Vieillir un poisson requin en comptant les anneaux de croissance formés sur la vertèbre et cette photo montre le cartilage de la colonne vertébrale et les anneaux
5184 x 3455 px | 43,9 x 29,3 cm | 17,3 x 11,5 inches | 300dpi
Date de la prise de vue:
26 août 2012
Lieu:
Canada
Informations supplémentaires:
The age of a shark is determined by counting the growth rings formed on the vertebra. The vertebral rings are laid down on a yearly basis not unlike those of trees. This method is analogous to the method used in ageing bony fish using the otolith (earstone), although not as well refined. However, sharks do not have otoliths, necessitating the use of the vertebrae. This vertebra is from a Blue Shark. The age of sharks can be estimated using either the vertebral centra (the spindle-shaped central part of fish vertebrae), and the dorsal fin spines, if they have any. In either case, these elements are sectioned transversally and stained, to make the internal banding pattern evident. This banding pattern is produced by the seasonal deposition of calcified tissues during the growth of the animal. Usually, the researchers use the band counts from animals of known ages to calibrate the age estimations of other individuals. Each species has their own particularities with respect to their growth pattern, and most continue to grow while they live (although at a slower rate when they're older). Because of this, it's impossible to know the age of a wild specimen. The current record indicates that a whale shark (Rhiniodon typus) lived for 70 years, and a spur dogfish (Squalus acanthias) lived for 60 years
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