FISHERY BULLETIN: VOL. 85, NO. 3 



coupled with an independent sense of direction. 

 Moreover, as the salmon near the coast, they may 

 experience a decrease in temperature (Table 3). 

 We conclude that the relationship between sea 

 surface temperatures at Kains Island and the di- 

 version rate of sockeye salmon returning to the 

 Fraser River via Johnstone Strait between 1978 

 and 1985 reflects the influence of ocean condi- 

 tions on the behavior offish, either on the feeding 

 distribution prior to homing (see also Mysak 

 1986) or on the homing migration itself. 



Fraser River Discharge and 

 Sockeye Salmon Migration 



Most of the fresh water along the British Co- 

 lumbia coast originates from the Columbia, 

 Fraser, and Skeena Rivers and distinct tongues of 

 dilute water (SSS of 32.6%c and less) extend sea- 

 ward from the Strait of Juan de Fuca and Queen 

 Charlotte Sound several hundred kilometers off- 



shore (Favorite 1961). Wickett (1977) suggested 

 that it was the Fraser River water discharged in 

 the ocean to the northwest of Vancouver Island 

 that increased the percentage of Fraser River 

 sockeye migrating through Johnstone Strait. 



Fraser River sockeye migrating from their 

 ocean feeding grounds towards the British Co- 

 lumbia coast pass through the areas of dilute sur- 

 face water ("dilute domain") long before making 

 landfall (Fig. 9). Interannual changes in river dis- 

 charge and the resulting dilute extensions off- 

 shore could affect the coastal approach routes of 

 Fraser River sockeye by causing more northerly 

 landfall than usual during years of high levels of 

 runoff (Favorite 1961; Wickett 1977). 



What might be the mechanism that underlies a 

 direct relationship between river discharge and 

 migration route of adult Fraser River sockeye 

 salmon? Two possibilities present themselves. 

 First, returning sockeye salmon could prefer 

 lower salinity water as they home, similar but 



64°N 



I30°W 



Figure 9. — The estimated distribution of maturing Fraser River sockeye salmon in June, July, and August in relation to regions of 



dilute water and upwelling. 



466 



