HEALEY: UTIUZATION OF THE NANAIMO RIVER ESTUARY 



length (FL) and 4.2 g (Figure 5). Chinook salmon 

 captured in 1976 were slightly smaller on the av- 

 erage, than those captured in 1975, while those 

 captured in 1977 were the largest of all. Average 

 size of Chinook salmon captured in 1977 increased 

 rapidly 3-4 wk earlier than in 1975 and 1976, in 

 keeping with the apparently earlier downstream 

 run in 1977. The differences in size of chinook 

 salmon captured in the 3 yr were not large, at least 

 early in the sampling, and probably reflected dif- 

 ferences in the timing of migration rather than 

 differences in growth rate. The small change in 

 length and weight of chinook salmon in the es- 

 tuary during March and April probably resulted 

 from continued recruitment of downstream mi- 

 grant fry to the estuary population, while the in- 

 crease in May and June reflected growth of the fish 

 residing in the estuary. Seventy millimeters fork 

 length is apparently the size at which chinook 

 salmon leave the estuary and disperse into the 

 marine environment. No young-of-the-year <70 

 mm were captured away from the estuary. The 

 smallest young-of-the-year captured in area 10 

 were 70-75 mm FL. Weisbart (1968) commented 

 that 70 mm was about the size at which juvenile 



70 



60 



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10- 



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15 25 4 14 24 4 14 24 3 13 23 3 13 23 



MAR APRIL 



MAY 



JUNE 



JULY 



Figure 5. — Average fork length and round weight of juvenile 

 chinook salmon captured on the Nanaimo River estuary in 1975 

 (dots), 1976 (circles), and 1977 (triangles). 



chinook salmon became physiologically capable of 

 tolerating high salinity water. 



The increase in size of chinook salmon on the 

 estuary in June was not representative of their 

 true growth rate, as it was influenced by both the 

 continued immigration of small fish from the river 

 and the emigration of fish reaching 70 mm FL. 

 Recaptured fin clipped fish in 1977, however, pro- 

 vided an estimate of the growth rate of a known 

 group of juveniles. Total mark recaptures sampled 

 for length and weight were 36 left pelvic clips and 

 19 right pelvic clips. Left pelvic clips averaged 44 

 mm and 0.92 g when marked, and five of these 

 recovered 47 and 57 days after marking averaged 

 more than 100 mm and 13 g (Table 5). Right pelvic 

 clips averaged 63 mm and 3.36 g when marked, 

 and increased to more than 100 mm and 13 g after 

 29 days (Table 5). The linear regressions of length 

 or logp weight on days since marking indicated no 

 significant difference in the rate of growth between 

 the two marked groups. The data were, therefore, 

 combined by scaling to length and weight at the 

 day of release and growth rates were calculated for 

 the combined data. Growth in length was 1.32 

 mm/day. Instantaneous daily growth in weight was 

 0.0566, or about 5.8% of body weight/day. 



Estimates of Total Estuary Population 



Although the beach seine samples taken in this 

 study provided an adequate measure of distribu- 

 tion and relative abundance of chinook salmon, 

 they do not permit an estimate of the total number 

 of chinook rearing in the estuary. Mark and recap- 

 ture estimates of abundance in 1977 provided a 

 reference point for comparing catches between 

 years and for comparing the downstream run of fry 

 with the estuary population. Between 18 and 21 

 April 1977, 3,187 fish marked with a left pelvic 

 clip were released at Stations 29-31 of the east 



Table 5. — Size at release and recapture of fin-chpped juvenile 

 chinook salmon in the Nanaimo River estuary in 1977. 



663 



