BEAC'HAM and STARR: POPULATION BIOLOGY OF CHUM SALMON 



50 100 150 200 250 300 350 400 450 500 



Number of pink and chum fry 1 .10 ) 



I 3 5 7 9 II 13 15 17 19 21 23 25 27 29 I 3 5 

 April Moy 



Figure 7.— Fry-to-adult survival for chum salmon versus total 

 abundance of pink and chum salmon fry. The abundance of 

 pink fry from even-numbered brood years was assumed to be 

 negligible. 



brood years may be accounted for by the early 

 downstream migration, and the same condition 

 may apply to even brood years (Fig. 8). 



With fry-to-adult survivals of Fraser River 

 chum salmon generally lower in odd brood years 

 than in even ones, odd- and even-numbered brood 

 years were separated in a further analysis of var- 

 iability in the returns to spawners relationship. 

 The R/S ratio for even brood years was inversely 

 related with the total number of returning adults 

 of the previous odd brood year (Fig. 9). This rela- 

 tionship was determined through regression and 

 is described by: 



Figure 8.— Fry-to-adult survival of chum salmon versus medi- 

 an date of downstream migration. 



^ = 1.367 + 

 St 



0.3867 



R 



(n = 7) 



(9) 



«-i 



where R t = total returns for even-numbered 

 brood year 

 S t = spawning escapement producing 

 that brood year 

 R t -i = total returns of previous brood 

 year in millions 



and the correlation between R t /S, and \/R,. x was 

 significant (r = 0.91, P<0.01). This equation can 

 be rearranged to give a prediction of total num- 

 ber of returning adults in year t, given escape- 

 ment and total return of the previous brood year. 

 The above suggests that survival of chum salmon 

 in the marine environment is dependent upon the 

 abundance of conspecifics in the previous brood 

 year. Marine survival may thus be density-de- 



2 4 6 8 10 12 14 16 



Returns of previous broodyeor ( x I ) 



Figure 9.— Ratio of returns/spawners for even-numbered 

 brood years of Fraser River chum versus chum abundance in 

 previous brood year. 



pendent, and interbrood year interactions, pos- 

 sibly through competition for food, may affect 

 marine survival of chum. 



Pink salmon have been implicated in the pres- 

 ent study as impacting population dynamics of 

 Fraser River chum salmon during odd brood 



821 



