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Island of the Sharks
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Ask The Expert
Set 6, posted October 16, 1998
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Question:

I would like to know what a whale fish looks like, and would like to know if it is one of the biggest sharks. Thank you very much.

Katherine
Arlington, TX
BROWNBONE@webtv.net



Response from Dr. Klimley:

The whale shark, Rhincodon typus, is the largest of sharks, reaching 18 meters long (54 feet). The shark has a broad flat head with its mouth at the end with filter screens on its internal gill slits to gather large plankton, on which it feeds. The shark has prominent ridges on the side of the body with its top dorsal and second dorsal fins toward the rear of the body. It has a unique checkboard pattern of light spots separated by horizontal and vertical stripes on a dark background.

The shark is found in subtropical and tropical seas around the Earth. It is an oceanic species that occasionally comes close to shore and enters the lagoons of coral atolls. I have encountered several of these sharks within the Gulf of California. One shark was mammoth in size, appearing to be seven times the length of a free diver who swam along the shark. The shark is an egg layer. Their prey are small crustaceans, small fishes, and occasionally larger fishes. Individuals feed at the surface, at times assuming a vertical posture and bobbing up and down, capturing prey on the upward movement.

This huge shark is harmless to humans.

For more information on the species, read the following paper:

Wolfson, F.H. 1986. Occurrences of the whale shark, Phincodon typus Smith. Pp. 208-226 in Uyeno, T., R. Arai, T. Taniuchi, and K. Matuura (Eds.), Indo-Pacific Fish Biology: Proceedings of the Second International Conference on Indo-Pacific Fishes. Ichyological Society of Japan, Tokyo.



Question:

I know scalloped hammerheads (Sphryna lewini) give live birth, but I am curious as to their mating. Do they have any rituals, and has anyone ever observed them mating? At Sea World San Antonio, we have adult scalloped hammerhead sharks and have never seen them mate or even seem interested, unlike the reef whitetips, reef blacktips, and nurse sharks. Thanks.

(name witheld by request)



Response from Dr. Klimley:

The behavior and ecology of hammerhead sharks has been described mainly from observations of schools of hammerhead sharks that gather at the Espiritu Santo seamount (i.e., underwater mountain) in the Gulf of California near the tip of the Baja Peninsula. I will briefly describe the sequence of behavior leading to mating. See the references below for a scientific and popular article describing this ritual in detail.

The hammerhead schools consist of variously sized females that fight among one another for a central position within the school. The larger females force the smaller ones outward by either directly striking them with the underside of their snout or frightening them away with a ritualized behavior, consisting of a reverse flip and a full twist. When males arrive at these groups, they rapidly swim into the center of the school where the largest, most fit females are located. The males their mid-section to the side spasmodically while rotating their clasper back and forth. The clasper is a scroll-like organ formed from the pelvic fins through which sperm is inserted into the female's cloaca. However, the clasper serves another purpose here: as a signaling device advertising the male's presence and his willingness to choose a partner with which to mate.

The male then selects a female, and the two swim away from the school. Howard Hall, an underwater cinematographer, filmed a male hammerhead with his clasper inserted in a female at the seamount. It is likely that the male bites the female on a fin as, in other species, this induces the female to roll onto her backside and permit the male to insert its clasper in her.

Klimley, A.P. 1995. "Hammerhead city." Natural History, 104:32-39 (popular article). Klimley, A.P. 1985. "Schooling in the large predator, Sphyrna lewini, a species with low risk of predation: a non-egalitarian state." Ethology, 70:297-319 (scientific article).




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