Chondrichthyes (cartilaginous fish, including sharks, rays and chaemeras) >

Size, age and growth

Most cartilaginous fishes are smaller than people. About 50% of living sharks reach a maximum total length of between 15 cm and 1 m long, and 82% reach two m or less, while 18% percent of the species reach over 2 m total length. The average maximum length for living sharks is about 1.5 m total length. Some 4% of the species of sharks are gigantic, 4 to 12 or more meters long. These include the largest fishes, the Whale and Basking sharks, which overlap the larger cetaceans in size; the basking shark may reach 12 m and the whale shark over 15 m long.

Most rays are less than 1 m long at maturity, and probably less than 10% of living rays exceed a width of 3 m or length of 4 m. The largest living rays include the sawfishes (Pristidae) 7.3 to 9.8 m long and mantas (family Mobulidae) 6 to 7 m wide.

In contrast, some sharks and rays are dwarves, mature at a length of 10 to 20 cm. The smallest sharks are dogfish (family Squalidae) and finback catsharks (Family Proscylliidae) about 15 cm. long at maturity; some electric rays are mature at only 10 cm long. Chimaeras are small to moderately large at maturity, and reach a maximum size of 0.5 to about 2 m long.

Most cartilaginous fishes are slow growing and long-lived, with some species requiring up to 20 years or more to reach adulthood and with a maximum age of 75 years. Much emphasis has been placed on determining age and growth of cartilaginous fishes in recent years due to the increase in fisheries exploitation of many species and its importance in managing such fisheries.

Age of cartilaginous fishes is usually estimated by counting bands across the vertebral centra or rings on the dorsal fin spines when present. These bands are usually enhanced by staining techniques, sectioning, or by radiographing (x-raying) them. Bands are then counted in much the same way tree rings are counted to estimate the ages of trees. However, verification of the periodicity of band deposition remains unknown for most species. Bands are assumed to be annual in many species, but this has been verified for only a few species, including the Lemon shark (Negaprion brevirostris), Leopard shark (Triakis semifaciata), and the Thornback skate (Raja clavata). Verification of the period of band deposition is usually done by injecting live fishes with tetracycline, an antibiotic which places an identifiable chemical `mark' on vertebrae or spines where new hard tissue is being deposited. Fishes are tagged and returned to the sea and when the fishes are recaptured after a year or more at liberty their vertebrae or spines can be examined for the tetracycline mark. The number of bands deposited after the mark was induced can then correlated with the time the fish was at liberty. Another technique is to compare the banding on the edge of vertebral centra or the dorsal spine base from fish caught sequentially during a year, which may enable one to estimate how long it takes to deposit one band from its increase in width.

Males of the Spotted spiny dogfish (Squalus acanthias) may require up to 14 years to mature, while females may take at least 20 years to mature. The Great white shark may take between 10 and 15 years to mature and has been estimated to reach a maximum age of at least 23 years based on a six meter female caught off Gans Bay in 1987. Other species for which age at maturity have been estimated include; Spinner shark (Carcharhinus brevipinna) 6 to 7 years for males, 7 to 8 years for females; Blacktip shark (Carcharhinus limbatus), 4 to 5 years for males, 7 to 8 years for females; Zambezi shark (Carcharhinus leucas), males 14 to 15 years for males, over 18 years for females; Silky shark (Carcharhinus falciformis), males 6 to 7 years, females 7 to 9 years; Tiger shark (Galeocerdo cuvier), 7 to 10 years for both sexes; Scalloped hammerhead (Sphyrna lewini), males 10 years, females up to 15 years; Thresher shark (Alopias vulpinus), 3 to 7 years for both sexes; Blue shark (Prionace glauca), 5 to 6 years for both sexes; Shortfin mako shark (Isurus oxyrinchus), a minimum of 7 to 8 years for both sexes.

Text by Leonard J.V. Compagno, David A. Ebert and Malcolm J. Smale 

  Iziko Museums of Cape Town, 2008

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