UTILIZATION OF THE NANAIMO RIVER ESTUARY BY 

 JUVENILE CHINOOK SALMON, ONCORHYNCHUS TSHAWYTSCHA 



M. C. Healey' 



ABSTRACT 



Chinook salmon are considered, normally, to spend from a few months to a year rearing in freshwater 

 before migrating to sea. Although large downstream movement of fry, recently emerged from spawn- 

 ing gravels, has been observed in several river systems, it has been suggested that most of these 

 migrant fry are lost to the population. This report describes the fate of downstream migrant chinook 

 salmon fry in the Nanaimo River, British Columbia. In 1975 and 1976 most of the potential fry 

 production from the river system was estimated to have passed by a trapping location near the river 

 mouth. Many of these fry were subsequently found rearing in the intertidal area at the river mouth 

 where salinity was commonly above 20%o. Very few chinook salmon fry were captured at other 

 sampling sites within a 10 km radius of the river mouth. Juvenile chinook salmon were present in the 

 intertidal area of the estuary from March to July each year, but peak numbers occurred in April and 

 May. Peak estuary population was estimated to be 40.000-50,000 in 1975 and 20.000-25,000 in both 

 1976 and 1977. While in the estuary, chinook salmon grew about 1.32 mm per day or 5. 8'7r of their body 

 weight per day. Individual fish probably spent an average of about 25 days rearing in the estuary and 

 left the estuary when about 70 mm fork length. While in the estuary, juvenile chinook salmon fed on 

 harpacticoid copepods, amphipods, insect larvae, decapod larvae, and mysids. After leaving the es- 

 tuary, they fed mainly on juvenile herring. The stomach content of chinook salmon captured in the 

 estuary averaged 5% of body weight or less, and varied seasonally and between years. It appears that in 

 the Nanaimo and probably in other systems with well-developed estuaries, that the estuary is an 

 important nursery for chinook salmon fry. 



After they emerge from the spawning gravel in 

 early spring, chinook salmon, Oncorhynchus 

 tshawytscha, are considered, normally, to spend 

 from a few months to a year in freshwater before 

 migrating to sea (Reimers and Loeffel 1967; Stein 

 et al. 1972; Mehan and Siniff 1962; Lister and 

 Walker 1966). Recently, Reimers (1971) and Dun- 

 ford (1975) showed that juvenile chinook salmon 

 may also spend considerable time rearing in es- 

 tuaries after their downstream migration and be- 

 fore moving into high salinity water. Although 

 juvenile chinook salmon are known to occur in a 

 number of British Columbia estuaries ( Goodman^; 

 Hoos and Vold^; Bell and Kallmann Bell and 



'Department of Fisheries and Oceans, Resource Services 

 Branch, Pacific Biological Station Nanaimo, B.C., Canada V9R 

 5K6. 



^Goodman, D. 1975. A synthesis of the impacts of the pro- 

 posed expansion of the VIA. and other developments on the 

 fisheries resources of the Fraser River estuary. Unpubl. man- 

 user., 137 p. -(- append. Environ. Can., Fish. Mar. Serv., Van- 

 couver 



'Hooe, L. M., and C. L. Void. 1975. The Squamish River 

 estuary: Status of environmental knowledge to 1974. Environ. 

 Can., Fish. Mar. Serv. Spec. Estuary Ser. 2, 361 p. 



'Bell, L. M., and R. J. Kallman. 1976. The Cowichan- 

 Chemainus River estuaries: Status of environmental knowledge 

 to 1975. Environ. Can., Fish. Mar. Serv. Spec. Estuary Ser. 4, 

 328 p. 



Kallman^), the importance of estuarine habitats as 

 nursery areas for young chinook salmon is not well 

 documented. The purpose of this report is to pre- 

 sent information on the utilization of the Nanaimo 

 River estuary and adjacent marine areas by 

 juvenile chinook salmon and to consider the im- 

 portance of the estuary to the stock. Specifically, I 

 shall discuss the timing of downstream movement 

 and abundance of chinook salmon fry in the river; 

 their distribution, abundance, and length of resi- 

 dence in the estuary and in marine waters adja- 

 cent to the estuary; and their growth rate and food 

 habits. In this report the term "fry" refers to 

 juvenile chinook salmon that recently emerged 

 from the spawning gravel, often still with exter- 

 nally visible yolk. 



METHODS 



River Sampling 



Downstream migrating chinook salmon fry 

 were captured in seven inclined plane fry traps 



Manuscript accepted March 1979 



FISHERY BULLETIN: VOL. 77, NO. 3, 1980 



^Bell.L.M., and R.J. Kallman. 1976. The Nanaimo River 

 estuary: Status of environmental knowledge to 1976. Environ. 

 Can., Fish. Mar. Serv. Spec. Estuary Ser. 5, 298 p. 



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