for catfish and stonecats, which were readily identified, the percentages given 

 for the forage species are probably low due to the large volume of unidentified 

 fish parts. 



Aquatic macroinvertebrates were found mainly in the smaller sauger. 

 Insects, of which Traverella albertana, the only Tvaverella species in the 

 lower Yellowstone, was the most abundant, accounted for 1.7 percent of the 

 food, a low percentage because few small fish were taken. Lengths of sauger 

 ranged from 201 to 546 mi (7.91 to 21.50 in). Sauger containing only insects 

 in their stomachs averaged 246 mm (9.69 in); those which ate only fish averaged 

 300 mm (11.81 in). No sauger over 282 mm (11.10 in) in length contained 

 insects. The evidence suggests that macroinvertebrates are an important food 

 only for young sauger. It is expected that insects form the major portion of 

 the diet in fry and fingerlings. Priegel (1970) found that most of the insects 

 consumed by sauger and walleye in Lake Winnebago, Wisconsin, were taken by 

 fish under 275 mm (10.83 in) in length. In another lake study. Nelson (1968) 

 observed that sauger fry feed on zooplankton and some insects until they attain 

 lengths of 70 to 100 mm (2.76 to 4.33 in). Beyond this length, fish become 

 more important in the diet. Cross (1967) and Brown (1971) state that the 

 food of young sauger is almost entirely aquatic insects. 



BURBOT 



Table 44 shows that 94.0 percent of the volume in burbot stomachs consisted 

 of fish. The major prey species were flathead chub, stonecats, and minnows of 

 the genus Hybognathus. The brassy minnow (h. hankinsoni) , plains minnow 

 (h. plaaitus) and silvery minnow (H. nuchalis) are the only species of 

 Hybognathus present in the lower Yellowstone River (Brown 1971). 



Benthic insects formed 3.0 percent of the food volume of burbot. As 

 with the sauger, insects occur more frequently in the diet of small fish. 

 The smallest burbot captured for this study was 318 mm (12.52 in). Studies by 

 a number of researchers agree that insects and other invertebrates are the 

 dominant foods of first-year burbot (Bailey 1972, Bjorn 1940, Hewson 1955, 

 Lawler 1963, Miller 1970, and Volodin and Ivanova 1969). 



CHANNEL CATFISH 



Aquatic and terrestrial insects were the most abundant food types of the 

 channel catfish (table 45). Mayflies, especially Traverella, and grasshoppers 

 composed a large part of the insect bulk. It was noted that many of the 

 Traverella were emergent adults. Several stomachs contained a large number 

 of small Hymenoptera. Only two fish were found in the stomachs of catfish, 

 one of them a large shorthead redhorse [Ploxostoma macrolepidoUm) which dis- 

 placed 396.0 ml of water. The volume percentages of food types were dis- 

 torted by the presence of the shorthead redhorse; table 45 shows that insects 

 accounted for 25.6 percent of the volume, but, if the sucker were not included, 

 the insect volume would increase to 60.8 percent. 



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