Kauai Sea Tours


Basic Shark Biology - Part Two



Can you tell the difference between a male & female shark? Yes, a male shark has two claspers which are modifications of the pelvic fin (located on the belly of the shark). A clasper can be as long as a person's arm on a mature male. There are two claspers, each with visible hooks on the tips of the clasper. Normally only one clasper is inserted into the female. Once inserted, there is a rotation of the cartilage which results in a hook piercing the inner walls of the female oviduct, anchoring the male organ in the female; hence, the name "clasper".


How do sharks mate & is there any courtship? For the large species of shark almost nothing is known about mating "where, when & how often" are unknown. There are only a few species in which actual copulation has been observed. For the white-tip reef sharks, the sharks engage in precopulatory courtship biting. The smaller male will grip the female's pectoral fin in his teeth preparatory to entwining his body beneath her & inserting a clasper into her cloacal opening. The sharks will sink to the bottom until copulation is complete. It is thought that in some species the female gives off a pheromone, a sex attractant substance.

            In some species of sharks, such as the Blue shark, sperm can be stored in a shell gland for later use until the eggs are mature or go directly to fertilize mature eggs.


How are young sharks born, live or from eggs? There are 3 possibilities for sharks. 1) Some species lay eggs usually encased in a leathery shell, they are expelled into the sea where the embryos develop for a period of 6-10 months hatching as miniature adults. This is considered the most primitive mechanism known as oviparous which means egg birth, & it is used mostly by bottom dwelling types of sharks such as the horn & cat sharks. 2) Ovoviviparous, meaning born live from egg, is the mechanism that occurs in the majority of sharks. The eggs develop from the nutrition of the yolk, & the embryos hatch inside the mother, to be born shortly after. With some species the developing embryos will actually feed on the other embryos inside the mother, cannibalizing one another till the most ferocious remain. This is referred to as ovophagy, which means egg eating & occurs with the Mako, Tiger, Sand & probably the Great White. 3) Viviparous, meaning live birth, is the mechanism in which there is a placenta-like growth contacting the embryo's yolk-sac & provides a channel for transmission of nutrients direct from the female's blood stream to the embryo (takes 9 months for development). This is the most sophisticated mechanism of development. It occurs in the Blue shark, Oceanic White tip, Black tip reef, Gray reef, & probably all of the hammerheads.

            Some species of shark will not hesitate to eat their own young, thus females will not eat at all while they are in the nursery grounds during "pupping" season.


Is it true, that sharks have to swim to breathe? Sharks have been thought to be destined to a life without rest, because some need to swim continuously in order to move water past the gills to oxygenate the blood. However, a substantial number of species are quite capable of resting on the bottom in still water, while muscularly pumping water over the gills. It is probably the case for larger species, including the Tiger shark, Bull shark, and Gray reef shark.


How fast can sharks swim? They normally don't swim fast & actually average less than 1 mile per hour. The fastest shark is the Mako shark which can swim to at least 22 mph, before leaping 20 feet into the air. Mako is the only shark fast enough to successfully hunt the Blue Marlin. Great whites & Blue sharks are also considered to be capable of short bursts of fast swimming.


How deep do sharks dive? Some species of shark (i.e. Cookie Cutter) lie at the bottom of the sea more than 2 miles deep & then swim up in the evening for feeding.


How old do sharks live? Sharks are aged by counting the number of rings (annuli) added yearly to the sharks' vertebral centra (annulus method). It is not an exact method as some species may differ in the number of rings they add each year. The Tiger shark can probably live 50 years & the Great White almost 100 years. The average is close to 25 years of age.


Are there any fresh water sharks? Yes, out of the hundreds of species, there are two that can live in fresh water the Bull & Ganges shark. The Bull shark is found in the Lake Nicaragua, & many rivers; including, Mississippi, Amazon, Ganges, & Tigris in Nicaragua. The Ganges shark is rare & is only found in the Hooghly & Ganges Rivers in India.


What is the largest shark? The largest shark & fish is the Whale Shark, & it is a filter feeder-practically harmless, similar to a Baleen whale except that it has 1000's of tiny teeth arranged in over 300 rows. The whale shark feeds on plankton, shrimp & small fish. The average whale shark is around 50-60 feet & weighs 45 tons. The whale shark can have 300 eggs; it is thought to be ovoviviparous meaning born live from egg. The eggs are carried internally until they hatch inside & then the "pups" are born.

            The smallest shark is the Dwarf shark or Spined pygmy which averages almost 4 inches in length, the longest recorded was 9.8 inches.


Is it true the Great White Shark is the only shark that lifts its head out of the water to inspect surface objects? Yes


Why is shark skin often called "skin teeth"? Shark skin is made up of tiny, hard, tooth-like scales called denticles (denticle means tooth). These denticles have a hard outer layer of enamel & are extremely abrasive. The shark's "skin teeth" reduces water turbulences & increases laminar flow there by enabling them to move more efficiently in the water.


What shark holds the known record for the longest distance traveled? The Blue shark holds the record 3,740 miles, the distance from New York State to Brazil or a little more than one way trip to Alaska from Hawaii.


Shark Attacks in the Hawaiian Isles from 1779-1996 (taken from G. Balazs, National Marine Fisheries Service) There have been 115 attacks since 1779. According to type of activity - swimming/snorkeling (#1), surf boarding (#2), & getting swept out to sea from shore (#3) - give the highest statistics for shark attacks. The greatest number of attacks (26 out of 115) occurred from 1990-1995 & the second greatest number (24 out of 115) occurred from 1980-1989. With respect to the time of year, more shark attacks occur during April. June, November & December are all tied as having the second highest number of shark attacks. Oahu leads the islands in having the highest number of documented shark attacks including fatalities (47 out of 115 with 21 fatalities); Maui is second (27 out of 115 with 8 fatalities); the Big Island is third (17 out of 115 with 12 fatalities); & Kauai is fourth (15 out of 115 with 5 fatalities).


How did the Hawaiians view the sharks in their waters? The Hawaiians have always had great respect for sharks especially the Tiger & Great Whites. The mana or spirit of the Great White was embodied in the motif represented as an abstraction of the shark teeth (equilateral triangles) woven into the chief's feathered cloak & also in complex tattoo motifs of the Hawaiian warriors. The teeth from the Great White presented the sharpest & thinnest edge used to cut designs for kappa or bark cloth bamboo stampers, wooden kappa beaters, & decorative bases for drum & gourds. Teeth fastened to heavy wood clubs were formidable weapons. Shark skin produces a leather that has 2-3 times the tensile strength of pig or cow hide & it was used to make head covers of the Hawaiian hula drums.

            Thirty-three years ago, people paid to see young men riding on the backs of large Tiger sharks - it was considered a grand tradition of Oahu. It was the shark aquarium which is now a research facility of University of Hawaii to study captive dolphins.

What is the latest in technology for protecting humans from shark attacks? The U.S. Navy has designed and tested the "shark screen" - a large, dark, cylindrical plastic bag which is closed at the bottom, and has inflatable rings around the top. The idea is NOT to have any protruding areas (i.e. arms or legs), or any blood or body chemicals-only a large shapeless image is presented to the shark. "Shark screen" seems to be successful; probably a tent or sleeping bag would work as general survival gear.

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