HOMING MIGRATION OF SOCKEYE SALMON, ONCORHYNCHUS NERKA , 



TO THE ERASER RIVER 



C. Grooti and T. p. Quinn^ 



ABSTRACT 



Adult sockeye salmon, Oncorhynchus nerka, return to the Fraser River via either of two routes: a 

 northern route through Queen Charlotte Strait, Johnstone Strait, and the Strait of Georgia between 

 the mainland and Vancouver Island, and a southern route along the west coast of Vancouver Island 

 and through Juan de Fuca Strait. The proportions of the total run of sockeye salmon using the two 

 routes varies substantially from year to year. Understanding the factors influencing the migratory 

 routes of Fraser River sockeye salmon provides a basis for forecasting the coastal migrations of 

 salmon as they make the transition between oceanic and riverine environments. Our analysis of west 

 coast troll catch and high seas tag-recovery data indicates that the salmon make landfall in different 

 coastal regions from year to year. If the majority of Fraser sockeye approach the coast of Vancouver 

 Island, then most will migrate via the Strait of Juan de Fuca. However, when landfall occurs north 

 of Vancouver Island in the Queen Charlotte Sound area, most homeward migrating Fraser sockeye 

 will travel through Johnstone Strait. Northern diversion rates of Fraser River sockeye salmon for the 

 period 1953-77 were positively correlated with Fraser River discharge. For the period 1978-85 a 

 strong positive correlation was evident with sea surface temperature (SST) along the northwest coast 

 of Vancouver Island (Kains Island lighthouse). We conclude that Fraser River discharge and SST in 

 the vicinity of Kains Island do not guide sockeye salmon in any direct way during their coastal 

 approach, but that they reflect oceanographic conditions that affect salmon migrations directly or 

 indirectly by acting on the feeding distribution, distance, or direction they must travel to reach home. 



The Fraser River in British Columbia, Canada, is 

 among the most important producers of sockeye 

 salmon, Oncorhynchus nerka, in North America. 

 Forty to sixty separate stocks, inhabiting the dif- 

 ferent lakes of its watershed, produce 2 to 20 mil- 

 lion adults yearly (IPSFC 1954-1985). Sockeye 

 salmon from the Fraser River system generally 

 spend 1 year in nursery lakes after emergence 

 and then migrate to sea as smolts. Most spend two 

 winters in the ocean, returning to spawn in their 

 home river as 4-yr-olds. To reach the Fraser River 

 from their ocean feeding grounds they can take 

 either of two routes around Vancouver Island 

 (Fig. 1). From 1953 until 1977, the majority 

 homed via the southern route through the Strait 

 of Juan de Fuca (average 84%, range 65-98%). 

 Since 1978, a larger proportion of sockeye have 

 migrated via the northern route through John- 

 stone Strait (average through Juan de Fuca 

 Strait 56%, range 20-78%) (IPSFC 1954-1986). 



1 Department of Fisheries and Oceans, Fisheries Research 

 Branch, Pacific Biological Station, Nanaimo, British Columbia 

 V9R 5K6, Canada. 



^University of British Columbia, Department of Oceanogra- 

 phy, Vancouver, B.C. V6T 1 Y4, Canada; present address: School 

 of Fisheries WH-10, University of Washington, Seattle, WA 

 98195. 



Manuscript accepted April 1987. 



FISHERY BULLETIN: VOL. 85, NO. 3, 1987. 



In 1958 a relatively high proportion (35%) of 

 Fraser River sockeye salmon returned via the 

 northern route. A large number of fish did not 

 make landfall off the west coast of Vancouver Is- 

 land but rather arrived in the more northerly 

 Queen Charlotte Sound area (Tully et al. 1960) 

 (Fig. 1). This coincided with anomalously high 

 water temperatures off the coast of British Co- 

 lumbia. Tully et al. (1960) and Royal and Tully 

 (1961) suggested that intrusion of warm water 

 from the south in 1958 directed the homing sock- 

 eye salmon northward and closer to the main- 

 land. Moreover, the fish appeared 10 days later in 

 the fishery around Vancouver Island and over a 

 longer period than usual, suggesting that they 

 might have detoured around the area of warm 

 water and made their coastal approach in the 

 cooler nearshore waters. Alternatively, they 

 might have initiated their homeward migration 

 later or from a more distant area than usual. 



Favorite (1961), on the other hand, took the 

 view that the unusual extent of dilute sea water of 

 Fraser River origin offshore from Queen Char- 

 lotte Sound in 1958 determined the location 

 where the migrating sockeye entered coastal 

 water. He assumed that homeward migrating 

 salmon are attracted to dilute seawater contain- 



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