The new whale shark hotspot
This year, a world-first study by the Madagascar Whale Shark Project revealed the island is a feeding hotspot for juvenile whale sharks, an aquatic leviathan that can be found throughout Earth’s tropical waters
Discover why Madagascar is the place to see Earth’s largest fish
The Madagascar Whale Shark Project’s findings have identified Nosy Be in northwest Madagascar as a globally important hotspot for juvenile whale sharks, in addition to the manta rays, sea turtles, humpback whales and Omura’s whales that can also be found in the area. This news could give a huge boost to the island’s developing eco-tourism industry by attracting more tourists to the area to see these gentle giants.
The new study, which was published in the journal Endangered Species Research, revealed that juvenile whale sharks swim to Madagascar to feed. An encouraging 85 individual sharks were identified in a single season using photographs of their distinctive spot patterns. All the sharks were juveniles at less than nine metres (29.5 feet) in length.
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 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 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 evidence of any overlap.
“The Madagascar Whale Shark Project’s findings have identified Nosy Be as a globally important hotspot”
As part of this study, the team attached eight satellite tags to immature whale sharks to track their movements in near real time. They found that the sharks spent most of their time in shallow waters between 27.5 and 30 degrees Celsius (81.5 and 86 degrees Fahrenheit) around the tagging area in Nosy Be.
Half of the tagged sharks also visited a second hotspot near Pointe d’Analalava, 180 kilometres (111.8 miles) south of Nosy Be. Five of the sharks swam over to Mayotte and the Comoros islands, and two swam right down to the southern end of Madagascar. One of those sharks then swam back to Nosy Be, a total track of 4,275 kilometres (2,656.4 miles).
“It was exciting to see that there is a second hotspot for the sharks in the area. We will be exploring the area later this year,” explained Diamant. “Madagascar clearly provides an important seasonal habitat for these young whale sharks, so we need to ensure they are effectively protected in the country.”
Whale sharks get their name from their enormous size. The largest fish on Earth, these mammoth animals can reach over ten metres (32.8 feet) in length, a weight in excess of 20 tons and have skin ten centimetres (3.9 inches) thick, which is thicker than any other animal. Despite their size, these gentle giants are completely harmless to humans, which means you can jump into the water and snorkel with them – without needing a scuba diving qualification – at the shallow feeding aggregations where they can be found.
Because tourists travel across the globe to share the water with these mesmerising sharks, the species has a huge eco-tourism value to the destinations in which it can be found. These include the tropical and subtropical waters of the Philippines, Australia, Mexico, the Maldives and, of course, Madagascar. They congregate in these areas searching for food during plankton blooms and are also thought to use the Galápagos as a breeding area because of the number of large adult females seen there.
Alongside the basking shark and megamouth shark, whale sharks are one of just three species of filterfeeding shark. They eat tiny prey such as copepods and zooplankton, using their gills to sift their meal from the water like a coffee strainer. While they’re not particularly intelligent, whale sharks are very talented at finding food. They have an acute sense of smell, which they use to sniff out plankton, and scientists have found plankton densities around ten-times higher than normal in areas where whale sharks are feeding. They can feed passively by opening their mouth and swimming along, filtering all the plankton they find in their path, or by using suction to actively take in water and gulp their prey down with it.
While still only in their juvenile stage these gigantic sharks need to consume around 21 kilograms (46.3 pounds) of plankton daily in order to sustain themselves, and this requires feeding for over seven hours each day. This is because while they can filter seawater incredibly quickly – around 600,000 litres per hour – they can only sieve two or three kilograms (4.4 to 6.6 pounds) of plankton from this much water.
Whale sharks have been classified as Endangered on the IUCN Red List of Threatened Species since 2016. Dr Simon Pierce, co-founder of the Marine Megafauna Foundation, explains why they are in such a dire situation.
“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 per cent decline in sightings since 2005.”
The main threat to whale sharks is from directed fisheries, which often take whale sharks as trophies or use their fins as a sign above shops that sell shark fin soup. They can also become accidental bycatch for tuna trawlers and other fishermen or be struck by boats. In some areas, such as Qatar, there are even movements to create ‘go-slow’ zones to encourage boats to lower their
“These gigantic sharks need to consume around 21 kilograms (46.3 pounds) of plankton daily, which requires feeding for over seven hours”
speed to reduce the chance of the animals being harmed or killed by boat strikes.
The work being done to protect whale sharks is critical, particularly because they’re very slow to grow and don’t reach sexual maturity until around the age of 30. It’s thought that the full lifespan of a whale shark is around 70 to 100 years, but no one has been able to confirm this. Scientists can check their age by X-raying their spine and counting the rings on their vertebrae, but because this is the only method that can be used it’s not currently possible to age a live whale shark.
Despite global research efforts, there’s still a lot we don’t know about whale sharks. For example, they can dive to depths of over 1,800 metres (5,905.1 feet), but we don’t know why they swim that deep. It’s thought they might be going to those depths to use the Earth’s magnetic field to improve their orientation, but this hasn’t been confirmed. We also don’t know much about how they reproduce, and no one has ever seen a whale shark give birth.
The only pregnant female to have been physically examined was accidentally caught by a Taiwanese fishery and sadly drowned in the net. The fishermen realised she was pregnant and passed her onto scientists to examine; they found 304 pups inside her. Astoundingly, despite being likely to have had the same father, the entire litter was split into three different maturity stages: from eggs to embryos and finally baby sharks almost ready to be born. This has led scientists to believe that female whale sharks can store semen after mating and then impregnate themselves when they have the most energy and conditions are most suitable for them to reproduce.
In addition to the cutting-edge – and often expensive – research being undertaken by marine biologists to find out more about whale sharks and their habitats, such as satellite tagging, the public can also get involved in conservation efforts through citizen science projects such as Wildbook for Whale Sharks.
Individual whale sharks can be identified by the unique spotted pattern behind their gill slits and above their pectoral fin. This means that any tourists who snorkel with a whale shark can take a photo of this area and submit their picture to WhaleShark.org to help researchers identify which shark they saw. Through this global sightings database citizen scientists can help researchers to collect much more data than they would be able to collate alone.
Sophisticated star-mapping technology, originally designed by NASA to help the Hubble Telescope orient itself in space, is used to recognise the sharks’ spot patterns so researchers can log how many individuals have been seen and track their movements over time.
Marine megafauna such as whale sharks play a critical role in the health of our oceans’ vast ecosystems, so it’s vital the species is protected: if we protect these ocean giants other marine species will thrive as a result. Marine conservation charities such as the Marine Megafauna Foundation are working to save them through a combination of pioneering research, education and the creation of sustainable conservation solutions. There’s a lot to do, but if researchers, citizen scientists and policymakers can work together, there is hope for the future of this endangered species
ABOVE Stella Diamant (left), founder of the Madagascar Whale Shark Project, with a tagged shark
TOP LEFT These leviathans swim at an average speed of just 5kph (3.1mph), but they can achieve 9.7kph (6mph) in short bursts among other threats, this globally endangered species is at risk from boat strikes. The spot patterns on a whale shark’s back are unique to each individual, so scientists can use photo identifications to track which sharks they’ve seen. Madagascar is a known location for shark fishing and finning. whale sharks are currently afforded no formal protection except in two Marine Protected areas located to the southwest and northeast of Nosy Be. anyone who snorkels with a whale shark – even if they’re not a scientist – can submit a picture to WhaleShark.org to help conservation research.
ABOVE Whale sharks grow up fast – one captive pup went from 0.8kg (1.7Ib) to a whopping 151.2kg (333.4Ib) in just over three years!