149 



The relationship between smolt and postsmolt 

 growth for Atlantic salmon iSalmo salar) in the 

 Gulf of St. Lawrence 



Kevin D. Friedland 



UMass/NOAA Cooperative Marine Education and Research Program 



Blalsdell House 



University of Massachusetts 



Amherst, Massachusetts 01003 



Present address: National Marine Fisheries Service 



28 Tarzwell Dr 



Narragansett, Rhode Island 02882 

 E-mail address: kevinfriedlandiginoaagov 



Lora M. Clarke 



Department of Natural Resources Conservation 

 Holdsworth Hall 

 University of Massachusetts 

 Amherst, Massachusetts 01003 



Jean-Denis Dutil 



Ministere des Peche et des Oceans 

 Institut Maurice-Lamontagne 

 850 route de la Mer, Mont-Joli 

 Quebec, G5H 3Z4, Canada 



Matti Salminen 



Finnish Game and Fisheries Research Institute 



Viikinkaari 4 



P.O. Box 2, FIN-00791 



Helsinki, Finland 



The interaction of ocean climate 

 and growth conditions during the 

 postsmolt phase is emerging as the 

 primary hypothesis to explain pat- 

 terns of adult recruitment for indi- 

 vidual stocks and stock complexes 

 of Atlantic salmon (Sabno salar). 

 Friedland et al. (1993) first reported 

 that contrast in sea surface tempera- 

 ture (SST) conditions during spring 

 appeared to be related to recruitment 

 of the European stock complex. This 

 hypothesis was further supported 

 by the relationship between cohort 

 specific patterns of recruitment for 

 two index stocks and regional scale 

 SST (Friedland et al., 1998). One of 

 the index stocks, the North Esk of 

 Scotland, was shown to have a pat- 

 tern of postsmolt growth that was 

 positively correlated with survival. 



indicating that growth during the 

 postsmolt year controls survival and 

 recruitment (Friedland et al., 2000). 

 A similar scenario is emerging for 

 the North American stock complex 

 where contrast in ocean conditions 

 during spring in the postsmolt migra- 

 tion corridors was associated with 

 the recruitment pattern of the stock 

 complex (Friedland et al., 2003a, 

 2003b). The accumulation of addi- 

 tional data on the postsmolt growth 

 response of both stock complexes will 

 contribute to a better understanding 

 of the recruitment process in Atlantic 

 salmon. 



Anadromous salmonids produce co- 

 horts of juvenile smolts that migrate 

 over a short period of time at a nearly 

 uniform size; however, the variability 

 that occurs in migration timing and 



the size spectra of smolts is of poten- 

 tial interest in the study of recruit- 

 ment (Hoar, 1976; Wedemeyer et al., 

 1980). Enhancement and restoration 

 programs provide data on the effect 

 of smolt size on return rate where 

 hatchery practices both intentionally 

 and unintentionally produce fish of 

 varying size and quality. There are 

 many case studies that show positive 

 correlations between smolt size and 

 return rate in salmonids, but non- 

 significant relationships have also 

 been observed, which underscore 

 the fact that the contrast in size 

 that can be achieved in hatcheries 

 is often outside ecologically relevant 

 limits (Farmer, 1994; Salminen et 

 al., 1994). The functional relation- 

 ship between smolt size and return 

 rate is probably more accurately de- 

 scribed as nonlinear and as having 

 some optimality within the range of 

 hatchery releases (Bilton et al., 1982; 

 Henderson and Cass, 1991). 



Researchers have also considered 

 the effect of smolt size at ocean entry 

 and the effect of smolt size on the en- 

 suing growth patterns of postsmolts. 

 Ward and Slaney (1988) described a 

 positive relationship between return 

 rate and smolt size for rainbow trout 

 iSaliJio gairdneri). suggesting that 

 the recruitment rate of a year class 

 was mediated by the mortality that 

 occurred when the fish migrated to 

 sea. When new data were added to 

 that relationship, the original con- 

 clusions were no longer supported, 

 indicating that factors other than 

 smolt size at ocean entry contribute 

 to recruitment (Ward, 2000). Al- 

 though size at ocean entry may con- 

 tribute to mortality risk, postsmolt 

 growth, and the biotic and abiotic 

 factors affecting postsmolt growth, 

 often play a dominant role (Salmin- 

 en et al., 1995). However, what has 

 remained obscure is whether size 

 at ocean entry influences postsmolt 

 growth. Skilbrei (1989) and Nicieza 

 and Branfia (1993) reported negative 

 relationships between smolt size and 



Manuscript submitted 4 February 2004 to 

 the Scientific Editor's Office. 



Manuscript approved for publication 

 10 April 2005 by the Scientific Editor. 



Fish. Bull. 104:149-155 (2006). 



