Observations on Freshwater Dolphins in the Upper Amazon

Abstract

Although freshwater dolphins of the families Platanistidae and Delphinidae are among the more interesting and conspicuous members of the Amazon River fauna of South America, relatively little is known of their habits. The Amazon dolphin or bouto, Inia geoffrensis (Blainville), occurs throughout much of the Amazon and its principal affluents and in the Orinoco as well. River dolphins of the genus Sotalia also inhabit a considerable portion of the Amazon system, their range extending to over 1,600 miles above the mouth of the river. In February, 1956, an expedition sponsored by Florida's Silver Springs was made to the upper Amazon at Leticia in the Commissary of Amazonas in southern Columbia to collect living freshwater dolphins for exhibition purposes. Both Inia and Sotalia were present in some numbers in the region visited, and four Amazon dolphins, which had been harpooned and captured alive, were obtained from natives and flown from Leticia to Florida. Of the four, one young female died en route and a young male succumbed shortly after arrival. The two surviving dolphins, both males, were kept at Silver Springs near Ocala, Florida. As a member of this party, the writer had excellent opportunities to study Inia and Sotalia in their natural surroundings over a 15-day period from February 19 to March 2. Observations were largely confined to the environs of Leticia, although some data were obtained at the settlement of Ramon Castilho, Peru, directly across the river from Leticia, and in the vicinity of Benjamin Constant, Brazil (Fig. 1). The dolphins were watched daily for periods ranging from an hour or two to nearly the entire day. In addition, several night trips were made to investigate the extent of their nocturnal activity. The majority of observations were made from a 16-foot aluminum boat equipped with an outboard motor or …