Sharks that do not bite

 Whale or shark? Whale sharks are called whale because of their immense size but they are fish not mammal, sharks that do not bite. Anjani Ganase recalls an encounter with a gentle giant.

 

Even though my job as a marine biologist has allowed me special encounters when working in the ocean environments, the whale shark seemed to be a creature of legends only heard about through chance encounters. Their mystery continued to build in my mind after several occasions of poor timing and missed opportunities where others in the cohort got the opportunity to see what these whale sharks were all about. I resigned to the fact that I probably would never see one, and it was at the moment – as usually happens when you go diving - that I got my first meeting with a whale shark.

 

We were surveying the reefs off Karimunjawa in Indonesia and as we swam along shallow coral reefs, we noticed a wall of fish cruising towards us. The fish were taking advantage of the slipstream of something massive.  It may have been a bow of the ship, but it moved silently – no rumbles of an engine. The large animal heading towards us turned out to be a whale shark – about 10 m in length – and cruised right over us. Before we could catch ourselves, the shark disappeared into the abyss, as quickly as it appeared. Just to give the title “biggest fish in the ocean” seems unworthy. The reverence that I have for whale sharks solidified in my mind with the need to learn more.

Whale Shark in Ras Mohammed National Park. Credit: Cinzia Osele Bismarck / Ocean Image Bank

Whale sharks have significance in cultures around the world. They are protected in places such as Indonesia, where they are seen as good luck by the fisherfolk. The largest marine protected area, Cenderawasih Bay, in West Papua, Indonesia, has one of the largest aggregations of whale sharks in the world. Fishermen often fed the sharks bit of bait fish to keep them around. Today, the whale sharks of Cenderawasih Bay are a major eco-tourism draw.

Unfortunately, many of these whale sharks migrate large distances and cross into other national territories that do not afford the same protection. Neighbouring countries such as China actively hunt whale sharks. Even if they are not hunted, the whale sharks often end up as by-catch on fishing vessels because of the indiscriminate methods of catching fish. This is one of the biggest threats to the species. Internationally, whale sharks are a threatened species, meaning that their numbers are declining globally. Like others in the family of sharks, there is high demand for their meat, skin and fins. The whale sharks in Cenderawasih Bay have an estimated economic value of 2.4 billion USD dollars, significantly more than what they fetch when caught and killed. The scheme to protect whale sharks and develop eco-tourism around them has also brought success to the fishing town of Oslob, The Philippines. The project shifted fisherfolk to eco tour guides. Even though the fishermen never hunted whale sharks, scientist claim that the shift in the jobs built the economy and improved food security and conservation.

Whale sharks are found all over the world, predominantly in tropical areas. In the west, whale sharks are known to aggregate off the Yucatan peninsula and seasonally migrate to several offshore banks in the Gulf of Mexico. In the southern Atlantic, observations of whale sharks have been made from the Brazilian coast to the African continent. Their migration routes are heavily influenced by food hotspots, such as upwelling areas rich in nutrients, plankton and bait fish. They may also migrate for mating. In the Caribbean, the occasional whale shark has been observed; they do roam in solitude on the open ocean. Random observations have been made off northeast Tobago, which runs close to the edge of the continental shelf.

Whale sharks are filter feeders and feed on plankton by cruising through the water column with mouths open. With abundance of food, whale sharks can grow to enormous lengths with record sizes of over 18 m (59 feet). However, they also grow extremely slowly, so the largest whale shark observed may be over a hundred years; one of the oldest shark was estimated to be 138 years. Female whale sharks get much larger than the males, but this is likely because they must carry their young. One female was recorded to carry about 300 shark pups inside. Slow maturation makes recovery of populations tricky as it takes a whale shark 30 years to mature and have young.

Whale sharks have amazing adaptations making them powerful swimmers and survivors in the open ocean. The unique pattern across the whale shark consists of background shades of greys, and blues overlaid with white spots. The pattern allows the shark to blend into the open ocean. The pattern of the white spots along the back of the whale shark is unique to the individual. Scientists have been able to identify and track whale shark individuals over the years by observing their spot patterns. Anyone who has recorded whale sharks can input their images or videos on whaleshark.org for identification. While whale sharks may have small eyes and poor vision, they have excellent senses of smell and hearing, and additional ability to sense vibrations from the tiny sensors on its skin called the Ampullae of Lorenzini, a trait that all sharks have. All these senses assist in finding food and avoiding danger. The skin of the whale shark is thick, about 14 cm thick in some places, and scientists have also shown that whale sharks are able to heal/ regenerate relatively quickly. These adaptations are essential as they tend to swim in shallow waters following their food is during the day, making them vulnerable to impacts from boats and propellors.

 

The whale shark is the largest fish in the ocean: it’s called whale because of its size but its biology is that of a shark. We know very little about the social structure and reproductive cycle of whale sharks. Much more research is essential to finding out more about the whale sharks to inform conservation. Even as we learn more and are able to protect their habitats and make sure they survive, we are assured that they will always be the majesties of the sea.

 

 

 

References

Anna, Zuzy, and Dicky Surya Saputra. "Economic valuation of whale shark tourism in cenderawasih bay National Park, Papua, Indonesia." Biodiversitas Journal of Biological Diversity 18.3 (2017): 1026-1034.

 

https://sta.uwi.edu/fst/lifesciences/sites/default/files/lifesciences/documents/ogatt/Rhincodon_typus%20-%20Whale%20Shark.pdf

 

Lowe, Judi, and Johann Friedrich C. Tejada. "The role of livelihoods in collective engagement in sustainable integrated coastal management: Oslob Whale Sharks." Ocean & Coastal Management 170 (2019): 80-92.

Martin, R. Aidan. "A review of behavioural ecology of whale sharks (Rhincodon typus)." Fisheries Research 84.1 (2007): 10-16.

Mark G. Meekan et al. Asymptotic Growth of Whale Sharks Suggests Sex-Specific Life-History Strategies. Front. Mar. Sci, published online September 16, 2020; doi: 10.3389/fmars.2020.575683

Womersley, Freya, et al. "Wound-healing capabilities of whale sharks (Rhincodon typus) and implications for conservation management." Conservation physiology 9.1 (2021): coaa120.