472 



Abstract.— We examined scale samples 

 from historical collections of postsmolts 

 from the Gulf of St. Lawrence, Canada, 

 with the aim of understanding the role 

 of estuarine and coastal habitats as a 

 juvenile nursery for Atlantic salmon. 

 Circuli spacing patterns were extracted 

 from the scales of 580 postsmolts col- 

 lected in the Gulf during three seasons, 

 1982-84. Poststratification of the 

 samples by collection date within year 

 suggests that in some years postsmolts 

 remain in the Gulf throughout the en- 

 tire summer growth season, whereas in 

 other years only slower growing fish re- 

 main in these areas. Growth patterns 

 for Gulf of St. Lawrence postsmolts 

 were compared with patterns for re- 

 turns from three salmon stocks from 

 the southern end of the range in North 

 America. These data suggest that in 

 some years postsmolt growth in the 

 Gulf is as robust as that observed for 

 both the one seawinter ( ISW) and two 

 seawinter (2SW) returns to southern 

 rivers. Postsmolts are believed to use 

 oceanic nursery areas generally; thus, 

 comparable growth between the two 

 stock groups suggests that the Gulf 

 may serve as an important part of the 

 postsmolt nursery range in some years. 

 The concept of the postsmolt nursery 

 as a continuum between neritic and 

 oceanic areas is essential to evaluating 

 ocean climate and productivity effects 

 on salmonid recruitment. 



Growth patterns in postsmolts and 



the nature of the marine juvenile nursery 



for Atlantic salmon, Salmo salar 



Kevin D. Friedland 



UMass/NOAA CMER Program 



Blaisdell House, University of Massachusetts 



Amherst, Massachusetts 01003 



E-mail address friedlandkd forwild umassedu 



Jean-Denis Dutil 



Ministere des Peches et des Oceans 



Institut Maurice-Lamontagne 



850 route de la Mer, Mont-Joli, Quebec, Canada G5H 3Z4 



Teresa Sadusky 



National Marine Fisheries Service, NOAA 



166 Water Street 



Woods Hole, Massachusetts, 02543 



Manuscript accepted 11 August 1998. 

 Fish. Bull. 97:472-481 ( 1999). 



Anadromous salmonids, such as 

 Atlantic salmon, Salmo salar, use 

 freshwater stream habitats as nurs- 

 ery areas for their early life history 

 stages (Thorpe, 1994). Freshwater 

 residency provides refuge from po- 

 tential predators and relatively 

 stable survival conditions for eggs 

 and juveniles (Chaput et al., 1998). 

 Thus, the recruitment of smolts 

 during the freshwater phase is char- 

 acterized by relatively low annual 

 variability, most of which is attrib- 

 uted to the size of spawning escape- 

 ments (Chadwick, 1987). As a con- 

 sequence, the relationships between 

 spawning stock abundance and re- 

 cruits migrating from freshwater 

 take on predictable forms (Chad- 

 wick, 1985; Elliott, 1993). The rela- 

 tionships between generations of 

 spawners, however, are not as clear 

 owing to highly variable rates of 

 marine survival. 



The first year at sea, or the post- 

 smolt year, for Atlantic salmon is 

 poorly understood. The transition to 

 the marine environment is in itself 

 a survival challenge associated with 

 specific estuarine habitats (Levings, 

 1994). After postsmolts make the 



transition, they are believed to dis- 

 perse widely in ocean surface wa- 

 ters. This belief stems from the facts 

 that they are rarely caught in near- 

 shore fishing gears and have proven 

 difficult to capture in directed sur- 

 veys. The exception has been in the 

 Baltic area, where the spatial con- 

 fines of the Baltic Sea and postsmolt 

 recoveries in commercial fisheries 

 have combined to produce a relative 

 wealth of information on the distri- 

 bution and survival of postsmolts in 

 that region (Larsson, 1985; Eriks- 

 son 1994; Kuikka and Salminen 

 1994). The equivalent information 

 does not exist for North Atlantic 

 postsmolts; thus, it is critical to 

 learn more about the basic biology 

 of postsmolts so that informed in- 

 terpretations of the patterns in 

 salmonid population dynamics can 

 be made. 



Recoveries of North American 

 versus European postsmolts sug- 

 gest that habitat use and ecological 

 roles may differ for the early ma- 

 rine stages of the two stock com- 

 plexes. Recent captures of posts- 

 molts in the Northeast Atlantic 

 show that they are distributed over 



