Satellites Sneak a Peak at Tiny Dolphins
April 30, 2010
Franciscana dolphins are a mysterious lot.
They belong to the river dolphin family, but they don’t swim in rivers. They prefer the coasts. They are one of the smallest cetaceans in the world, and their populations don’t mingle with each other in expected ways.
So scientists are pulling out all the stops to learn more about Franciscanas, also called La Plata dolphins. They are doing so in an effort to save them. With information taken from the high seas and the high sky (really high), conservationists from WCS, Columbia University, the American Museum of Natural History, and Fundación AquaMarina are gathering clues to how to best protect these cetaceans. Their new study has combined imagery shown via satellites orbiting the Earth with genetic data collected from the dolphins themselves.
What the conservationists discovered is that there may be two or three distinct populations of this dolphin.
The genetic research compiled DNA differences between the dolphins found in certain areas. The satellite data showed how these areas compared environmentally with the others. The sea’s temperature, turbidity (how clear it is), and levels of chlorophyll seem to matter to the Franciscanas. In some cases, populations of these little cetaceans living close to each other were more genetically dissimilar than those dolphins swimming in waters hundreds of miles away.
“The availability of both genetic and environmental data provided us with a rare opportunity to examine how ecological factors affect population structure in a marine species,” said Martin Mendez, the study’s lead author. “In this instance, the study subject is possibly the most endangered cetacean in South America, so delineating populations and the factors that create them certainly plays an important role in conservation measures.”
At 5 to 6 feet in length and between 80 and 90 pounds on average, Franciscanas are small but they have big problems with getting tangled and drowning in fishing nets.
The researchers compared 275 DNA samples from dolphins that had been stranded, entangled in fishing gear, or captured and released in six locations along Argentina’s coast (the species ranges as far north as southern Brazil). Genetic markers then allowed the scientists to statistically gauge the gene flow between the groups at different sites.
How these dolphins act may also hint to how their population structures evolved. The Franciscanas’ mitochondrial DNA, which is inherited only through the dolphin mother, and their nuclear DNA, passed down from both mother and father, reinforced the current understanding of cetacean behavior. Basically, female dolphins stay close to the waters where they were born, while male dolphins travel more widely. Of course, environmental barriers, such as the type of seawater they must swim through, could steer these males to more similar seas.
“We’re only beginning to understand the interactions between environmental factors and population patterns in marine environments,” said Dr. Howard Rosenbaum, director of WCS’s Ocean Giants Program. “What this study shows is that marine systems are not homogeneous environments, but full of variations that could play important roles in shaping and reinforcing how animal populations use their habitat. These types of information are essential for developing strategies on how best to protect these coastal dolphins and broader marine spatial planning.”