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Dead sperm whale in The Wash, East Anglia, England. © CSIP-ZSL.

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Sperm whale (physeter macrocephalus) Gulf of California. The tail of a sperm whale.

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An eye high in the sky …?

Scientists have recently advanced a method for counting whales from space. Until now, to count whales, you either had to be working from land – which could limit the distance you can survey, a boat – which could disturb the whales, an airplane – which can be dangerous and disturb the whales or more recently a drone – which in themselves have some very exciting prospects but are still a relatively new concept and need further testing. All techniques except land-based watching have associated costs (some exceptionally high) and possible negative impacts on the whales being studied, however the idea of being able to gather information from a satellite that is located far above the earth has great potential but at the same time, for the moment anyway, some serious restrictions.

This particular study focused effort on a known population of southern right whales that spend their summer months in the nursery grounds of Peninsula Valdes, Chubut Province, Argentina. The behaviour of these whales, with mothers calving in very shallow waters in protected bays, made them an ideal candidate for testing out the validity of using satellite imagery for counting whales. A small area of the bay was chosen and both manual and automated searches of the images were conducted. Results showed that the automated search found approximately 90% of the individuals identified in the manual search. 

As already mentioned however, this method of “counting whales” does have some limitations and it is important to keep these in mind.

This test worked (in part) because the researchers knew that no other large marine mammals are reported to use this bay. They knew therefore that they would only be counting southern right whales because although they claim that current satellite imagery can be used to identify individual whales both at, and just below the surface it is not possible to differentiate between species. Additionally, subsurface rocks in very shallow areas, boats and even rafting groups of seabirds are among the things that can confuse the camera by “looking” like a whale, resulting in incorrect estimates. As we know, whales are also not at the surface all the time therefore this method only acknowledges whales at the surface and disregards those that are not. Not all species aggregate as these southern right whales do and most importantly not all whales spend extended time at or near the surface in a shallow bay with clear water. This kind of imagery is also useless in areas of bad weather resulting in rough seas (which in reality is where a lot of whales, dolphins and porpoises live) and areas with murky waters, for example in rivers or estuaries where there is a lot of silt or fresh and salt water mixing. It is of course important to remember that this method  is to be used for “counting whales” as opposed to “identifying habitat”, otherwise whales and dolphins in areas that have not been deemed to be important habitat, or indeed the corridors in-between, could be at even greater risk from entanglement and vessel strikes.

However, on a more positive note, several species of whale do breed in areas of calm water where, in order to protect their vulnerable calves, females remain close to the surface. These behaviours would potentially allow the satellite images to be used for population estimates however the limitations noted above must be taken into consideration. One possibility would be to have a stationary satellite above a specific location where whales were reliably known to frequent, unfortunately however these are hugely expensive. As the resolution of the satellite images increases and image analysis also improves, the scientists believe that they should be able to monitor many more species and in other types of location.

Only time will tell … but we remain intrigued all the same.