FISHES OF DOUGLAS LAKE, MICHIGAN. 235 



the thermocline. In this it agrees with the pike, the perch, and the sucker. It may go 

 deeper at other seasons of the year, as the sucker appears to do. 



Six of the specimens in our table contained food, and we have records of two others. 

 Of these eight, six had eaten crayfish with or without other food; four had eaten only 

 crayfish; one had eaten crayfish in addition to a fish; one, crayfish in addition to fish 

 and a leopard frog. The seventh had eaten a leopard frog only. The eighth contained 

 numerous specimens of the large cladoceran, Leptodora hyalina. These last could not be 

 examined with the lens, but the naked eye left practically no doubt as to their identity. 

 With the exception of no. 6, the fish whose stomachs contained either frogs or fish (no. 

 9 and 11) had been taken on hooks baited with these but not with crayfish. If we 

 exclude the frogs and fish in no. 9 and 1 1 , there remain seven small-mouthed bass, six of 

 which had eaten crayfish, accompanied in one case by fish, while one had eaten only 

 Leptodora. The crayfish were not identified, but that found in the bass taken at 45 feet 

 was probably Cambarus mrilis, which has been several times brought up in the gill net 

 from that depth, and is the only species known to occur there. There can be no 

 doubt that in midsummer the crayfish is the chief constituent of the food of the small- 

 mouthed bass in Douglas Lake. Forbes and Richardson (1908) call attention to the fact 

 that little is known of the food of this species. They examined the stomachs of three 

 individuals and found their contents to consist "wholly of fishes and crayfishes, 

 approximately a third of the first and two-thirds of the second." 



The size and the weight of the individuals taken in Douglas Lake indicate that 

 conditions there are favorable to this species. The clear water and sand bottom are 

 well-known characteristics of its preferred habitat ; the pebble-strewn shallows, especially 

 those about the north end of Fairy Island, afford it ideal breeding grounds (Lydell, 

 1903; Reighard, 1906). 



The young of this species, together with those of the large-mouthed black bass, are 

 often seen on the sand shoals in late summer in pursuit of the mixed schools of young 

 suckers, perch, and spot-tailed minnows, which are common there. These they drive 

 toward shore into shallow water. The bass, which are then 2 or 3 inches long, are two 

 or three times as deep bodied as their intended victims, so that they are unable to 

 follow them into very shallow water. 



MiCROPTERUS s.'^LMOiDES (Lacepede), large-mouthed black bass, is not common in 

 Douglas Lake. It occurs in North Fishtail Bay, where the bottom is mucky in places 

 and the vegetation abundant, and is less common in other localities. We have records 

 of two taken in South Fishtail Bay. One measured 12 inches and weighed 30 ounces; 

 the other measured 14.4 inches and weighed 40 ounces. One contained a perch and the 

 other two fish and a crayfish. 



Fishermen tell of catching a peculiar bass on the "middle ground" to the east of 

 the north end of Fairy Island. The writer has never seen it. It is probably the large- 

 mouthed bass. 



The conditions in Douglas Lake can not be regarded as favorable to this species. 

 There is little mucky bottom in the shallow water, and few places afford the thick growth 

 of aquatic plants that the small-mouthed bass prefer for its breeding ground (Lydell, 

 1903; Reighard, 1906). 



Perca flavescens (Mitchell), yellow perch, is one of the most abundant fishes in 

 the lake. Our data concerning it are given in table viii. 



