Blue whales have been discovered to frequent the seas around Seychelles on a seasonal basis, according to the first dedicated scientific survey to be carried out in the Indian Ocean islands.
The world’s biggest animals, blue whales (Balaenoptera musculus) are now known to be present regularly between December and April, though exactly why they visit the western tropical Indian Ocean remains unclear. Extended acoustic monitoring has matched the population to that known from the north-western part of the ocean, near Sri Lanka.
Historically, the Seychelles archipelago was an opportunistic whaling ground for fleets passing to and from the Antarctic, according to the study, which was produced by scientists from the University of Seychelles, Florida International University (FIU) and Oregon State University (OSU). Soviet whalers illegally killed 500 blue whales near Seychelles during the 1960s.
After the country joined the International Whaling Commission in 1978 and became part of the Indian Ocean Whale Sanctuary, it started lobbying to protect whales in the Indian Ocean.
The scientific team undertook two expeditions to determine the distribution of blue whales, obtain photo-identification data and collect the first acoustic data on the species in the region, using a hydrophone that was deployed for a year.
Over two field seasons in the past five years they established the presence of blue whales through five confirmed sightings of up to 10 animals. There are four subspecies of blue whale but from their song it was determined to be the pygmy blue whale that visits Seychelles waters. These have a maximum length of 24m compared to the 30m attainable by other subspecies.
Challenging to monitor
Before the new study, blue whales had proved a “rare and challenging to monitor” species in the western tropical Indian Ocean, says the Geneva-based Save Our Seas Foundation (SOSF).
One of the SOSF's project leaders investigating the importance of Seychelles for cetaceans is FIU biology professor Dr Jeremy Kiszka, a research associate at the Island Biodiversity & Conservation Centre at the University of Seychelles and a co-author of the study.
“It is remarkable to know that the largest animal on Earth swims here,” he said. “Blue whales are protected because they are no longer legally hunted, but they still face a range of threats. Shipping traffic causes noise pollution and can lead to collisions. Climate change is changing the distribution and abundance of their key food, krill.
“We now need to increase our research efforts to assess the abundance of these blue whales and discover why they are using Seychelles waters. We also need to raise awareness and help the government to protect them better.”
Kiszka, one of the featured scientists in a new documentary, Blue Whales – Return of the Giants, says he hopes that further dedicated research can address such questions as what the whales do while in Seychelles, what they eat and how climate change might affect their movements.
“These blue whales have no borders; we need to conduct research on an appropriate scale, and we need to collaborate internationally,” he said. “It’s a phenomenal opportunity to understand these blue whales.” The study has been published in the journal Endangered Species Research.
Also on Divernet: Whale song reveals lost population, 2020: a good year for blue whales, Female killers v blue whale – a world-first, Blue whales back in Spanish killing grounds, Blue whales: Too busy eating to sing
