Age & Growth

Because sharks lack hard parts such as usable scales and otoliths, information on age and growth in sharks is derived from counts of opaque and translucent bands on vertebral centra or spines.

Vertebrae are collected through fishery-independent surveys, NOAA research cruises, recreational fisheries, and by observers on commercial fishing vessels.

Preparation of vertebrae for ageing involves several steps. First, excess tissue is removed from the centra using a scalpel and sodium hypochlorite solution. After cleaning, the vertebrae are stored in 95% isopropyl alcohol. To enhance visibility of growth bands, vertebrae can be cut in half sagittally or sliced at varying thicknesses. Sections can be stained with crystal violet, silver nitrate, or alizarin red to enhance the growth bands. Sections can also be left unstained. Opaque and translucent bands are counted by placing a section under a dissecting microscope interfaced with an image analysis system.

A wide variety of additional techniques have been used to estimate the age of sharks (See Cailliet et al. 1986. Indo-Pacific Fish Biology: Proceedings of the Second International Conference on Indo-Pacific Fishes. Eds. T. Uyeno, R. Arai, T. Taniuchi & K. Matsuura. p.345-360. Ichthyological Society of Japan, Tokyo.).

Hale and Lowe (In review. Hale, L. and Lowe, C. Age and growth of the round stingray, Urobatis halleri (Cooper), at Seal Beach, California. Journal of Fish Biology) have determined the age and growth of the round stingray Urobatis halleri from Seal Beach, Ca, using vertebral sections. Annual periodicity was validated from stingrays injected with oxytetracycline and maintained in captivity over a two year period. The parameters estimated by the von Bertalanffy growth model were L infinity= 348 mm for males and 251 mm for females and k = 0.06 yr-1 for males and 0.11 yr-1 for females. The age structure of the population consisted of mostly older, mature males and females. Age at maturity was estimated at 3.8 yrs for females and 3.75 yrs for males, and the maximum assessed age was 14 yrs old. Males were more numerous than females throughout the year; however, from May through September, females outnumbered males. Based on the seasonality and age structure of this population, round stingrays are likely aggregating at Seal Beach for reproductive purposes.

The Shark Population Assessment Group is currently conducting age and growth studies on several species, including the Atlantic angel shark Squatina dumerili, blacktip shark Carcharhinus limbatus, bull shark C. leucas, sandbar shark C. plumbeus, and scalloped hammerhead shark Sphyrna lewini. Results from previous age and growth studies can be found by clicking the Publications link on the right.