HEALEY: UTILIZATION OF THE NANAIMO RIVER ESTUARY 



ure 6). The yearling smolts dominate samples 

 taken in late May and early June, after which they 

 disappear and are replaced by young-of-the-year, 

 presumably from the Nanaimo River. This se- 

 quence of events in which 1+ ocean fish are re- 

 placed by 1 -I- stream fish which in turn are replaced 

 by 0-1- ocean fish is not unique to the Nanaimo area 

 but appears to be typical for the Gulf Islands region 

 as a whole (Healey"'). 



Food Habits and Feeding Rates 



A growth rate in excess of 5'7f body weight/day 

 implies good feeding conditions in the estuary 

 (e.g., LeBrasseur 1969). Diets of juvenile chinook 

 salmon were similar in 1976 and 1977, and five 

 taxonomic groups made up the bulk of the diet in 

 the estuary. Harpacticoid copepods were impor- 

 tant in March and early April, decapod larvae and 

 amphipods in April and May, and mysids and in- 

 sect larvae in May-July. Off the intertidal area of 

 the estuary fish larvae, chiefly herring, dominated 

 the diet of juvenile chinook salmon from May 

 through August, while calanoid copepods, decapod 

 larvae, and insects were occasionally important. A 

 shift from a predominantly invertebrate diet to a 

 predominantly fish diet, therefore, occurred as the 

 young chinook salmon dispersed away from the 

 intertidal area of the estuary. 



Average weights of stomach contents varied 

 considerably from sample to sample; nevertheless, 

 some generalizations appear possible. Weights of 

 stomach contents of juvenile chinook salmon cap- 

 tured on the estuary in 1975 ranged about 3-5'5f of 

 body weight in April but dropped rapidly to a low 

 of about O.lVf of body weight as the chinook salm- 

 on population on the estuary increased in May 

 (Table 7). Weights of stomach contents of juveniles 

 on the estuary were uniformly low in 1976, never 

 rising above 2.V7< of body weight (Table 7). 

 Stomach contents of juveniles captured in 1977 

 ranged 2-Wi of body weight except during the 

 peak of fry abundance when contents dropped to 

 0.5% of body weight (Table 7). Assuming that 

 stomach contents are a reflection of feeding condi- 

 tions, it appears that feeding conditions were 

 poorest in 1976, better in 1977, and possibly best of 

 all in 1975 when the population was greatest. 

 Peak population densities were associated with a 

 decline in stomach contents, and by inference, a 



Table 7. — Stomach contents as a percent of body weight for 

 juvenile chinook salmon captured in the intertidal area of the 

 Nanaimo River estuary and off the intertidal area 1975-77. 

 Sampling week dates are for 1976. Add 2 days for 1975 and 

 subtract 1 day for 1977 to get the correct starting date for those 

 years. 



'^Healey. M. C, 1978. The distribution, abundance and 

 feeding habits of juvenile Pacific salmon in Georgia Strait, 

 British Columbia. Fish. Mar. Serv. Tech. Rep. 788, 49 p. 



decline in food intake in the years of good feeding 

 conditions. 



Weights of stomach contents of juvenile chinook 

 salmon captured away from the intertidal area of 

 the estuary were similar to those in the estuary 

 during May and early June, but in mid-June 

 dropped below those from the estuary. Weights of 

 stomach contents of chinook salmon captured 

 offshore were lower in 1976 than in 1977, as was 

 observed for the estuary population (Table 7). 



The composition of the diet of juvenile chinook 

 salmon in the Nanaimo estuary was similar to 

 that reported by Sibert and Obrebskii 1976) for the 

 Nanaimo estuary in 197.3 and to that recorded by 

 Dunford ( 1975) in similar habitats on the Fraser 

 estuary. The relative timing and importance of 

 specific items in the diet was different than in the 

 Fraser, but this probably reflects differences in 

 abundance of the different diet items and the op- 

 portunistic feeding behavior of the fish. The 

 change in diet of juvenile chinook salmon from 

 invertebrates while in the intertidal area of the 

 Nanaimo estuary, to larval fish when away from 

 the intertidal area was consistent with observa- 

 tions on the Fraser estuary. Juveniles in the 

 Fraser River and marsh area fed mainly on inver- 

 tebrates, but those on Roberts and Sturgeon 

 Banks fed mainly on juvenile herring (Goodman 

 see footnote 2). 



667 



