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

World of Animals - - Contents - Words Melissa Hob­son

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!

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