BECKER: PARAMETERS OF JUVENILE CHINOOK SALMON 



50 60 70 



LEriGTH IN mm (X) 



Figure 8. — Length-weight relationship of juvenile chinook 

 salmon in the central Columbia River, March-July 1969. 



various size groups, included in Table 5, show 

 that the ratio of stomach food biomass to fish 

 weight generally increases as the fish become 

 larger. The FI value was low for the eight 

 fish in the largest size group (76-85 mm) 

 collected in late July. 



DISCUSSION 



Food Organisms 



Distinctive features of feeding activity for 

 juvenile chinook salmon in the central Columbia 

 River appear to be fourfold: first, the fish 

 utilize relatively few insect groups, predomi- 

 nantly Chironomidae; second, they depend 



largely upon autochthonous river organisms; 

 third, they select prey drifting, floating, or 

 swimming in the water; and fourth, they are 

 apparently habitat opportunists to a large 

 extent. These features are not necessarily 

 unique among young salmonids in lotic en- 

 vironments. Here, in the free-flowing Columbia 

 River, they demonstrate a close relationship 

 with existing stream conditions. 



Chironomids are of variable importance to the 

 diet of juvenile chinook salmon in other streams. 

 An early study conducted in the Sacramento 

 River indicated that young chinook salmon 

 consumed midges only to a limited extent, 

 although floating and drifting insects did form 

 the greatest portion of their diet (Rutter, 

 1904). Young chinook salmon in tributaries 

 of the central Columbia River above Hanford 

 in 1938 utilized few, if any, midges, although 

 the fish fed almost exclusively on insects and 

 the order Diptera was of greatest numerical 

 importance (Chapman and Quistorff, 1938); 

 these fish were relatively large, up to 152 mm, 

 and were probably young spring chinook sal- 

 mon. The food of juvenile chinook salmon 

 in the middle Willamette River in 1958 was 

 39% Diptera, primarily midges, and 40% Ephem- 

 eroptera (Breuser, 1954). Emigrating chinook 

 salmon in the lower Sacramento-San Joaquin 

 system consumed primarily insects (90% ) in 

 1964 but only 16% were midges (Sasaki, 1966). 

 Adult and immature midges were a major 

 dietary item of juvenile chinook salmon in 

 the lower Chehalis River, along with other 

 Diptera, Trichoptera, Plecoptera, and Ephem- 

 eroptera, in 1965 (Herrmann, 1970). 



Published records reveal that insects domi- 

 nate the food of other species of juvenile 



Table 5. — Mean length, mean weight, coefficient of condition (K) and feeding 

 intensity (FI) for 10-mm size groups of juvenile chinook salmon in the central 

 Columbia River, March-June 1969. 



The few fish under 36 and over 85 mm in fork length were omitted. 



397 



