Eighty-five individual sharks were identified in a single season using photographs of their distinctive spot patterns.
An isolated ‘island continent’, famed for animals and plants that exist nowhere else in the world, Madagascar’s nutrient-rich waters are also home to an incredible array of marine life attracting increasing numbers of tourists.
The Madagascar whale sharks are primarily seen around the small island of Nosy Be, in the north west of the island. This area is a globally important hotspot for large marine species, including manta rays, sea turtles, humpback whales and even rare Omura’s whales.
The study is part of the Madagascar Whale Shark Project, a collaboration initiated in 2016 by researchers from the Marine Megafauna Foundation, Florida International University, and Mada Megafauna.
Lead author and project leader Stella Diamant said: “We’ve found that whale sharks regularly visit Nosy Be between September and December. That has led to a growing ecotourism 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.”
Whale sharks are the largest fish in the world, growing up to 20 meters long. However, the Madagascar whale sharks have been juveniles of less than nine meters.
“We identified 85 individual whale sharks over our first season in 2016. Some of the sharks were present across several months. They spend a lot of time in the area and seem to come here to feed,” Diamant said.
The marine biologists uploaded photographs of the sharks’ unique spot patterns to Wildbook for Whale Sharks (a global database of sightings) and compared them with data collected from known feeding areas in the Indian Ocean, including Djibouti, the Maldives, Mozambique, Seychelles and Tanzania, but found no overlap.
Whale sharks are filter feeders, consuming most of their food near the surface of the ocean.
“Whale sharks are a globally endangered species due to overfishing, accidental catches and boat strikes. Major declines in sightings have been seen in Mozambique, where we’ve documented a 79% decline in sightings since 2005, and the Seychelles. I was hoping that some of those sharks might have shifted over to Madagascar”, said co-author Dr Simon Pierce, co-founder and principal scientist at the Marine Megafauna Foundation.
“Unfortunately, that doesn’t seem to be the case. It’s great news for Madagascar though. These sharks can be a major asset for the country. There’s already a good marine ecotourism industry developing”, he added.
The Madagascar whale sharks are currently afforded no formal protection except in two Marine Protected Areas located to the southwest and northeast of Nosy Be. The island is a known location for shark fishing and finning.
“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 gillnets and industrial purse seiners operating offshore”, said Dr Jeremy J Kiszka, a marine biologist at Florida International University and co-scientific lead of the Madagascar Whale Shark Project.
Whale sharks are listed as ‘endangered’ on the IUCN Red List of Threatened Species since 2016 and received an Appendix I listing the UN Convention on Migratory Species in 2017. As a signatory to the Convention, Madagascar is obligated to protect the sharks and their migratory habitat in national waters.
The study was supported by Les Baleines Rand’eau, Aqua-Firma, PADI Foundation, IDEA WILD, Waterlust, the Shark Foundation, and two private trusts.
Stella Diamant, Christoph A Rohner, Jeremy J Kiszka, et al. ‘Movements and habitat use of satellite-tagged whale sharks off western Madagascar’ was published on 17 May 2018 and can be viewed here.
Interested in reading more about whale sharks? Oceanographic columnist Dr Simon Pierce, in Issue 01 of the magazine, discusses the curious case of the whale sharks of Mafia Island, perhaps the laziest and/or cleverest whale sharks in the world…
