Cetacean Society International

Whales Alive!

Vol. VIII No. 2 April 1999


River Dolphins In The Bolivian Amazon

by Tamara L. McGuire


Tamara L. McGuire, a river dolphin expert at Texas A&M University, recently received CSI support to work in Bolivia. She was so determined to help some local scientists learn the latest scientific techniques, and advance knowledge on this regional population, that she would have taken out a personal loan to get there. Her language and cultural skills are major factors in her success. Tamara is unique; we salute her spirit, energy, and willingness to help others. This is her report.

The river dolphin Inia geoffrensis is found in the freshwater rivers of the Amazon and Orinoco basins of South America. Inia are known by several common names, including tonina and bufeo rosado (Spanish), boto (Portuguese) and pink river dolphin (English). The International Union for the Conservation of Nature has classified Inia as vulnerable. River dolphins have been studied in Venezuela, Perú, Colombia, Brazil, and Ecuador. There are no records of long-term population studies in the Bolivian Amazon. No one knows how many Inia there are in South America, as population estimates of river dolphins have been problematic. The majority of studies report results in terms of relative densities or encounter rates, as true densities are difficult to obtain because of the complex habitat, elusive behavior, and often patchy distribution of river dolphins.

In the summer of 1998, I was invited to participate in the first systematic river dolphin survey of the Bolivian Amazon. Healy Hamilton, a doctoral student at U.C. Berkeley, is conducting a genetic study of the river dolphins in South America. As part of her cooperative research agreement with the Bolivian government, she is supporting the work of Enzo Aliaga Rossel, a Bolivian undergraduate of the University Mayor de San Andres, in La Paz. For his thesis project in biology, Mr. Rossel wanted to conduct the first population estimate of Bolivian Inia. As he and Ms. Hamilton lacked previous experience in this type of work, they asked me to join them last August on a research cruise in the Bolivian Amazon. I am a doctoral student in the Marine Mammal Program, Dept. of Wildlife and Fisheries Sciences, Texas A&M University. The title of my dissertation work is "Distribution and abundance of river dolphins in the Perúvian Amazon", and I have been studying river dolphins in the Perúvian Amazon for the last 3 years. Before that, I lived in the Venezuelan llanos where I studied the ecology of the river dolphin Inia for my master's research. During our study of August and September 1998, our objectives were to: (1) estimate river dolphin abundances; (2) characterize dolphin habitat with regard to hydrology, water quality, and bank-structure; (3) develop and evaluate a standard, yet flexible technique for estimating river dolphin densities; and, (4) opportunistically necropsy river dolphin carcasses. Our overriding objective was to get Enzo up and running on his own investigation of the dolphins in the Bolivian Amazon, and we hope that he will use the methods he learned during this pilot study as the basis for his own long-term investigation. This study will provide much-needed baseline information on distribution and relative abundance of river dolphins in the region.

The study area is located in the Bolivian Amazon, which is in the tropical lowlands of a country that is more famous for its Andean mountains and highland culture. We traveled north, down the Mamore river, from the town of Trinidad to the town of Santa Ana de Yacuma, surveying the Mamore River for dolphins on the trip down-river and then back up. We also surveyed selected tributaries for dolphins, and characterized the aquatic habitat and water quality. The data was collected primarily from the platform of riverboat, which was also our floating home for the duration of the study. Observations in narrow tributaries were made from a skiff with an outboard motor. Because of the large study area, we used sampling methods in selected areas, rather than a direct count of the entire area. This was a non-invasive study and data from live animals was collected by observation alone. No tissue samples were taken from live animals for Hamilton's own genetic study. Any dead Inia encountered in the study area were necropsied following standard procedures.

In total, we spent 15 days on the river, and logged over 62 hours of survey effort. We spent many more hours simply observing the dolphins and photographing them. We surveyed over 226 linear km of the Mamore river (twice), in addition to surveying four of its tributaries. We saw many Inia, including several newborns and juveniles, which suggests that the population is relatively healthy. We also observed two dead dolphins, but were unable to determine the cause of death. Enzo is analyzing the data to obtain density estimates, and has since returned to the study area three times, in order to compare dolphins' distribution and abundances at different water levels during the seasonal flood cycle. He plans to complete his thesis, and thus obtain his title of Biologist, by the year 2000.

I feel so privileged to have been able to participate in this study and to see the Bolivian Amazon and its dolphins. The wildlife in the region is still quite abundant and it impressed me as much more plentiful than I have seen in national parks in the Venezuelan llanos and Perú's Pacaya-Samiria Reserve. Fortunately, the human population of the Bolivian Amazon is still relatively low, although this may be soon changing due to resettlement programs of the Bolivian government. It is fortunate that Enzo is beginning his study now as it appears to be a critical time in which to start collecting baseline data on the distribution and conservation status of the river dolphins in Bolivia. Participation in this study has helped my own research as well, as it has given me a broader perspective by observing river dolphins in a new (to me) part of their range. For example, we saw dolphins that were gray, which is what I have observed in Venezuela, but we also saw several bright pink dolphins, which is what I have seen in Perú. Equally important, this trip provided me with the opportunity to meet and work closely with new colleagues in a field that has not always been known for its spirit of cooperation.

A grant from Cetacean Society International made it possible for me to travel from my research site in the Pacaya-Samiria Reserve, Perú, to La Paz Bolivia, and then on to the town of Trinidad. Additional logistical and financial support for my participation was provided by the Marine Mammal Program at Texas A&M University, the American Cetacean Society, Ms. Lucille Moore, and by Oceanic Society Expeditions.

Enzo, Healy and I sincerely thank the members of Cetacean Society International for their support of this collaborative project.


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