NOTE Fnedland el al Relationship between smoll and postsmolt growth in Salmo solar 



circuli spacing indices from the postsmolt growth 

 zone were larger in magnitude than the index from 

 the freshwater zone. CSFM averaged 0.061 mm 

 (SD = 0.0109) and reflected a threefold increase in 

 circuli spacing between the freshwater and marine 

 zones. CSSM averaged 0.064 mm (SD = 0.0100), 

 reflecting the increased growth occurring within 

 the duration of marine residency'. MZL increased 

 over time from approximately 0.6 mm in early 

 August to 1.2 mm by mid-October. 



The data we examined to test the relation- 

 ship between smolt size and freshwater finishing 

 growth and postsmolt growth indicate an absence 

 of any linkage between the two growth environ- 

 ments. We found no significant relationships be- 

 tween smolt sizes as represented by FZL and ei- 

 ther spring (CSFM) or summer (CSSM) postsmolt 

 growth as represented by the circuli spacing indi- 

 ces. The scatter between CSFM and FZL suggests 

 there were no linear trends for any of the study 

 years (Fig. 2A). None of the three regressions had 

 slopes significantly different from zero (Table 1). 

 There was also an absence of any relationship 

 between CSSM and FZL as evidenced by a similar 

 pattern of scatter for the coordinates (Fig. 2B) and 

 by an absence of significant slopes. 



The relationship was further tested by consid- 

 ering the growth that occurs just prior to smolt 

 migration as an indication of smolt condition at 

 entry into the marine environment. As was the 

 case with the bivariate relationships with FZL, 

 CSLF was not a significant predictor of either 

 CSFM or CSSM (Fig. 3). None of the slopes were 

 significantly different from zero (Table 1). 



Growth in the early and later part of the post- 

 smolt season were correlated. There were signifi- 

 cant positive linear relationships between CSSM 

 and CSFM for all three years (Fig. 4), indicating that 

 the postsmolts began their marine residence with rapid 

 growth and continued to grow at a rapid rate through 

 summer. The slopes of all three regressions were sig- 

 nificantly different from zero (Table 1). 



A time series plot of MZL, plotted by date of capture, 

 shows an increasing trend reflecting the growth that 

 postsmolts experience during early marine residence 

 (Fig. 5). For the same fish, we also plotted FZL by date 

 of capture and found a negative trend over time, indi- 

 cating that FZL decreased during the period (Table 1), 

 which would not be consistent with selective mortality 

 of smolts of smaller initial size. 



Discussion 



Our main findings indicate that marine growth of post- 

 smolt Atlantic salmon sampled from August to October 

 in the Gulf of St. Lawrence was independent of fresh- 

 water growth history. Neither smolt size nor the last 

 freshwater growth period of smolts prior to migration 

 was related to postsmolt growth patterns. Furthermore, 



0,12 



10' 



08- 



0,06  



£■ 0,04. 

 E 



9- 12- 



O 0,10' 



0.08- 



0.06 



04 



1982 

 1983 

 1984 



■1982 

 1983 



•1984 



o -o „-,=•*- 



V^'-.-Jf 



_i_.'-- — qiij ^y^T* , ■• sf-®' - 



B 



* » ° ooo.\s«' ce o ■* O 





0,2 



— I — 

 0,6 



— I — 

 1,0 



0,4 0,6 0.8 1,0 1,2 



Freshwater zone length (mm) 



1,4 



Figure 2 



Relationships between circuli spacing during the early marine 

 period (A) and circuli spacing during the summer marine 

 period (B) and freshwater zone length for Atlantic salmon 

 tSalmo salar) in the Gulf of St. Lawrence. 



Table 1 



Linear associations between scale growth indices and 

 date of capture for Gulf of St. Lawrence Atlantic salmon 

 iSalnw salar) postmolts. FZL = freshwater zone length; 

 CSLF=mean of the last five freshwater intercirculi spac- 

 ings; CSFM=mean spacing of intercirculi spacings 2 

 through 6; CSSM = mean spacing of intercirculi spacings 

 7 through 11; DOC = date of capture. 



Linear 

 associations 



Probability Hg 

 slope = 



Predictor iX) Dependent (7) 1982 1983 1984 



FZL 



FZL 



CSLF 



CSLF 



CSFM 



DOC 



DOC 



Sample size 



CSFM 



CSSM 



CSFM 



CSSM 



CSSM 



FZL 



MZL 



0.53 



0.50 



0.27 



0.33 



<0.01 



<0.01 



<0.01 



374 



0.87 

 0.61 

 0.70 

 0.57 

 <0.01 



158 



0.57 

 0.22 

 0.22 

 0.27 

 <0.01 



55 



