HEALEY: UTILIZATION OF THE NANAIMO RIVER ESTUARY 



Table 2. — Trap catch, estimate of marks migrating downstream, recaptures in the traps, and estimated daily run of 

 chinook fry in the Nanaimo River in 1975. Population estimates in italics were derived from trap catch divided by average 

 trap efficiency (0.0175). All other estimates are Peterson type estimates. 



for .37 days of the 1975 run and ranged 40-133,986 

 fish/day. The sum of these estimates was 687,568 

 chinook salmon, and total trap catch for the days 

 when estimates were made was 9,188. The ratio of 

 catch to total run for the Peterson estimates was 

 0.013, indicating only 1.3^^ trap efficiency. This 

 estimate was strongly influenced, however, by the 

 large population estimate for 3 May, which re- 

 sulted from a large catch in which there were few 

 recaptures (Table 2). Ignoring this estimate, the 

 ratio of trap catch to Peterson population esti- 

 mates was 0.0151, closer to the average efficiency 

 based on mark recaptures. 



Population estimates for all days of the run to- 

 taled 784,155 in 1975. Assuming trap efficiency 

 was similar in 1976, the run was about 300,000 

 during the trapping period. 



Although most chinook salmon are expected to 

 go to sea after about 2 mo of residence in their 

 natal stream, downstream movement of fry 

 shortly after emergence has been observed in 

 other systems. In the Big Qualicum River, 100 km 

 north of the Nanaimo, between 3,000 and 241,000 



fry migi'ated downstream mainly in March and 

 April from 1961 to 1965, although the time ol 

 greatest movement varied from late March to 

 early May (Lister and Walker 1966; Lister and 

 Genoe 1970). The fry migration was followed by a 

 fingerling migration in June which was usually 

 larger than the fry migration. In the Cowichan 

 River, 50 km south of the Nanaimo River, a large 

 downstream movement of fry was recorded during 

 March and April in 1966 and 1967 followed by a 

 smaller fingerling movement in June (Lister et 

 al.'^). The survival of these fry and their contribu- 

 tion to the adult population were unknown, but 

 presumed to be slight (Lister and Walker 1966). 

 The number of chinook salmon fry, estimated 

 to have migrated downstream in the Nanaimo 

 River in 1975 and 1976, was 5-10 times greater 

 than in the Big Qualicum River which has a simi- 

 lar escapement (Lister and Walker 1966). This 



'^Lister, D, B,,C. E.Walker, and M.A.Giles. 1971. Cow- 

 ichan River chinook salmon escapement and juvenile production 

 1965-1967 Can. Dep. Fish. For. Tech. Rep. 1971-3, 48 p. 



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