The Whale Shark (Rhincodon typus) by Maddie Hitzeman
Understanding the Whale Shark
Despite its name, the Rhincodon typus, otherwise known as the Whale Shark is neither whale nor shark. The Whale Shark is actually the biggest fish in the sea reaching an average length of forty feet and weighing about ten tons. Whale Sharks are carnivores, but contrary to what you would expect, they do not use their hundreds of small teeth for feeding. Whale Sharks are mainly filter feeders, catching their prey- primarily dog snapper and cubera snapper eggs- in their four-foot wide mouth and filtering out the water through their gills. In addition to their distinctly wide mouth, they are characterized by their gray, brown, or bluish coloring, their light spots between pale vertical and horizontal lines on their backs, and their white underside. Although the reason for their disruptive body pattern remains unknown, scientists believe that they are either the result of evolution from living at greater depths where disruptive patterns are used to camouflage or because it protects them from ultraviolet radiation since they spend most of their time near the surface of the water.
If you’ve seen Pixar’s motion picture, “Finding Dory”, you might recognize a whale shark named Destiny. If not, you may recognize a real whale shark.Habitat and Geographical Distribution
The whale shark can be found in two parts of the world: either in the tropical environment of the Atlantic Ocean (25% of the global population) or in the warm waters of the Indo-Pacific Ocean (75% of the global population). Through genetic research, we have found that these two subpopulations function independent of each other. All whale sharks enjoy warmer waters, usually between 26.5 and 30 degrees Celsius and their occurrence and abundance depends on cyclicals, or long-term climate shifts. Whale sharks also congregate where food is abundant, but don’t usually interact as a community or family. The whale shark spend most of its time in the epipelagic zone to feed during seasonal fish spawning events or zooplankton blooms; they also feed on mesopelagic organisms which is why they are sometimes found diving depths of up to two thousand meters.The Whale Shark can usually be found in more tropical waters indicated by the red.
Biology and Reproduction
Whale Sharks are a K-selected species and are ovoviviparous meaning the egg hatches in the uteri of the Whale Shark and the female has a live birth. Whale Sharks populate in Taiwan and the Kurashio Current waters during the summer for birthing.
Little is known about Whale Shark age and growth due to variation, but researchers estimate that male Whale Sharks begin maturing at 17 years of age and female Whale Sharks mature between 19 to 22 years of age. Whale Sharks are born at a length of 21 to 25 inches and reach full maturity at a length of approximately 9m. Their lifespan is about 60 years and their generation length is approximately 25 years. This comes to show how vulnerable the Whale Shark is to extinction and how long and difficult the recovery process can be. Whale Shark numbers are dwindling, and as we will discover, it is much easier to kill Whale Sharks than to save them.Declining Population
In 2001, the declining Whale Shark population caught the attention of conservationists, earning this fantastical fish a spot on the list of vulnerable species. As of March 18th of this year, the Whale Shark is now listed endangered due to bycatch threats, vessel interference, and the Whale Shark trade. As of today, 7,011 individuals have been identified as the global population by using a database that matches the identifiable patterns of individual whale sharks. Unfortunately, the Whale Shark population is predominantly juvenile male sharks, inaccurately representing the female population. In the Indo-Pacific region, there has been a population decline of 63%; in the Atlantic, a population decline of 30%; and a world-wide decline of 50%.
At the star of 1977, Whale Shark meat became the most expensive shark meat at $13.93/kg resulting in the death of over 272 individuals. Later that same year, the demand for Whale Shark declined most likely due to local stock depletion. Today, Taiwan kills an average of 1,0000 Whale Sharks every year for their meat, creating a national and international market for Whale Shark. In Orient and Hong Kong, there is a high demand for Whale Shark fin and a possible international trade with the Philippines. In contrast, the Philippine fin trade is only a small portion of the Philippines’ contribution to the declining Whale Shark population. In local fishing communities, the Philippines utilize Whale shark meat for food and Whale Shark liver oil to waterproof their boats. Finally, India eats Whale Shark and uses their oil for their boats as well as for medicine and other appliances.
Another reason for their decline is large and small scale bycatch. Since Whale Sharks congregate in areas of large zooplankton blooms along with tuna and other targets of fisheries, Whale Sharks are often victims of bycatch. Since Whale Sharks spend most their time near the surface of the water, the most common form of bycatch is by purse seine; when fisheries enclose large numbers of fish in one large net, Whale Sharks get trapped along with them.
Finally, vessel interference, especially vessel strikes, poses a threat to declining Whale Shark populations. Since Whale Sharks swim near the surface, they are prone to strikes from fishing and tourist vessels. Although Western Australia and other areas frequented by Whale Sharks are protected from fisheries, some question if tourism has any affect on Whale Sharks. A researcher named Brad Norman and his team did a study in Ningaloo Reef, Australia- a popular tourist destination to see Whale Sharks- to observe if the tourists had any affect on the behavior of Whale Sharks. They concluded, by evidence of what they call a “critter cam”(1) that the tourists themselves do not affect the Whale Sharks. Although tourists do not affect Whale Sharks, the vessels driven by this $5 million industry can cause harm to the Whale Sharks through vessel strikes, noise disturbance, and habitat destruction.
Recovery Plan
In order to keep this big fish swimming, conservationists’ goal is to maintain protected areas around Australia and to expand protection into the Indo-Pacific and Atlantic areas. Actions to reach this goal include increasing cooperation with other areas of the world to expand Whale Shark protection through thorough mentioning of multiple endangerment acts and lists, and monitoring the many people that visit Australia to determine the impact of tourism on Whale Shark populations and develop possible responses.
Additional probable actions include more restrictive tourist rules to reduce human interference, protecting highly populated Whale Shark destinations from water ways and vessel traffic, and monitoring fisheries’ catches and enforcing justice for those who catch, trade, and harm the protected Whale Shark.Click here for more information about the Whale Shark Recovery Plan!
What Can You Do?
