| Baseline data are lacking for all river dolphins worldwide. Inia geoffrensis and Sotalia fluviatilis occur in freshwaters of South America, and their distribution, relative abundance, seasonality, group size, site fidelity and movement, reproduction, and conservation status were investigated in Peru's Pacaya-Samiria National Reserve. Data collection took place between March 1996 and November 2000, and consisted of surveys of dolphins and habitat, photo-identification of individual dolphins, necropsies, and interviews with local people.;The encounter rates for botos (I. geoffrensis) and tucuxis (S. fluviatilis) were within the range of encounter rates for these dolphins elsewhere in South America. Abundance estimates were affected by survey methods, and strengths and weakness of various methods are discussed. Boto and tucuxi encounter rates were highest in confluences, intermediate in lakes, and lowest in rivers. Botos occurred in higher densities than tucuxis in lakes, confluences, and rivers, except the Maranon River. In general, encounter rates for botos and tucuxis in rivers and lakes did not differ among seasons. During low water, both species persisted longer in the confluences throughout the sampling day, and occurred in higher densities than in any other season; the reverse pattern was observed during high water.;In rivers and lakes, botos were seen most often as single animals and tucuxis were seen most often as singles or pairs. Significant seasonal differences in group size were not detected. Boto mating and calving occurred year-round, with boto calving peaking somewhat during failing water. Diurnal occurrence patterns were not detected for either species. There was no correlation between the occurrence of botos and tucuxis throughout the day in confluence areas. Twenty-four botos were identified and resighted. Maximum range was 220 km, with a mean range of 60 km (+/-61.05 SD).;River dolphin populations in the study area in the Pacaya-Samiria Reserve appear to be relatively healthy. Studies indicate that population numbers in the Samiria System have been stable over the last 10 years. Major threats are related to human fishing activity, and include entanglement in fishing gear and possibly poisoning to reduce net damage and predation on fish. Potential threats include boat strikes, oil spills, water and noise pollution, and overfishing of prey. |
