FISHERY BULLETIN: VOL. 77, NO, 3 



Seasonal changes in the diet of chinook sahnon 

 in the intertidal area of the estuary indicated that 

 a combination of size selection and availability 

 influenced the diet. Very small organisms (har- 

 pacticoids and cladocerans) occurred in stomachs 

 only in the early spring when the fish were 50 mm 

 or less in length. Larger organisms (amphipods. 

 mysids) were important later in the season when 

 the fish were considerably larger. Insects were 

 important diet items throughout, presumably be- 

 cause of their widespread availability in the 

 habitats sampled. 



CONCLUSIONS 



The Nanaimo River population of juvenile 

 chinook salmon is composed offish which go to sea 

 in their first year and fish which remain in 

 freshwater for 1 yr, with those which go to sea in 

 their first year most numerous. Chinook salmon 

 which migrate to sea in their first year are the 

 most common life history type in British Colum- 

 bia (Milne'^; Godfrey see footnote 13). In the 

 Nanaimo River many of those chinook salmon 

 which go to sea as young-of-the-year move 

 downstream as recently emerged fi^y and rear to 

 smolt size in the intermediate salinity of the es- 

 tuary. Large numbers of chinook salmon fry are 

 found in the marshes of the Fraser estuary in 

 spring and summer (Dunford 1975) and in the 

 estuaries of other rivers in which chinook salmon 

 spawn (Healey unpubl. data). Estuaries, there- 

 fore, are important nursery areas for chinook 

 salmon, a fact which has not hitherto been ap- 

 preciated. 



ACKNOWLEDGMENTS 



Technical staff who contributed to the collection 

 and analysis of data presented include R.V. 

 Schmidt, F. P. Jordan, and R. M. Hungar. Fry trap- 

 ping was performed by R. Wilson under contract. 

 Robin Le Brasseur and T. G. Northcote criticized a 

 draft of the manuscript. 



LITERATURE CITED 



Brett, J, R. 



1952. Temperature tolerance in young Pacific salmon. 



"Milne, D. J, 1964. Sizes and ages of chinook (Oncorftvn- 

 ckus tshawytscha) and echo (O. kisutch^ salmon in the British 

 Columbia troll fisheries 1 1951-19591 and the Fraser River gillnet 

 fisheries (1956-1959). Fish. Res. Board Can. Manuscr. Rep. 

 776, 36 p. 



genus Oncorhynchus. J Fish Res, Board Can, 9:265- 



323. 

 DlNFORD, W, E, 



1975. Space and food utilization by salmonids in marsh 



habitats of the Fraser River estuary. M, Thesis, Univ, 



British Columbia. 81 p 

 HlWTER. J, G. 



1959. Survival and production of pink and chum salmon in 



a coastal stream J, Fish. Res. Board Can, 16:835-886, 

 LkBk,\s,ski'R, R, J 



1969, Growth of juvenile chum salmon [Oncorhynchus 

 keta) under different feeding regimes, J, Fish, Res, 

 Board Can, 26:1631-1645, 



LISTER, D. B., .\s\) H S GKXDE 



1970, Stream habitat utilization by cohabiting underyear- 

 lings of chinook {Oncorhynchus tshauytscha ) and coho lO, 

 kisutch I salmon in the Big Qualicum River, British Colum- 

 bia, J, Fish, Res, Board Can, 27:1215-1224, 



LISTER, D. B,, R, A, L, H,-\RVEV, ,\.\D C, E, W.ALKER, 



1969. A modified wolf trap for downstream migrant young 

 fish enumeration. Can. Fish Cult. 40:57-60. 

 LISTER. D, B,, AND C, E, WALKER, 



1966, The effect of flow control on freshwater survival of 

 chum, coho and chinook salmon in the Big Qualicum 

 River, Can. Fish Cult, 37:3-25. 



MclNERNEY, J. E. 



1964, Salinity preference: an orientation mechanism in 

 salmon migration, J, Fish Res, Board Can, 21:995-1018, 



MEHAN, W, R,, AND D, B, SiNIFF, 



1962, A study of the downstream migrations of anadro- 

 mous fishes in the Taku River, Alaska, Trans, Am, 

 Fish, Soc, 91:399-407. 



Parker, R. R. 



1963, Effects of formalin on length and weight of 

 fishes, J, Fish, Res, Board Can, 20:1441-1455, 



REIMERS, P, E, 



1971, The length of residence of juvenile fall chinook salm- 

 on in Sixes River, Oregon, Fish Comm, Oreg, Res, 

 Briefs, 99 p, 



REIMERS, P, E,, AND R, E, LOEFFEL, 



1967, The length of residence of juvenile fall chinook 

 salmon in selected Columbia River tributaries. Fish 

 Comm, Oreg, Res, Briefs 13:5-19. 



RICKER, W. E, 



1975, Computation and interpretation of biological statis- 

 tics of fish populations. Fish, Res, Board Can, Bull, 191, 

 382 p, 



SIBERT, J,, AND S, OBREBSKI 



1976, Frequency distributions of food item counts in indi- 

 vidual fish stomachs. In C, Simenstad and S, Lipovsky 

 leditorsl. Fish food habits studies, 1st Pacific Northwest 

 Technical Workshop Proceedings, p, 107-114, 

 Washington Sea Grant, Univ, Wash,, Seattle, 



STEIN, R. A., P, E, REIMERS, ANTJ J D, HALL, 



1972, Social interaction between juvenile coho (Oncor/ivn- 

 chus kisutch ) and fall chinook salmon (O, tshawytscha) in 

 Sixes River, Oregon, J, Fish, Res, Board Can, 29:1737- 

 1748, 



WEISBART, M. 



1968, Osmotic and ionic regulation in embryos, alevins, 

 and fry of the five species of Pacific salmon, Ctm, J, Zool, 

 46:385-397, 



668 



