KEPORT OF COMMISSIONER OF FISH AND FISHERIES. XXV 



hydraulic mining operations along the banks of the river and its tribu- 

 taries; they go up through the warm valley of the San Joaquin River, 

 lying in the second hottest summer area of the United States, in 

 large shoals, ascending the numerous side tributaries to their spawning- 

 grouuds. The hottest temperature area for the months of June, July, 

 and August, as shown by the temperature charts for the United States, 

 lately compiled for the Smithsonian Institution, is the region of the 

 Gila and mouth of the Colorado Rivers in Arizona Territory. The mean 

 for these mouths is 88° Fahrenheit. The valley of the San Joaquin, 

 portions of Arizona, and the lower valley of the Rio Grande River have 

 a mean of 84°. No other portion of the United States has so high a 

 summer mean. During the mouths of August and September, 1875, 

 temperature observations were made at the railroad bridges of the Cen- 

 tral Pacific Railroad.* The maximum, minimum, and mean tempera- 

 tures for the months of August and September were as follows : 



As referred to by Mr. Milner in a communication to the commissioners 

 of fisheries at their meeting in New York, February 10, 1875, the Sac- 

 ramento salmon, and especially the colony entering the San Joaquin 

 River, spawn in latitudes farther south than any anadromous species of 

 the genus Salmo. t 



In the report of the commissioners of fisheries of the State of Califor- 

 nia, for the years 1874 and 1875, the following statement is made with 

 reference to the Sacramento salmon : " Large numbers pass up the San 

 Joaquiu River for the purpose of spawning in July and August, swim- 

 ming for one hundred and fifty miles through the hottest valley in the 

 State, where the temperature of the air at noon is rarely less than 80° 

 Fah., and often as high as 105°, and where the average temperature of 

 the river at the bottom is 79° and at the surface 80°. The salmon of 

 the San Joaquin appear to be of the same variety as those in the Sac- 

 ramento, but average smaller in size." Leaving the bed of the San 

 Joaquin, they ascend the tributaries, the Merced, the Stanislaus, and 

 others, and find their spawning-grounds in the snow-fed sources of these 



# A series of observations were made on the temperature of the San Joaquin River, 

 California, through the kindness of Mr. B. B. Redding, of Sacramento, commissioner 

 for fisheries of California. 



t The trouts, Sahno fontinaJis, Mitch., in the Appalachian range, and Salmo pleuriticw, 

 Cope, of the headwaters of the Rio Grande River, extend their range to about the same 

 latitude, 37° N, as the San Joaquin salmon. 



