Shark Ageing

Biologists age sharks by counting the concentric calcified bands in x-rays of cross sections of the shark's vertebra, much like foresters count the rings in cross sections of a tree trunk. Researchers from the SWFSC Large Pelagics Lab studied the centrum growth-band deposition of vertebrae obtained from tag-recaptured shortfin mako sharks (Isurus oxyrinchus) marked with oxytetracycline (OTC). Tetracycline deposits where new calcification is occurring at the time of injection and makes a fluorescent time mark in the vertebrae that can be examined in relation to new vertebral growth when a fish is recaptured a year or more after injection and release. Sharks were tagged off Southern California from 1996 to 2010 and at time of tagging, oxytetracycline (OTC) was injected into their vertebrae. Upon recapture, to elucidate the vertebral bands, "hard" (high-frequency) X-radiography was used. X-radiography uses industrial, fine-grain, high-contrast film for sharpness and sensitivity to visually count vertebrate deposition bands. Two separate band counts were made: total band pairs (bands distal to the presumed birth band) and band pairs distal to the OTC mark. Their studies of OTC-marked vertebrae indicated that 2 band pairs are deposited each year. Tetracycline marking and release of tagged juvenile makos and juvenile and subadult threshers off California has verified the timing of 'annual' ring formation. 

Read their published work here: Wells, R. J. D., Smith, S. E., Kohin, S., Freund, E., Spear, N., and Ramon, D. A. (2013). Age validation of juvenile shortfin mako (Isurus oxyrinchus) tagged and marked with oxytetracycline off southern California. Fishery Bulletin 111, 147–160. doi:10.7755/FB.111.2.3

Shark vertebrae examined by X-radiography            Shortfin mako shark (Isurus oxyrinchus) aboard a SWFSC tagging survey     Shark vertebrae examined by X-radiography

Ageing studies are also underway to determine age and growth of shortfin mako shark sampled by Japanese longline from widely distributed localities in the Pacific, and the common thresher shark from the California-Oregon drift net fishery. The purpose of the mako ageing project is to help clarify movements of and effects of high seas exploitation on different mako age groups. They also hope to resolve existing problems in interpreting the timing of the formation of these calcified rings. This is a joint study between scientists from the Japanese National Research Institute of Far Seas Fisheries at Shimizu, Japan, and scientists within the Fisheries Resources Division at La Jolla, CA to independently age a sample of about 250 subadults and adults mako sharks from the western and central north Pacific.

See how NOAA researchers from the Northeast Fisheries Science Center conduct the same ageing studies:

NOAA Video: Ageing Sharks

NOAA Video: Ageing Sharks The previous link is a link to Non-Federal government web site. Click to review NOAA Fisheries disclaimer

Last modified: 12/8/2015