RELATION OF MAMMALS TO FISHES 125 



During the salmon run in Alaskan rivers bears gorge themselves 

 with fish. 10 Dogs also eat spawning salmon in streams of the North- 

 west and contract the "salmon disease," an intestinal trematode dis- 

 ease, the salmon from salt water not thus affecting them. 11 The do- 

 mestic cat sometimes catches fish close to shore in shallow water. 12 

 Wildcats eat both fish and frogs, and in 118 stomachs 6 per cent of 

 the contents consisted of fish, probably bait used in the traps. 13 Coyotes 

 sometimes eat both fish and reptiles, three horned lizards having been 

 found in one stomach. 14 The name of the South American rat genus 

 Ichthyomys** seems to have been derived from its fish-eating proclivity. 

 There is one genus of fish-eating bats (Noctilio) in the Caribbean 

 region, 'some stomachs examined containing fish exclusively. 16 Several 

 instances are mentioned of deer eating fish, 17 a habit perhaps acquired 

 through the eating of refuse about camps. 



Beaver, though semi-aquatic, are vegetarians and do not indulge 

 very much, if at all, in a fish diet. However, they do affect the fish 

 population of beaver streams in other important ways. Their dams 

 form quiet pools, ponds and lakes whose somewhat complex effect 

 upon fishes has been partly investigated and much discussed. There 

 seems good reason for the belief that in regions where the summer 

 temperature of the water is high and the flooded areas contain much 

 vegetation that decomposes in the ponds, they may be decidedly detri- 

 mental to fish life, especially for some time after the ponds are freshly 

 formed. In rapid streams of high, cool mountain areas, beaver ponds 

 are often very beneficial to fishes, affording protection to young trout 

 and equalizing the flow of water, keeping the streams running during 

 dry seasons. Often in such regions the old, well-established beaver 

 pools afford the best fishing. 18 



Though many mammals, as we have seen, eat fish, many species of 



10 Osgood, N. Amer. Fauna, No. 24, p. 43, 1904 



11 Dpnham, Science, LXI, 341, 1925. 



12 Dimmock, Amer. Naturalist, xvni, 941-943, 1884. 



13 Dixon, Journ. Mammalogy, vi, 36-38, 1925. Howell, N. Amer. Fauna, No. 45, 

 p. 42, 1921. 



"Lantz, U. S. Biol. Surv. Bull. No. 20, 1005. 



"Thomas, On a new fish-eating rat from Bogota, Ann. and Mag. Nat. Hist., Ser. 

 9, xni, 164, 1924; A new fish-eating rat from Equador, ibid., p. 541; Journ. Mam- 

 malogy, v, 215, 1924. 



"Goodwin, Journ. Mammalogy, ix, 104-112, 1928. Benedict, Journ. Mammalogy, 

 ix, 58-59, 1928. 



" Burgess, Journ. Mammalogy, v, 64-65, 1924. 



"Bailey, U. S. Dept. Agric. Tech. Bull. No. 21, 1927 (replacing Dept. Bull. No. 

 1078, 1922). Dearborn, U. S. Dept. Agric. Circular No. 135, p. 10, 1920. Kendall, 

 Roosevelt Wild Life Bull, n, 205-351, 1924; iv, 286-491, 1927. Knight, Science, LXII, 

 59O-59I, 1925; LXIII, 209-210, 1926. 



