This week’s Featured Species is my all time favorite shark- I actually have one tattooed on my foot! The Whale Shark (Rhincodon typus) is the largest shark in the world and the largest fish in the sea, measuring in at an astonishing 40+ feet (12.1+ m) and weighing nearly 60 tons (Skomal, 2016). But no need to fear this giant! Whale sharks are filter feeders, feeding on tiny microscopic plankton organisms (Stevens, 1997).
For its massive size, we know very little about whale sharks. Much of their reproductive mechanisms are known from only a single pregnant female which was commercially caught by harpoon in Taiwan in July 1995 (Joung, Chen, Clark, Uchida, & Huang, 1996). The “megamamma” was found to have over 300 developing embryos, all at different stages of development. Some still remained in their egg cases, while others were free of their egg cases and yolk sacs (Joung, et al., 1996). This suggests that the whale shark have long parturition periods and give birth in bursts over several days, weeks, or months as the young reach their fully developed neonate stage (Joung, et al., 1996). Since the discovery, both pregnant females and neonates have been documented in several areas throughout the world, suggesting these sites may be nursery habitats (Martin, 2007). However, no whale shark has ever been observed giving birth.
UPDATE! In June of 2019, a research team working on tagging and DNA sampling whale sharks in Ningaloo Reef, Western Australia witnessed whale shark mating behavior and captured the images on film for the first time ever! Tiffany Klein, a pilot with Ningaloo Aviation, was aerial spotting for CSIRO researchers when she spotted a large 30 foot (9 m) male approaching a smaller female. Read more here.
As I mentioned, the whale shark is a filter feeder species. It is one of only three filter feeding sharks: the whale shark, the basking shark (Cetorhinus maximus), and the megamouth shark (Megachasma pelagios). Unlike the basking shark, which relies on its forward momentum to pass plankton filled water over its gill rakers, the whale shark is capable of switching between the ram-jet method of the basking shark and vertical suction feeding at the surface (Martin, 2007; Skomal, 2016). Whale sharks have been observed completely vertical in the water with their mouths at the surface of the water, using a gulping technique to suction water into their mouths and over the gill rakers (Clark, & Nelson, 1997; Martin, 2007).
Whale sharks aggregate in large numbers seasonally in hot spots around the world, including the Belize, Australia, Maldives, and Mexico. These seasonal aggregations coincide with large plankton blooms and the spawning on several organisms including coral, snapper, and the megalopa of terrestrial crabs (Graham & Roberts, 2007; Heyman, Graham, Kjerfve, & Johannes, 2001; Martin, 2007). Their seasonal predictability in tropical and subtropical coastal waters and docile disposition, whale shark ecotourism has become a booming industry!
Authority: Smith, 1828
Family: Rhincodontidae, 1 species
Length: Maximum of 41 feet (12.5 m)
Weight: Up to 60 tons
Habitat: Continental and island shelves, coastal waters, coral reefs, open ocean
Depth: Surface down to depths of 2300 feet (701 m)
Litter Range: 300 + pups
Home Range: Worldwide in tropical and warm temperate waters
Diet: Plankton, slightly larger free swimming marine animals
IUCN Status: Endangered
(Pierce, & Norman, 2016; Parker, 2008; Skomal, 2016)
I am so excited to begin my conservation internship this month in La Paz, Baja California Sur, Mexico on a whale shark photo identification project. Be sure to check back over the next few weeks for updates from La Paz!
The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!
Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.
Featured Image Source
Handwerk, B. (Author). (2016 August 29). Whale Shark [Digital Image]. Retrieved from http://www.nationalgeographic.com.au/animals/secrets-of-whale-sharks-revealed.aspx
Clark, E., & Nelson, D. R. (1997). Young whale sharks, Rhincodon typus, feeding on a copepod bloom near La Paz, Mexico. Environmental Biology of Fishes, 50(1), 63-73.
Graham, R. T., & Roberts, C. M. (2007). Assessing the size, growth rate and structure of a seasonal population of whale sharks (Rhincodon typus Smith 1828) using conventional tagging and photo identification. Fisheries Research, 84(1), 71–80.
Heyman, W. D., Graham, R. T., Kjerfve, B., & Johannes, R. E. (2001). Whale sharks Rhincodon typus aggregate to feed on fish spawn in Belize. Marine Ecology Progress Series, 215(MAY), 275–282.
Joung, S.-J., Chen, C.-T., Clark, E., Uchida, S., & Huang, W. Y. P. (1996). The whale shark, Rhincodon typus, is a livebearer: 300 embryos found in one “megamamma” supreme. Biology of Fishes, 46(Baughman 1955), 219–223.
Martin, R. A. (2007). A review of behavioural ecology of whale sharks (Rhincodon typus). Fisheries Research, 84(1), 10–16.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Pierce, S.J. & Norman, B. 2016. Rhincodon typus. The IUCN Red List of Threatened Species 2016: e.T19488A2365291.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.