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Whale Shark Biology and Life History

Information on the biology and life history of whale sharks is scant at best. Because of their migratory behavior and their pelagic lifestyle, it is difficult and costly to conduct long-term studies. In addition, due to their protected status, acquiring information on their life history (age, growth, and reproduction) is infrequent, primarily coming from stranded specimens that have washed ashore or caught accidentally in fishing gear (See Conservation).The maximum size, age at sexual maturity, and longevity of whale sharks are poorly documented. One researcher suggested that whale sharks might not reach maturity until 30 years of age and could live as long as 60 years (Taylor 1994). It is thought that males mature at a smaller size and earlier age than females. Pai et al. (1983) reported a mature male eight meters in total length and three immature females between eight and nine meters. Estimates of age at maturity for males range between 20-27 years of age, whereas females probably mature at an older age (Wintner 2000).

Interestingly, only a few records exist of whale sharks less than three meters in total length. Of those the smallest range in size between 55 and 93 cm, total length (Colman 1997). Most specimens are reported between four and 10 meters in length. The only defense a whale shark has is its size, so small juvenile whale sharks can be very susceptible to predation. The lack of whale shark specimens less than three meters in length has prompted some researchers to speculate that small whale sharks have a rapid growth rate (Chang et. al., 1997). Whale sharks have the ability to make deep dives to 2000 m (Graham et al., 2006). Scientists have proposed that young whale sharks may spend the first part of their lives in the deep ocean, exploiting the concentration of marine life (euphausiids, myctophids, squid, jellyfish) at the “deep scattering layer” (Wilson et al., 2006).

Historically, there was much debate over the reproductive strategy of whale sharks. In 1953, a large egg case containing a whale shark embryo was collected in a shrimp trawl off the Texas coast, suggesting oviparity (egg-laying) as the mode of development (Baughman 1955). However, a pregnant female (10.6 m) harpooned near Taiwan in 1995 contained 300 embryos at various stages of development and revealed that whale sharks utilize yolk-dependent viviparity (where embryos rely solely on their yolk-sacs for nutrients during their entire development) (Joung et al. 1996). This finding suggested that waters off of southeast Taiwan may be an important pupping area during the summer months. The majority of sightings in the northern Gulf are of immature sharks, possibly indicating this area may serve as a nursery ground (Hoffmayer et al. 2005).

Literature Cited

Wilson, S.G., J.J. Polovina, B.S. Stewart, and M.G. Meekan. 2006. Movements of whale sharks (Rhincodon typus) tagged at Ningaloo Reef, Western Australia. Marine Biology 148:1157-1166.

Baughman, J.L. 1955. The oviparity of the whale shark, Rhincodon typus, with records of this and other fishes in Texas waters. Copeia 1955:54-55.

Chang, Wen-Been, Leu, Ming_Yih, and Fang, Lee-Shing. 1997. Embryos of the Whale Shark, Rhincodon typus: Early Growth and Size Distribution. Copeia 2:444-446.

Colman, J.G. 1997. A review of the biology and ecology of the whale shark. Journal of Fish Biology 51:1219-1234.

Graham, R.T., C.M. Roberts, and J.C.R. Smart. 2006. Diving behaviour of whale sharks in relation to a predictable food pulse. Journal of The Royal Society Interface 3(6):109-116.

Hoffmayer, E.R., J.S. Franks, and J.P. Shelley. 2005. Recent observations of the whale shark (Rhincodon typus) in the north central Gulf of Mexico. Gulf and Caribbean Research 17:117-120.

Joung, S.J., C.T. Chen, E. Clark, S. Uchida, and W.Y.P Huang. 1996. The whale shark, Rhincodon typus, is a livebearer: 300 embryos found in one ‘megamamma’ supreme. Environmental Biology of Fishes 46:219-223.

Pai, M.V., G. Nandakumar, and K.Y. Telang. 1983. On a whale shark, Rhineodon typus, Smith landed at Karwar, Karnataka. Indian Journal of Fisheries 30: 157-160

Taylor, G. 1994. Whale Sharks, the Giants of Ningaloo Reef. Angus and Robertson, Sydney, 174 pp.

Wintner, S.P. 2000. Preliminary study of vertebral growth rings in the whale shark, Rhincodon typus, from the east coast of South Africa. Environmental Biology of Fishes 59:441-451.