INTERRELATIONSHIPS BETWEEN JUVENILE SALMONIDS AND 

 NONSALMONID FISH IN THE COLUMBIA RIVER ESTUARY 



George T. McCabe, Jr., William D. Muir, Robert L. Emmett, and Joseph T. Durkin 1 



ABSTRACT 



Interrelationships between juvenile salmonids — coho salmon, Oncorhynchus kisutch; chinook salmon, 0. 

 tshawytscha; and steelhead, Salmo gairdneri — and nonsalmonid fish were studied in the Columbia River es- 

 tuary during 1980. Nonsalmonid species were numerically dominant in pelagic and intertidal areas of the 

 lower estuary. In pelagic and intertidal areas of the upper estuary, juvenile salmonids, particularly subyear- 

 ling chinook salmon were proportionally important. Nonsalmonid species commonly associated with 

 juvenile subyearling chinook salmon included American shad, Alosa sapidissima; Pacific herring, Clupea 

 harengus pallasi; northern anchovy. Engraulis mordax; surf smelt, Hypomesus pretiosus; longfin smelt, 

 Spirinchus thaleichthys; peamouth, Mylocheilus caurinus; threespine stickleback, Gasterosteus aculeatus; 

 shiner perch, Cymatogaster aggrcgata; Pacific staghorn sculpin, Leptocottus armatus; and starry flounder, 

 Platichthys stellatus. Commonly associated species were generally defined only in reference to subyearling 

 chinook salmon because, of all the juvenile salmonids, subyearling chinook salmon were clearly the most 

 abundant and available in sizable numbers for the longest time. Predation on juvenile salmonids by non- 

 salmonids and other juvenile salmonids was insignificant. Significant diet overlap occurred among subyearling 

 and yearling chinook salmon, coho salmon, and steelhead during the spring. American shad, threespine 

 stickleback, and starry flounder had significant diet overlaps with juvenile salmonids. 



The Columbia River system is an important pro- 

 ducer of Pacific salmon {Oncorhynchus spp.) and 

 steelhead, Salmo gairdneri, in North America 

 (Chaney and Perry 1976; Bohn and Stockley 1981). 

 Salmonids (wild and hatchery) originating from the 

 Columbia River system provide fish for both river 

 and ocean fisheries (recreational and commercial). 

 Historically, the world's largest migration of adult 

 chinook salmon, 0. tshawytscha, occurred in the 

 Columbia River (Van Hyning 1973). Dam construc- 

 tion, poor logging and agricultural practices, over- 

 fishing, and pollution have severely reduced adult 

 salmonid returns to the Columbia River system. Ef- 

 forts to improve the runs, such as large hatchery 

 releases of juveniles, collection and transportation of 

 juveniles at selected dams, and the installation of 

 dam spillway deflectors to reduce nitrogen super- 

 saturation have enhanced adult returns, but failed to 

 increase them to historical levels. There is concern by 

 some resource managers that significant losses of 

 juvenile salmonids may be occurring in the ocean 

 and/or estuary. They feel these losses may be due to 

 predation or competition for the same food or- 

 ganisms by nonsalmonid fish. 



No published information is known to exist on the 

 interrelationships between juvenile salmonids and 



'Northwest and Alaska Fisheries Center, National Marine 

 Fisheries Service, NOAA, 2725 Montlake Boulevard East, Seattle, 

 WA 98112. 



nonsalmonid fish throughout the Columbia River es- 

 tuary; this paper helps fill that void. Our objectives 

 were to document the following: 1) The proportional 

 abundance of salmonids and nonsalmonids in 

 various estuarine habitats, 2) the nonsalmonid fish 

 species associated with juvenile salmonids, 3) the 

 length characteristics of nonsalmonids and juvenile 

 salmonids, 4) predation on salmonids, and 5) prey 

 consumption and possible competition between 

 salmonids and nonsalmonids in similar habitats. 



METHODS AND MATERIALS 

 Study Area 



The study was carried out in the Columbia River es- 

 tuary between River Kilometers 3 and 62 (Fig. 1). 

 The estuary is a drowned river mouth with delta 

 islands in the upper portion. Salinity intrusion in the 

 estuary fluctuates considerably because of changing 

 river flows and tide conditions. Vertical salinity 

 gradients exist in parts of the estuary, with the 

 highest salinities in deep water near the bottom (Neal 

 1972; McConnell et al. 1981). 



We divided the estuary into upper and lower areas 

 (Fig. 1); these two areas were further divided into 

 pelagic and intertidal habitats. Pelagic and intertidal 

 areas of the upper estuary were classified as 

 freshwater. The lower estuary was classified as a mixed 

 zone, with salinities ranging from to 33%o depend- 



Manuscript accepted Mav 1983. 



FISHERY P'LLETIN: VOL. 81, NO. 4. 1983. 



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