Blue whales: first discovery near Seychelles in decades – what our research found | FIU news

Blue whales are fascinating animals. At 24 to 30 meters long (longer than a basketball court), they are the largest creatures on earth. They are also among the rarest. Estimates suggest there are only about 5,000 to 15,000 blue whales left in the world.

Their populations experienced an 89-97% decline due to worldwide commercial whaling activities that began in the North Atlantic Ocean in 1868. Blue whales were especially prized for their blubber, converted into oil and used in cosmetics and soaps, for the lubrication of industrial equipment, and as lamp oil. The last intentional catch of a blue whale was recorded off the coast of Spain in 1978.

Today, blue whales are found in all oceans except the Arctic. They usually migrate from their summer feeding grounds, where they feed almost exclusively on krill, to their winter breeding grounds. However, their migration patterns remain poorly understood, especially in the Indian Ocean where limited research has been conducted.

Historically, the Seychelles archipelago – off the coast of East Africa – was an opportunistic whaling ground for Soviet whaling fleets en route to and from Antarctica. In the waters of the northern Indian Ocean, whalers illegally killed more than 1,200 blue whales between 1963 and 1966, including 500 near the Seychelles.

Since then, no specific research has taken place to assess the abundance of blue whales in this region until 2020, when I collaborated with the University of Seychelles, Oceanic Films (UK) and my colleague, Kate Stafford, to investigate.

We conducted two expeditions in November 2020 and 2021. After surveying approximately 5,500 km across the northern Seychelles, we had a total of five sightings of up to ten blue whales.

This was a phenomenal finding. We were prepared not to see any blue whales due to the high level of hunting that took place quite recently and there was absolutely no information available since the last blue whale was killed in the region in 1964.

When blue whales were sighted, we slowly approached them to obtain details about their group size and behavior. Photographs were taken of both the left and right sides of the dorsal region to identify them.

Because the color patterns are unique to each animal, we knew that at least five individuals were identified during this expedition.

After sharing our photos with other research groups working on blue whales in the Indian Ocean, no match was found. This means that the whales we identified in the Seychelles may have been photographed for the first time ever!

Even though blue whales are no longer hunted and are protected by several international treaties, they are still listed as endangered on the IUCN (International Union for the Conservation of Nature) Red List of Threatened Species. They face a series of threats. For example, shipping traffic causes noise pollution that can disrupt communications and lead to collisions. Climate change is also affecting the distribution and abundance of their main food, krill.

Finding the whales

The vast oceanic habitat and elusive nature of the blue whale make them incredibly challenging to study. Furthermore, their deep dives and extensive migrations over thousands of kilometers pose logistical hurdles for researchers wanting to track their movements and behavior.

Understanding their ecology, population dynamics and conservation therefore requires innovative and resource-intensive research methods, such as systematic surveys from large ships or aircraft to assess their abundance or satellite tagging to investigate their movements and migrations.

Our expeditions consisted of visual surveys by ship, focusing on the deep waters (500-2,000 meters) off the northern part of the Mahé Plateau.

In addition, for over a year we placed a hydrophone (an underwater microphone that can record whale sounds) in an area where blue whales were likely to occur. This allowed us to confirm that blue whales in the Seychelles are more common than we thought, but very seasonal (even though we recorded blue whales all year round), mainly from December to April.

This method also revealed that our expeditions (in November 2020 and 2021) did not take place when blue whales were most abundant. It means that our future investigations will have to take place in the months of March and April, when their abundance is at its peak.

Their songs matched those of blue whales recorded near Sri Lanka (about 3,100 kilometers from the Seychelles), in the central tropical Indian Ocean. The seasonality in the Seychelles is similar to the presence of blue whales in Sri Lanka, which is also highest from December to April.

After scanning the ocean for five weeks, we recorded a total of 23 species of whales and dolphins in 30 days of active search efforts, which is remarkable.

We have recorded over 100 sightings of Bryde’s whales (Balaenoptera edeni), a non-migratory whale species that lives exclusively in tropical and subtropical waters, but also includes many sperm whales (Physeter macrocephalus) and beaked whales. The presence of all these species in the Seychelles suggests that the environment is productive enough to support large numbers of cetaceans. We will investigate this further in the future, especially to ensure that these special animals, including blue whales, continue to exist in these waters.

Of the four subspecies of blue whale known to exist, three are known in the Indian Ocean. We believe that the blue minke whale is the subspecies visiting the Seychelles, based on the physical characteristics of the animals we observed and, importantly, the nature of their calls.

The pygmy blue whale is generally smaller than other subspecies. It usually reaches a length of about 21-24 meters. Other subspecies of blue whales, such as the Antarctic blue whale, can grow to 30 meters or more. The pygmy blue whale is mainly found in the Southern Hemisphere and has acoustic characteristics that differ from others, especially Antarctic blue whales.

What’s next?

Due to our discoveries in blue whales, we have reached out to local tourism organizations and the government, especially to identify measures to limit the impact of the potential development of whale watching as an activity. These are positive steps towards its conservation. The involvement of local University of Seychelles students and young researchers is also critical to the long-term sustainability of research and conservation initiatives.

We still know so little about blue whales. But the data collected in the Seychelles gives us hope and encourages us to do more.

We now need to increase our research efforts to assess the abundance of these blue whales in the Seychelles and discover why they use Seychelles waters. Do they breed alone or feed in these waters, or both?

We also want to understand what they eat and how changing climate affects their distribution and behavior in the tropical waters of the Indian Ocean.

Jeremy Kiszka, Associate Professor, Institute for the Environment, Department of Coastlines and Oceans, Florida International University

This article is republished from The Conversation under a Creative Commons license. Read the original article.