Marine scientists from UK have successfully demonstrated a novel method of identifying and counting whales using very high resolution satellite imagery, alongside image processing software, through the example of southern right whales breeding in part of the Golfo Nuevo, Península Valdés in Argentina.
The southern right whale, Eubalaena australis, is a baleen whale with a circumpolar distribution in the Southern Hemisphere. An adult female can reach a maximum size of 15 m and can weigh up to 47 tonnes.
Southern right whales were hunted extensively from the 17th through to the 20th century, causing their numbers to drop from an estimated 55,000-70,000 to around 300 by the 1920s.
Recent extreme right whale calf mortality events at Península Valdés, which constitutes the largest single population, have raised fresh concern for the future of the species.
To test the potential of using very high resolution satellite imagery to detect and count whales, Dr Peter Fretwell from the British Antarctic Survey and his colleagues used population of southern right whales in this region.
The satellite imagery was from the highest accuracy satellite, WorldView2, covered 40 square miles, and could penetrate further into the water column than images from other satellites.
“Whales populations have always been difficult to assess, traditional means of counting them are localized, expensive and lack accuracy. The ability to count whales automatically, over large areas in a cost effective way will be of great benefit to conservation efforts for this and potentially other whale species,” said Dr Fretwell, who is the first author of a paper published in the open-access journal PLoS ONE.
Three main criteria were used to identify whales: objects visible in the image should be the right size and shape; they should be in the right place and there should be no other types of objects that could be mistaken as whales.
The team manually identified 55 probable whales and 23 other features that could be whales on or just below the surface. In addition, the authors observed 13 objects only detected under certain wavelengths of light. Four different automatic detection methods were then tested against these numbers.
The automatic detection of whales was most accurate at specific wavelengths. The team concluded that these methods are more efficient than traditional methods of assessing populations of marine mammals, and may be used to calculate population abundance.
“This is a proof of concept study that proves whales can be identified and counted by satellite. Whale populations have always been difficult to assess; traditional means of counting them are localized, expensive and lack accuracy. The ability to count whales automatically, over large areas in a cost effective way will be of great benefit to conservation efforts for this and potentially other whale species,” Dr Fretwell said.
Previously, satellites have provided limited success in counting whales but their accuracy has improved in recent years.
Future satellite platforms will provide even high quality imagery and Worldview3 is planned to be launched this year. This will allow for greater confidence in identifying whales and differentiating mother and calf pairs. Such technological advancements may also allow scientists to apply this method to other whale species.
Fretwell PT et al. 2014. Whales from Space: Counting Southern Right Whales by Satellite. PLoS ONE 9(2): e88655; doi: 10.1371/journal.pone.0088655