NOTE Fnedland et al : Relationship between smolt and poslsmolt growth in Salmo solar 



153 



Atlantic salmon may arise from geographical dif- 

 ferences or year-to-year changes (or both) in prey 

 regimes during the critical diet-transition period. 

 In lake-run brown trout, Niva and Jokela (2000) 

 found a positive correlation between hatchery 

 growth rate and postsmolt growth in a lake with 

 small fish as the main prey. In contrast, hatchery 

 growth did not predict growth in a lake where the 

 fish had to prey on bottom-dwelling invertebrates. 

 This finding may indicate that assessment of in- 

 dividual performance may be highly specific to 

 environments in migratory salmonids. 



Size of postsmolts at ocean entry in salmonids 

 also manifests itself in predictable patterns of life 

 history variation. In sea trout (Salmo triitta) there 

 is a close correspondence between size of juvenile 

 stage and adult size, which is believed to have an 

 impact on recruitment through size variation at 

 critical life stages (Elliott, 1985). Hutchings and 

 Jones (1998) found that smolt age and size had 

 a small effect on the growth-rate threshold for 

 maturity in Atlantic salmon. Smolt-size variation 

 in sea trout has been associated with latitude, 

 indicating that for this species recruitment strate- 

 gies are likely adapted to local physical conditions, 

 predators, and prey regimes (L' Abee-Lund et al., 

 1989). Wild smolts are often smaller than hatch- 

 ery smolts for the same or allied strains, yet they 

 consistently survive at higher rates (Poole et al., 

 2003). Obviously there are other cofactors that can 

 explain why the wild fish overcome any advantage 

 conferred on hatchery fish by their larger size at 

 migration. The wild versus hatchery comparison 

 is a relatively weak piece of evidence to use to 

 dismiss the idea that smolt size is an important 

 survival factor. However, a recent study of size at 

 ocean entry in a Quebec stock of wild fish may 

 provide more useful evidence (Dodson^ Caron-). 

 The investigators found that the size spectra of 

 smolts were not different from the size spectra of 

 back-calculated smolt sizes for returning adults, 

 suggesting some factor other than size at ocean 

 entry was controlling survival. It should be noted 

 that postsmolts collected in the present study were 

 of unknown origin, but the scale pattern for the 

 freshwater zone clearly indicates that they were 

 of wild origin. 



The growth response of postsmolts may be gov- 

 erned by a simple response to temperature optima 

 occurring in coastal marine waters, but it may al- 

 so be more complex than that. The surface waters 

 in the Gulf of St. Lawrence circulate in wide-scale 



Dodson, J. 2004. Personal comniun. Departement 

 de Biologie Pavilion Alexandre-Vachon, local .30.58-B 

 Universite Laval, Quebec, GIK 7P4. Canada. 

 Caron. F. 2004. Personal commun. Direction de 

 la Recherche Faune et Pares Quebec, 67.5 est, Boul. 

 Rene-Levesque Boite 92, lie etage, Quebec, GIR .5V7, 

 Canada. 



012- 



0-10- 



0.08- 



0.06- 



0,04- 



1982 

 1983 

 1984 

 -1982 

 1983 

 1984 



0.02-1 1 1 1 1 1 1 1 1 1 r 



0.02 0.04 0,06 0.08 010 12 



Circuli spacing, early marine period (mm) 



Figure 4 



Relationships between circuli spacing during the summer 

 marine period and circuli spacing during the early marine 

 period for Atlantic salmon (Salinn salar) in the Gulf of St. 

 Lawrence. 



e 9 



03- 



Freshwater 

 Marine 



•»•••• . . • ' 



« z: 





Aug 6 



Aug 20 



Sep 3 Sep 17 



Date of capture 



— r- 

 Oct • 



Figure 5 



Freshwater zone length and marine zone length, by date of 

 capture during the 1982 field season for Atlantic salmon t Salmo 

 salar) in the Gulf of St. Lawrence. 



