fork length of juveniles with important variations within a sampling site. Sampling date was the most important explanatory variable for fork length of fry. Sampling site and intra-cohort effects were important explanatory variables for variation in fork length of age-1 parr. Correlations between fork length of the fish and year were higher than between fork length and cohort, indicating that current environmental conditions have more significant effects on size parr than the conditions encountered by the cohort in the previous year. Especially interesting in this study were the fish of the Northeast-tributary I and the Southwest-tributary I since they show different growth patterns, with fish in the Southwest-tributary showing a linear growth through the season while fish in the Northeast-tributary I slowed down in the fall, although the temperature regimes at those sites were essentially identical. ...