Table 3. 



FISHERY BULLETIN: VOL. 81, NO. 4 



-Total length (mm) characteristics of subyearling chinook salmon and commonly associated species captured in four habitats of the 



Columbia River estuary in 1980. N = total number captured. 



shorter, or no longer than, subyearling chinook 

 salmon. 



About 5,000 stomachs from 50 species of fish 

 collected from February through October 1980 were 

 analyzed. There were only two predations on juvenile 

 salmonids — two yearling chinook salmon each ate a 

 subyearling chinook salmon. Juvenile subyearling 

 chinook salmon preyed on nonsalmonid fish, chiefly 

 in the lower estuary. Nonsalmonid fish consumed by 

 subyearlings included Pacific sand lance, Am- 

 modytes hexaptcrus; northern anchovy; longfin smelt, 

 Spirinchus tholeichthys; and whitebait smelt, Allos- 

 merus elongatus. Principal prey items accounted for 

 an average of 93 1 7< of the diet biomass for all fish 

 species with a range of 53- 1007c . Principal prey items 

 of juvenile salmonids and commonly associated non- 

 salmonids were invertebrates, chiefly crustaceans 

 (Figs. 3, 4); fish were eaten but they were never the 

 only prey. 



Figures 5 and 6 show the degree of diet overlap be- 

 tween salmonids and commonly associated species. 

 In the pelagic areas during spring, all the salmonids 

 except steelhead (upper pelagic) had significant diet 

 overlap values (>0.6). Salmonid species had signifi- 

 cant diet overlap values with American shad in the 

 lower estuary and threespine stickleback in the up- 



per estuary. In the intertidal areas during spring, 

 significant diet overlap occurred only between sub- 

 yearling chinook salmon and starry flounder. Signifi- 

 cant diet overlap in the spring was primarily due to 

 the importance of Corophium salmonis and C. 

 spinicorne as prey items. In summer there was no 

 significant fish diet overlap. 



On 18 May 1980, Mount St. Helens erupted and 

 deposited large amounts of volcanic ash and 

 sediments into the Columbia River, thereby increas- 

 ing the turbidity of the estuary. For a short time, the 

 increased sediment loads and high turbidities 

 reduced the amount and variety of food items eaten. 

 By July 1980, turbidities returned to lower levels. 



DISCUSSION 



Some of the same species associated with juvenile 

 chinook salmon in the Columbia River estuary were 

 found in similar associations in other Pacific 

 Northwest estuaries. Conley (1977), working in 

 Everett Bay in Puget Sound, Wash., caught many 

 shiner perch, Cymatogaster aggregata; Pacific stag- 

 horn sculpin, Leptocottus armatus; and starry floun- 

 der in intertidal areas along with juvenile chinook 

 salmon. Myers (1980), working in Yaquina Bay, 



820 



