»78 



Fishery Bulletin 97(3), 1999 



ming potential of the fish (Reddin and 

 Friedland, 1993). As such, postsmolt mi- 

 gration routes are unlikely to be equiva- 

 lent among years (Caron, 1983; Jonsson 

 et al., 1993). At some point during the 

 postsmolt's first growing season, swim- 

 ming ability begins to exceed current ve- 

 locity and postsmolts can more effectively 

 modify their distribution according to 

 preferences driven by migi-ation mecha- 

 nisms or foraging behavior. These factors 

 may allow postsmolts to concentrate in 

 specific habitats that best suit their feed- 

 ing requirements and afford them some 

 measure of protection from predation. 

 However, the process of habitat selection 

 may result in a nursery that encompasses 

 different areas each year and thus not 

 linked to a specific area (Friedland et al., 

 1996a). Therefore, years of poor feeding 

 and growth conditions in the Gulf of St. 

 Lawrence do not necessarily mean poor 

 sui'vival conditions because they do not 

 preclude the use of other neritic areas as 

 postsmolt nursery. For example, in some 

 years the nursery may form along the 

 south coast of Newfoundland or for that 

 matter make use of few neritic habitats 

 as the fish distribute in offshoi'e areas. 



Contemporary characterizations of 

 postsmolt populations may be inadequate 

 if they fail to account for the distribution 

 of postsmolts in neritic habitats. Coher- 

 ence patterns in the performance of stock 

 complexes has led investigators to search 

 for broad-scale forcing functions to ex- 

 plain variation in returns rate by age (Friedland et 

 al., 1993; Friedland et al., 1998a). In the Northeast 

 Atlantic, a direct link between postsmolt survival and 

 ocean climate has been reported (Friedland et al., 

 1998a). Spring thermal conditions were associated 

 with the survival of North Sea stocks, which argues 

 that the postsmolt nursery in that region was oce- 

 anic and thus directly affected by ocean climate 

 change. However, interpretation of survival signals 

 in the Northwest Atlantic has been complicated by 

 the interplay of mortality and maturation (Friedland 

 et al., 1998b). As the search continues for the factors 

 affecting the survival of Northwest Atlantic 

 postsmolts, investigators must be cognizant of the 

 fact that much of the nursery may occur in inshore 

 neritic waters rather than in pelagic ecosystems and 

 thus may not respond solely to ocean-scale phenom- 

 ena. This situation may be particularly important in 

 evaluating coastal and offshore predators and how 



0.07- 



0.06 



K 0.05 

 0.04- 



0.04 





«*^1 



i+f-H^N^^fc;) 



H 



"T 



"T 



2 4 6 8 10 12 14 16 18 20 22 



Circuli pair 



Figure 5 



Circuli spacing versus circuli pair for Connecticut 2SWiConnl, Penobscot 

 ISW and 2SW (Pen), Saint John ISW and 2SW (SJl, and Gulf of St. 

 Lawrence postsmolts (Gulf) for three sniolt year classes, 1982 (A), 1983 

 (B), and 1984 iC). Error bars mark 9.5'^; confidence intervals. 



they might be impacting salmon populations. For 

 example, a gannet colony may exert predation pres- 

 sure over a substantial part of the northern coast of 

 North America; thus, these and other bird species 

 that are adapted to surface prey, such as Atlantic 

 salmon postsmolts, could cause significant predation 

 (Montevecchi and Myers, 1997). 



The Gulf of St. Lawrence is a large, complex sys- 

 tem that offers a diversity of feeding conditions to 

 smolts upon their entrance into the marine environ- 

 ment. Growth rates would be expected to vary spa- 

 tially in the Gulf owing to, among other things, highly 

 variable thermal conditions over years. Nursery habi- 

 tats within the Gulf appear to provide conditions that 

 would support growth rates comparable to those ob- 

 served in hatchery-reared stocks. But, what clearly 

 differentiates the Gulf habitats from most offshore 

 areas is the rapid continental cooling that occurs in 

 the fall, resulting in an emigration of postsmolts from 



