FISHERY BULLETIN: VOL. 80, NO. 4 



Marc h 



Apr i 



May 



Figure 3.— Mean time of chum fry downstream migrations on 

 theFraser River, 1965-80. Dotted lines indicate 95% confi- 

 dence limits. 



measured as the days from April 1 to the date of 

 50% migration. Abbotsford airport is located 

 near many major chum salmon spawning areas 

 (Fig. 1). The model fitted was: 



25.53 



r : _ n „. (n 



rrd 



.444 



15) 



T = 



R = 



E = 



mean monthly air temperature at 

 Abbotsford airport from Decem- 

 ber through February 



total rainfall in cm at Abbotsford 

 airport from November through 

 January 



number of eggs deposited X10 6 . 



(2) 



The regression was significant (R 2 = 0.77, F = 

 10.75, df = 4 and 13, P<0.01), and the correlation 

 matrix for the model is shown in Table 5. The in- 

 dividual factors of rainfall (r = —0.28) and egg 

 numbers (r = —0.005) were not significantly cor- 

 related with egg survival, but their interactions 

 with temperature were. Egg survival tended to 

 increase during drier winters, but if these drier 

 winters were also relatively cold, then egg survi- 

 val was lowered. If the winter was both relatively 

 dry and warm, then egg survival was good, as 

 was the case for the 1976 brood year (Table 4). 



and the regression was significant (r = 0.61, 

 P<0.05) (Fig. 4). Fry tend to migrate down- 

 stream earlier following a warmer winter than 

 following a colder winter, presumably because 

 warmer temperatures accelerate egg develop- 

 ment. 



Based on estimates of the number of migrating 

 fry and egg deposition (Table 4), egg-to-fry sur- 

 vival varied from 6% to about 35% in the 1961-78 

 brood years. Multiple regression was used to de- 

 termine the relationship of rainfall, egg num- 

 bers, air temperature, and their interactions on 

 variability in egg survival. The model fitted 

 through stepwise regression was: 



S=aT+bTX— + c TX — + d T 



R E 



1 1 

 X — X — + e 

 R E 



where S = % egg to fry survival 

 818 



(3) 



28 



o 12 



12 3 4 



Mean monthly temperature (Dec- Feb.) (°C) 



Figure 4.— Median date of downstream chum fry migration 

 versus mean monthly temperature from December through 

 February as measured at the Abbotsford airport. 



