Age and Growth
Age and growth of the great hammerhead shark (Sphyrna mokarran)
Hammerhead shark populations have been severely depleted in recent years largely due to bycatch mortality in commercial long-line fishing. To better understand this decline, fisheries managers are developing species specific stock assessment models for sharks that have traditionally been managed as a species complex. Accurate life history data, particularly age and growth data, are needed to conduct these species specific stock assessments. Currently, there are no published age and growth studies on the great hammerhead shark in any part of its habitat range.To address this issue, FPSR scientists, in collaboration with scientists at NMFS Panama City lab, are conducting an age and growth study on S. mokarran. Specimens have been collected through both fishery-dependent and fishery-independent sampling programs. We determine the age of the sharks through analysis of the growth rings present on their vertebrae. After verifying the periodicity of growth band deposition, we can enumerate the growth bands to determine the age of the specimens. Comparing the age of the sharks to their lengths allow us to develop a growth model. This growth model will predict how fast these sharks can grow and to what theoretical maximum size. These data can then be incorporated into the stock assessments to develop more biologically meaningful conservation measures.