HEALEY: UTILIZATION OF THE NANAIMO RIVER ESTUARY 



river divides into two main channels which cross 

 the intertidal mud flat on the east and west sides. 

 The west channel carries most of the flow, how- 

 ever, and during low river flows in the spring and 

 summer a gi'avel berm blocks the east channel, 

 probably preventing any fish movement down this 

 channel. Holden Creek flows across the delta on 

 the east side and joins the east channel of the river 

 about half way across the intertidal mud flat. 

 Hong Kong Creek and Chase River enter the delta 

 from the west and join the west channel of the 

 river near the upper margin of the mud flat. The 

 mud flat between the two main channels of the 

 river is dissected by numerous small stream chan- 

 nels fed by seepage from the main river channels. 

 The smaller streams contributing to the delta do 

 not support chinook salmon spawning but do sup- 

 port chum and coho salmon. 



Salt marshes at the top of the delta are 

 dominated by black grass, J uncus gerardii. The 

 intertidal area has three floral associations: 

 Fucus-Salicornia in the upper tidal area, Ulva- 

 Enteromorpha in the midtide area, and Zostera- 

 Ulva in the low tide area (Foreman^'). Zostera 

 extends in a band across delta front, and well up 

 the east channel of the river. 



The intertidal area of the delta is used for log 

 storage by local sawmills and a pulp mill. Part of 

 the northwest corner of the estuary has been filled 

 in during development and expansion of the Port 

 of Nanaimo. Intermittent dredging occurs at the 

 delta front to keep the shipping lane into Nanaimo 

 Harbor open. Some dyking has occurred along the 

 southern margin of the delta to create farm land. 

 Further details of physical and biological features 

 of the estuary and adjacent lands are given in Bell 

 and Kallman (see footnote 5). 



Seaward from the intertidal area of the delta a 

 wide variety of habitats provide potential nursery 

 area for juvenile salmon, from sheltered bays and 

 lagoons to exposed rocky or sandy beaches. Many 

 of these habitats were sampled during 1975 and 

 1976 to estimate the extent of utilization of 

 habitats away from the river mouth as nursery 

 areas (Figure 2). Some details of the physical and 

 biological features of the habitats sampled are 

 given by Healy et al. (see footnote 7). Apart from 

 sampling locations 10, 11, and 17, within the 



Nanaimo Harbor area (Figure 2), salinity was 

 usually above 27%ii, while spring and summer 

 temperature ranged 6°-15° C (Healey et al. see 

 footnote 7). 



RESULTS AND DISCUSSION 



Downstream Run of Fry 



Downstream movement of the chinook salmon 

 fry had two peaks in 1975, the first on 19 April and 

 the second 14 days later (Figure 3). Fry were mov- 

 ing in small numbers throughout March, but most 

 movement occurred in April and May. A total of 

 10,876 fry entered the traps between 10 March 

 and 24 May. 



Trapping began on 8 April 1976, and chinook 

 salmon were already moving downstream. One 

 peak occuiTed in the 1976 run, although isolated 

 large catches occurred before and aifter the peak 

 (Figure 3). Only 4,360 fry entered the traps in 

 1976 suggesting that the total run was about half 

 that in 1975. 



Downstream migrants averaged 38.3 mm long 

 (0.57 g) and ranged 33-45 mm long (0.33-1.02 gl. 

 Many of the fry still had visible yolk. 



River discharge during the the fry run in 1975 

 ranged 16-100 m^/s, and increases in fry run were 

 generally associated with increases in discharge. 



1976 



"Foreman, R. E. 1975. Nanaimo River estuary mac- 

 rophyte study: Seasonal aspects of macrophyte distribution and 

 standing crop on the Nanaimo River estuary mudflats. BERP 

 Rep. 75-3, final report on Fish. Mar. Serv. Contract OSU4-0217 

 prepared by R. E. Foreman. Botany Dep., Univ. B.C., 41 p. 



Figure 3.— The trap catch of chinook salmon fry (upper panels), 

 river discharge (solid line lower panels), and weekly average 

 river temperature (circles, lower panels) in 1975 and 1976 in the 

 Nanaimo River. Trap catch and discharge are averaged at 2-day 

 intervals for ease of plotting. 



657 



