Date of Award


Document Type

Open Access Thesis

Degree Name

Master of Science (MS)


Environmental Sciences

First Advisor

Scott D. Kraus

Second Advisor

Robert E. Bowen

Third Advisor

Ellen M. Douglas


Populations of river dolphins throughout Asia are in decline as a direct result of intensified anthropogenic activity along river systems. Water development projects, land use change, contamination, and intensified fishing practices are known factors contributing to the probable extinction of the Yangtze river dolphin (Lipotes vexillifer) and declining populations of the South Asian river dolphin (Platanista gangetica spp.), Irrawady dolphin (Orcaella brevirostris), and finless porpoise (Neophocaena a. asiaeorientalis). Although not yet as extensive, river system development in South America is following a similar path as that of Asia, with impacts on dolphin species likely to follow. Currently, the Amazon river dolphin (Inia geoffrensis spp.), Tucuxi (Sotalia fluviatilis), and Guiana dolphin (Sotalia guianensis) of South America remain listed as data deficient. There is limited information regarding potential changes in their population sizes, distributions, and habitat suitability.

Broad scale population monitoring is needed in order to prioritize, direct, and evaluate conservation efforts. To be effective, monitoring methods should be relatively easy to implement, standardized, reliable, cost effective, sustainable over large spacial and temporal scales, and provide timely turnaround of data results. This thesis describes and demonstrates one such method for monitoring shifts in river dolphin distribution relative to anthropogenic development. Shifts is distribution offer an early indication of degraded habitat suitability, which is a precursor to population decline.

I conducted a passive acoustic survey of dolphin presence in two areas of the Amazon River subject to different degrees of human use; the inland port city Iquitos and the Pacaya-Samiria National Reserve (PSNR). Surveys were based on acoustic monitoring of biosonar activity. Recorders were distributed at 17 sites along 61 linear km of river habitat for durations of 46 to 148 hr. Dolphin presence was 45% lower near the city than in the reserve. This pilot study demonstrates the efficacy of acoustic monitoring as a method for testing dolphin redistribution and/or decline hypotheses in the context of anthropogenic development. I make recommendations for applying passive acoustic surveys to basin-wide monitoring of river dolphin populations. The methods are readily scalable and are applicable to continuous future monitoring and status assessment of river dolphins in South America as well as in Asia.