Ecological factors influencing groups sizes of river dolphins (Inia and Sotalia). Marine Mammal Science. In press.

Project Details

Date : 2011
Volunteer Name : Gómez-Salazar, C.; Trujillo, F.; Whitehead, H.
Category : ,

Project Description

Abstract: Living in groups is usually driven by predation and competition for resources. River dolphins do not have natural predators but inhabit dynamic systems with predictable seasonal shifts. These ecological features may provide some insight into the forces driving group formation and help us to answer questions such as why river dolphins have some of the smallest group sizes of cetaceans, and why group sizes vary with time and place. We analyzed observations of group size for Inia and Sotalia over a 9-year period. In the Amazon, largest group sizes occurred in main rivers and lakes, particularly during the low water season when resources are concentrated; smaller group sizes occurred in constricted waters (channels, tributaries, and confluences) which receive an influx of blackwaters that are poor in nutrients and sediments. In the Orinoco, largest group sizes occurred during the transitional water season when the aquatic productivity increases. Largest group size of Inia occurred in the Orinoco location which contains the influx of two highly productive whitewater rivers. Flood pulses govern productivity and major biological factors of these river basins. Any threats to flood pulses will likely have an effect on the functionality of these ecosystems and the species living in them.