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G. PILLERI 



lagoons are in winter, when the level of the water is low, full of buffeos whereas 

 there are hardly any animais in the rivers. This seasonal migration seems to dépend 

 on the depth of the water and the amount of food found in the lagoons or rivers. 

 Layne (1958) saw numerous animais in the lakes and lagoons one mile north of 

 Leticia (Upper Amazon, Peru). Thèse lagoons and lakes were ail connected to the 

 Amazon by canals. Inia and Sotalia were présent in the proportion 2:1. There 

 were 14 Inia in the three lakes in the early afternoon. He noted a migration from 

 the river to the lakes so that in the late afternoon, the number of animais in the 

 lakes had risen to 20-25. It is a pity that Layne concentrated his observations on 

 the lakes and not on the river as well. He mentioned that there were more Sotalia 

 in the river than Inia. I could not see that there was an increase in the number of 

 animais in the Rio Mamoré lagoon in the late afternoon. 



Man is an ecological factor of increasing importance in the biotop of the Inia. 

 Although the Inia seems to be shy, ranges with one to three animais are found 

 directly in front of small settlements. This was also true of Puerto Almacén where 

 2-3 animais were often seen swimming in the area between the western anchorage, 

 the Toribio canal to the Rio Mamoré and the stranded driftwood in the middle of 

 the Ibaré (fig. 1). Canoës and motor boats did not seem to disturb the animais at 

 ail unless they approached the animais directly. The .appearance of men and 

 dolphins in the same biotop is phylogenetically new and ha;> been described by 

 other species of river dolphins. Evidently the fishing villages along the banks of 

 the Irrawaddy river in Burma each have their own dolphin Orcella brevirostris 

 (flwninalis) which chases the fish into the nets (Anderson 1878). The Inia was 

 seen to behave in a similar manner by Lamb (1954). A buffeo helped the fishermen 

 to bring the fish from the deep to the shallower water. It reacted to the whistles of 

 the fishermen and remained for hours near their boats. This was an isolated case 

 by Inia. Nothing is known of similar behaviour by the Susu gangetica which 

 neurologically is much more primitive than the Inia and the Orcella (Pilleri 

 1966). However, I noted during my expédition to East Bengal in 1967 that the 

 Susu was often seen in areas of the Brahmaputra river directly opposite fishing 

 villages, similar to the habitat of the Inia in the Rio Ibaré. 



b) Enemies 



Nothing is known about the enemies of the Inia. Piranhas do not seem to 

 présent any danger to the buffeo. The skin seems to be able to offer enough 

 résistance to the sharp teeth of this dangerous animal. We could not find any 

 scars on the bodies of the captured Inias that could in any way be caused by the 

 teeth of a piranha. It is highly improbable that caymans would attack the Inia. 

 The reptile appears clumsy when compared with the lithe dolphin. The Inia is 

 probably as superior to the cayman as the oceanic dolphin is to the shark. 



