Marine biologist and conservationist Neil Hammerschlag has an informative page on his website about current threats to shark populations and what you can to help. 

Neil writes, ”Shark populations are particularly vulnerable to this exploitation due to inherent life history characteristics which feature a pattern of slow growth, late maturity, long gestation, low fecundity (reproductive output) and long life, resulting in a slow intrinsic rate of population increase… In the Atlantic alone, shark populations have decreased between 60 and 90 percent depending on species, in just the last 15 years!”