Madagascar recognised as whale-shark hotspot
Eighty-five individual sharks, all less than 9m in length, were identified in a single season by marine biologists, with some of the animals staying for several months at a time.
The study is part of the Madagascar Whale Shark Project, a collaboration initiated in 2016 by researchers from the Marine Megafauna Foundation (MMF), Florida International University, and Mada Megafauna.
Whale sharks are primarily seen around the small island of Nosy Be, in north-west Madagascar.
Described as an isolated "island-continent” known for its many endemic terrestrial species, Madagascar’s nutrient-rich waters attract much marine life, says the report, including manta rays, turtles, humpback and rare Omura’s whales.
“We’ve found that whale sharks regularly visit Nosy Be between September and December,” said lead author and project leader Stella Diamant.
“That has led to a growing eco-tourism industry, as people travel to see and swim with these gigantic, harmless sharks. We’re still learning about their population structure and movement patterns, but it’s clear the area is an important hotspot for the species.”
The researchers uploaded photographs of the sharks’ unique spot patterns to the Wildbook for Whale Sharks global sightings database to compare them with data collected from known feeding areas in the Indian Ocean, including Djibouti, the Maldives, Mozambique, Seychelles and Tanzania, but found no overlap.
They also attached eight satellite tags to track the whale sharks' movements in near real-time, and found that they spent most of their time in shallow waters between 27.5-30°C around the Nosy Be tagging area.
Half of the tagged sharks also visited a second hotspot near Pointe d’Analalava, 110 miles south of Nosy Be, an area the scientists plan to explore later this year.
Five of the whale sharks swam to Mayotte and the Comoros islands, and two to the southern end of Madagascar – one of these sharks then returned to Nosy Be, a 2660-mile journey. Three sharks were resighted near Nosy Be the following season after having lost their tags. Whale sharks are slow swimmers but still travel an average 13 miles a day.
“Madagascar clearly provides an important seasonal habitat for these young whale sharks, so we need to ensure that they are effectively protected in the country,” said Diamant.
Whale sharks are listed as Endangered on the IUCN Red List of Threatened Species and received an Appendix I listing in the UN Convention on Migratory Species in 2017.
As a signatory Madagascar is obligated to protect the sharks and their migratory habitat in national waters, but at present the only formal protection from shark fisheries it provides is in the form of two Marine Protected Areas to the south-west and north-east of Nosy Be.
“Over the last decade, shark populations have declined dramatically in Madagascar due to overfishing. However, the most significant threat to this species is the incidental catch in coastal gill-nets and industrial purse-seiners operating offshore,” said Dr Jeremy J Kiszka, a marine biologist at Florida International University and co-scientific lead of the project
The study Movements and Habitat Use of Satellite-Tagged Whale Sharks off Western Madagascar is published in the journal Endangered Species Research and can be accessed here.
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