A. Longevity
1. Little is known about the growth and age of elasmobranchs. Many of the conventional methods for aging animals, such as examining teeth, will not work with elasmobranchs.
2. Sharks grow slowly compared to bony fishes, possibly due to sharks'slow digestive time and feeding rates. There is considerable variation in age and growth rates between species and even between populations of the same species.
B. Aging studies
1 . Growth rings are periodically deposited on the vertebrae of some sharks. Vertebrae can be stained and examined for these growth rings. Growth rings may stop developing in older sharks.
2. Examining the vertebrae of captive-born sharks after their death enables researchers to compare the number of growth rings with the shark's known age
. 3. In some areas, tagged sharks are providing information about growth rates. Once a shark is caught, it is measured, tagged, and released. The shark is measured again when it is recaptured. Researchers correlate the measurements with the number of years since recapture and calculate a yearly growth rate.
C. Predators
Depending on the species, sharks and batoids have several predators, including other sharks, elephant seals, and killer whales.
D. Human interaction
1. Sharks are vulnerable to overfishing. Because sharks are slow-growing and a single female produces only a few hundred pups or less in a lifetime, depleted populations may take years to recover.
a. Recreational and commercial shark harvesting has increased in the past several years due to an increased demand for sharks and shark products.
b. Each year, thousands of sharks are taken unintentionally in nets set out to catch other types of fish. c. One particularly wasteful type of shark fishing is known as fanning. Only the fins of the shark, which will be sold for use in sharkfin soup, are removed. The rest of the shark is simply discarded.
2. Fisheries management programs are necessary for a sensible shark harvest.
a. The National Marine Fisheries Service (NMFS) develops management plans for sharks, setting catch quotas for target shark species.
b. On April 26, 1993, NMFS implemented a plan to manage U.S. shark fisheries of the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. The plan includes the following features:
(1) Annual commercial quotas, which are divided into half-yearly quotas.
(2) Provisions for closing a fishery for a species group when the semi-annual quota is met.
(3) Catch limits for recreational anglers.
(4) Permit requirements for commercial vessels that catch sharks.
(5) A requirement that vessels land fins in proportion to carcasses (effectively prohibiting the practice of shark finning).
(6) A requirement that when sharks are not kept, they are released in a manner that ensures the probability that they will survive.
3. Future research into the population dynamics of commercially important shark species will yield important information about longevity, reproduction, and growth. This information can be used to design effective fisheries management programs.
Scientific Classification | Habitat and Distribution | Physical
Characteristics | Senses | Behavior |
Diet and Eating Habits | Reproduction | Anatomy
and Physiology | Hydrodynamics |
Longevity and Causes of Death | Appendix:
Classification | Bibliography | Books for Young Readers
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