The last place you’d expect to see the folks from CSI sleuthing around is the bowl of soup you’re having for lunch — unless, of course, you’re having shark fin soup. In that case, you may be enabling an environmental crime, and now there’s DNA evidence that can give you away.
People who grew up on shark fin soup insist the stuff is sublime, and since there’s no accounting for what different cultures find delicious (anyone care for the boiled tongue of a domestic cow—with spicy mustard?) let’s stipulate that it’s as good as its loyalists say. But catching and finning sharks, then tossing them overboard so they can bleed to death is cruel by definition. What’s more, while the human appetite for shark fin soup seems to be unlimited, the supply of sharks themselves is anything but. By some estimates, global shark populations are down 90%. Worse, the animals breed extremely slowly; one species popular for its fin — the common dusky shark — enters its reproductive cycle only once every three years. Even if all fishing stopped today, it would take hundreds of years for their numbers to rebound.
Efforts are being made by conservationists around the world to ban the trade in shark fins or at least to monitor it — though nothing even remotely comprehensive or binding has ever been enacted. If nothing else however, it would help to know where sharks are being caught; that could at least alert one country if outside fishermen are poaching in its territorial waters, sparing the fish from being doubly plundered. Now, according to a pair of studies published in Endangered Species Research and Marine and Freshwater Research, it may be possible to use genetic testing to pinpoint the home waters of both dusky sharks and the equally popular copper sharks and provide at least those two species a measure of protection.
Both duskies and coppers are found in scattered populations around the world. The animals may prowl the deep oceans but the females always return to the coastal areas in which they were born to give birth — and all of their daughters will do the same. That keeps discrete populations anchored in discrete regions pretty much in perpetuity, and this can lead to DNA drift, so that a copper shark community in, say, the Gulf of Mexico would be genetically distinguishable from one off the coast of Japan, even if they were all still members of the same species. That, at least, is what the investigators behind the new papers hoped, and they decided to find out, sampling the genome of sharks as fishing boats in various regions returned with their catch. As they predicted, the DNA was indeed unique to the fishing grounds.
“By analyzing the genome that is inherited solely through the mother,” said lead researcher Demian Champan, a marine biologist at Stony Brook University, “we were able to detect differences between sharks living along different continents — in effect, their genetic zip codes.” Once you have the genetic profile of all the local species on record it would just be a matter of sampling a suspicious bowl of soup and seeing if you get a match.
OK, in a whole world of environmental hurt, no one’s likely to recruit a SWAT team of soup police anytime soon. But should the global community ever come together to stop or at least curb the slaughter of the sharks, random samplings of local fare would be one effective way to monitor compliance. Sharks may not be anybody’s favorite critter and there may even be some primal pleasure in seeing them reduced to nothing more than a menu item. But there is a limited window in which we can act before the problem simply resolves itself — but only because all of the sharks are gone.
