378 



SCIENCE 



[N. S. Vol. LIII. No. 1373 



of Peruvian Amazonia. I liad during the 

 Irwin Expedition collected on the upper por- 

 tion of this river. 



These streams, the Ucayali, Maranon, and 

 Huallaga, are comparable in size to the Ohio 

 at flood stage. All arise in the Andes and 

 form a vast confluent flood plain parallel to 

 the mountains, and 500-600 miles in extent. 

 Though 2,000-2,500 miles from the mouth of 

 the Amazon, this plain is only 400 feet above 

 sea level. In all this stretch there is very 

 little topographic relief. The annual fluctua- 

 tion in level of the Amazon at Iquitos is 40 

 feet. The annual inundation therefore extends 

 far inland from the rivers. Large numbers of 

 cut-off lakes (cochas) with their connecting 

 cana3 form a network throughout the system, 

 which becomes one body of water with the 

 coming of winter rains. Most of them are 

 dead-water bayous of varying dimensions. 

 There are almost no brooks — all depressions 

 iquebradas) only serving to receive the back- 

 water of the rivers. The smaller tributary 

 rivers vary greatly in their flow at all sea- 

 sons, fluctuating both with the local rainfall 

 and with the level of the outlet. A stream 

 flowing very rapidly now may display almost 

 no current within a few hours, or vice versa. 



The extent of the navigable portion of the 

 streams in Peru is much greater than in most 

 Brazilian streams. Many of the latter are 

 interrupted not far from their mouths by im- 

 passible rapids. The Brazilian river basins 

 are sharply separated from each other by 

 chains of hills. To the Loretan the slightest 

 rise is a cerro — mountain. Any stretch of 

 terrain not inundated is an altura. Every 

 riffle is a pongo — rapid. Within the past few 

 years even the redoubtable Pongo de Man- 

 seriche, by which the Maranon breaks through 

 its last chain of the Andes, has been passed 

 by no fewer than flve steam launches. It has 

 always been risked by raft and canoe. 



The above conditions allow many species 

 of fish from the lower Amazon to become dis- 

 tributed to the very foot of the Andes, and 

 throughout oriental Peru. One finds many 

 fishes extending from one extremity of Loreto 

 to the other. 



With the annual subsidence of the water 

 there is of course everywhere a local sorting 

 of species according to preferred habitat. 

 Thus in a given stream one may not obtain 

 more than two, three, or half a dozen species 

 at the same time. Earely are more than this 

 number brought up in a single haul of a 

 seine. (Bates called attention to this fact 

 seventy years ago.) The cochas usually pro- 

 duce more species, but spaced pretty well 

 apart. To get them all one must draw the 

 seine many times in various parts of the lake. 

 The conunon fish that one is obliged to reject 

 may surfeit even one's native helpers. There 

 is a pretty rigid assorting of fishes into river 

 and lake forms, despite the fluvial origin of 

 the lakes, and despite the inundations. 



The gi-eat diversity of arboreal animals on 

 the land is paralleled in the water by the 

 large number of families of fishes and of 

 aquatic mammals represented. The region is 

 yet virtually tourist-free. One may journey 

 by steamers and launches without seeing 

 much of the teeming life of forest and river, 

 or of primitive human life. Only in the 

 tributary sti-eams, traveling by canoe, does 

 one encounter them. Here the dolphin, man- 

 atee, otter, alligator, capybara, tapir, etc., 

 still abound, and one comes surprisingly near 

 seeing all the animals which he had hoped to 

 encounter. 



The year 1920 was remarkable for its un- 

 usual rainfall. Not only was the curve for 

 the depth of the Amazon at Iquitos higher 

 throughout April and May than for many 

 years, but also throughout the dry season. 

 The lowest stage reached was some seven feet 

 higher than the mean minimum depth. 



The exceptional inundation of April and 

 May had destroyed much of the crops. There 

 was a serious shortage of all staples (plan- 

 tains, beans, yucca, rice, etc.) and consider- 

 able hardship among the improvident. At no 

 time were the sand bars of the Maranon or 

 Amazon exposed. This of course affected the 

 fishing industry. Seining was made much 

 more difiicult, while throw-net fishing was 

 probably increased, due to the concentration 

 of the mijanos, schools of shore fish. Much 



