Whales from space
Satellite images have been identified as a useful and feasible tool for whale density observations in a study led by the British Antarctic Survey, published in Nature Scientific Reports on July 31,2020. The research provides a clear comparison between space-borne derived density estimates and traditional ship survey estimates.
What are the implications of being able to assess whale densities from space and why do cetaceans deserve our full attention? Let’s take a closer look at the unseen world of whales and how remote sensing surveys might be the key to their conservation.
The unseen world of cetaceans
It is a well-known fact that among all animals on Earth, some of the largest species are the marine mammals known as whales, with the blue whale being on top of the list. However, what is not as well-known is that these mammals are also amongst the most intelligent species ever discovered, with neuroscientists around the world debating the enormous cognitive capabilities of these cetaceans. From developing complex communications combining clicks, whistles and pulse calls, to having distinct regional dialects and accents, and exhibiting social behaviours, whales are undeniably living rich and complex lives away from the human eye.
As an illustration, orcas have the most gyrified brain in the world, which indirectly measures the brain cell communication speed (the wrinklier, the better). By comparison their gyrencephaly index (GI) is 5.7, while for humans it is 2.2. Additionally, the cetacean brain has developed a unique lobe, called the Paralimbic lobe, which connects the emotional systems to the abstract thinking. That, coupled with a highly developed amygdala and with the most elaborated insular cortex analysed to this day, is proof enough that cetaceans are capable of very complex emotions and self-awareness. No wonder why whales have shown signs of empathy, humour and even mischievousness, while dolphins are known to give names to one another by using a signature whistle. Fun fact, orcas and dolphins are among the very few mammalians capable of vocal production learning, a key characteristic of human speech.
It is of interest to note that while some dolphins are reported to have learned English, up to 50 words used in correct context, no human being has been reported to have learned dolphinese.
Carl Sagan
Importance of satellites for marine ecosystems
As we have already established in previous articles, remote sensing data is crucial for the study of hard to reach areas, such as the Antarctic territories or the global ocean in this case. With about 71% of the Earth being covered in water and nautical exploration about as old as humans, it may be surprising to know that more than 80% of the ocean remains unexplored to this day. What is more, only around 7.45% (total area of 26,984,530 km2) of the Earth’s oceans are identified as Marine Protected Areas, also known as MPAs. Locally, the Scottish MPA Network comprises around 22% of the Scottish seas.
Why are satellites important to marine ecosystems?
In brief, satellites can offer a generalised cost-effective view over the marine environments, without the need of travelling. Additionally, satellite imagery is essential to provide information that would otherwise be very difficult to obtain from Earth-based surveys alone, such as the overall sea surface temperature, marine wildlife tracking or illegal fishing activities to only name a few. For this reason, satellite remote sensing is an established technique when it comes to environmental monitoring ecology and impact assessment, as well as aiding the conservation efforts of threatened and endangered marine animals.
If we look at cetaceans in particular, satellites have proved useful in detecting and counting different species of whales. Furthermore, remote sensing surveys are able to determine stranded whales in inaccessible areas, which in turns allows scientists to quickly arrive on site and examine the scene. This leads to a better understanding of the stranding cause, as well as help mitigate the issues. On top of that, satellites are used to track whale migratory movements, which is of great importance in determining high-priority habitats and mass behavioural changes. This information is crucial in the development of conservation management strategies and in the designation of new Marine Protected Areas.
Why should cetaceans catch our full attention now? All things considered, whales are a big part of the marine ecosystem and thus are an indicator of the overall health of Earth’s oceans. Historically, commercial whaling decreased their numbers greatly, and their exact number today, together with their conservation status, remain highly uncertain. More than 20% of the cetacean species are classified as threatened on the Species Red List of the International Union for Conservation of Nature (IUCN), nonetheless around 50% of species could not be evaluated. Simply put, to ensure the protection of endangered species and prevent further extinctions, scientists need to first identify which types are threatened and in need of our immediate attention.
Unfortunately, the data we have today is not sufficient to determine a threat category for half of the cetacean species. As an example, the brainy orcas from the beginning of the article are among the species without a clear international conservation status.
Whale monitoring: satellite imagery vs shipborne surveys
A study led by the British Antarctic Survey (BAS) has found satellite imagery to be a viable way of evaluating densities of whale populations. The satellite data collected by the WorldView-3 satellite was compared with information retrieved from classical ship-based surveys gathered at a similar time. Hence, by comparing both density estimates it was demonstrated that satellite imagery is indeed a feasible tool in whale density studies. In spite having a lesser detection rate (1/3 of the ship density estimates), the spatial and temporal scales of space-based observations cannot be matched by any ground monitoring method.
The technique has the capability of complementing traditional survey data, thus showing very promising opportunities for future research, especially for areas where in-situ surveys are difficult to perform. The cost-efficient and risk-free observation tool has important implications in studying the recovery rate of whales post the commercial exploitation era, as well as in determining their habitat use patterns.
The study was conducted on a data sample of approximately 1000km2, located in the Gerlache Strait region in the Western Antarctic Peninsula. The area is a known cetacean summer feeding ground, dominated by baleen humpback whales.
The next step in satellite whale observations is unbiased classification, which can be achieved automatically by using well-trained machine learning algorithms. The exciting work is already underway and rapidly developing, as space-borne surveys are becoming more and more popular when it comes to remote wildlife study.
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