The ocean's warming could also play a role, some researchers say, because this change in temperature affects where sharks' prey are swimming at certain times of the year. In fact, new research suggests that if climate change increases temperatures in Antarctic waters to just above freezing year-round by the end of the century, as some models predict, sharks may show up there for the first time in 40 million years. While they may shift their distribution, this doesn't mean shark numbers are destined to grow. In fact, carbon emissions are making the sea more acidic, which could decimate species on the lower end of the food chain and deprive sharks of the midlevel predators they need to consume.
While we might be alarmed at any indication that sharks are showing up in different places or biting into more and more humans, they're far more vulnerable to us than we are to them. There have been only two recorded shark attacks in Massachusetts waters since 1670, but commercial fishing has decimated the area's spiny dogfish shark population in recent decades. Since the 1970s, the numbers of scalloped hammerhead and tiger sharks have fallen by 97 percent along the U.S. East Coast, with bull, dusky, and smooth hammerhead sharks declining by as much as 99 percent. In the Mediterranean Sea, researcher Francesco Ferretti and his colleagues found that fishing has decimated large, predatory sharks over the past two centuries. Looking at the activities of the 21 countries that use the Mediterranean as their fishing grounds, they concluded the species that fared the best, blue sharks, declined 96 percent during that time, while hammerhead sharks declined more than 99 percent.
Elizabeth Griffin Wilson, marine scientist and fisheries campaign manager for the advocacy group Oceana, said that it's actually striking that there aren't more reports of shark attacks. "As human population grows and as we spend more time in the ocean, chances of interaction with sharks increases," she told me. "And we would expect this increase in interaction to be more dramatic than it has been, and one of the primary reasons it has not been more dramatic is because shark populations are depleted."
The International Union for Conservation of Nature estimates that as many as a third of shark species now face the danger of extinction. Although part of this depletion is unintentional -- sharks frequently get caught on fishing lines set for tuna and swordfish, two lucrative global fisheries -- vessels bring in tens of millions of sharks each year to supply the growing shark fin soup trade in Asia.
While tasteless, the gelatinous noodles extracted from sharks' fins are the essential ingredient in a high-priced delicacy that connotes status in Chinese society. It defines whether a wedding banquet is considered elegant, provides a boost for business executives hoping to impress their clients, and has become increasingly popular as per capita incomes in China and other Asian countries have risen.
As with underwater attacks, sales of shark fin soup in a given country provides a good indication of both its economic and demographic prospects. Shark fin consumption in Singapore more than doubled between 2006 and 2007, according to data analyzed by the Straits Times, despite a price increase of 30 percent between 2003 and 2007. Two factors drove this increase: Singapore's economy grew in 2007 after a slump, and nearly 24,000 couples got married that year, the highest number registered in the country since 1999.