Australia Hatches Plan to Save Gray Nurse Shark
Monday, March 27, 2006
From snout to tail they can be 10 feet long, silver-gray torpedoes of pure muscle with dorsal fins that slice ominously through placid coastal waters.
Their hideously long teeth, which curve inward like sabers, regenerate from scratch every two weeks -- the better to pierce their hapless prey.
And if all goes well, scientists will soon be growing these creatures by the dozens in artificial wombs, to be released among the swimmers and scuba divers off Australia's east coast.
The animals at the core of this seemingly gruesome venture are gray nurse sharks -- some of the meanest-looking, most endangered and, as it turns out, most mild-mannered sharks in the world.
Known among divers as the "Labradors of the sea," gray nurse sharks are "the perfect shark," says Robert Harcourt of Macquarie University in Sydney. They are huge. Their eyes are pitiless. And they swim with their mouths open, revealing those menacing thickets of dentition.
"They'll come right up to you" -- an act of seeming aggression sure to make a diver's heart thump like the bass-fiddle thrumming in the movie "Jaws" -- "then they'll turn around and just leave you alone," Harcourt said. "They're gentle as puppy dogs."
All the thrill and none of the risk. What more could a neoprene-clad tourist hope for?
Unfortunately, after decades of having been hooked, netted and spear-hunted -- in large part because of a misconception that they are man-eaters -- this docile species that feeds on fish, crabs and lobsters is now struggling for survival in the handful of coastal areas where it survives.
Off the U.S. East Coast, where they are called sand tigers and are listed as "vulnerable" (one level shy of "endangered"), their numbers have failed to rebound despite protections enacted 10 years ago. Off the east coast of Australia, where Harcourt works, Carcharias taurus is "critically endangered," with as few as 300 individuals remaining where many thousands once roamed.
New research published earlier this month brought home just how endangered Eastern Australia's gray nurse shark population really is. Harcourt, Macquarie colleague Adam Stow and others obtained tissue samples from 65 of the sharks off Australia's east and west coasts and off the east coast of South Africa. The samples, which came from animals that had died in nets or had been captured briefly for the purpose of tagging them, allowed the team to compare individuals' gene sequences.
Those DNA studies showed that there is no intermingling among the eastern Australian population and the other two, which means the critically endangered eastern group has no hope of being replenished by individuals from the other regions.
Equally worrisome, the studies showed that the members of the eastern Australian population are extremely inbred, a situation that may make them especially susceptible to disease or disaster.
"Given the ongoing population declines of C. taurus in eastern Australia and negligible migration among Australian populations, extinction is imminent in east Australian waters without urgent conservation efforts," the team concluded in the March 1 online edition of Biology Letters, published by the Royal Society.
As the top predator in its environment, the gray nurse shark is crucial to maintaining ecological stability in the regions in which it lives. But a quirk in the species' reproductive biology makes it difficult for the creatures to rebuild their numbers.
Females have two separate uteruses, with each womb serving as home to as many as 20 fertilized eggs. It's a picture of great fecundity, and a litter of 40 would be a blessing. But life inside a gray nurse womb is not that simple.
Soon after developing their primordial jaws and teeth, and while still about four inches long, the gill-slitted fetuses attack each other in what shark biologist Nick Otway calls a "battle royal" of sibling cannibalism. The mayhem ends with just two surviving offspring -- one in each uterus.
Otway, who works with the New South Wales Department of Primary Industries, which oversees that state's fisheries programs, foresees a braver and newer way to make gray nurse sharks: artificial wombs, each big enough to hold a three-foot-long baby, which is how big gray nurses are at birth.
The idea is to use endoscopic surgical tools to remove dozens of embryos from pregnant females -- including some inseminated with sperm from distant males to boost genetic diversity -- then give each embryo its own fluid-filled, climate-controlled tank to grow in.
With government seed money of about $350,000 a year, Otway's team is now designing a prototype. Otway also is gathering data on ideal temperatures, nutrient levels and waste removal parameters to support gray nurse shark gestation.
The approach is radical. But Otway said it is better than the alternative of importing live females from other parts of the world. That would pose serious health risks to the translocated females, and could introduce new and potentially catastrophic diseases. Moreover, because gray nurse sharks give birth just once every two years, it would take a lot of imported females to boost population levels overall.
Not everyone is a fan of the shark womb plan. But more than opposing the project itself, dissenters fear the new focus could undermine government commitments to protect gray nurse shark habitat.
Australia has already designated several protected areas off its coasts. But powerful political forces aligned with the fishing industry have kept some of those areas open to fishing, which has led to a slow but steady stream of inadvertent shark catches and deaths. Many marine conservationists have been fighting to strengthen fishing restrictions.
Andy Davis, a marine ecologist at the University of Wollongong in New South Wales, warned that the 10 years it could take to get offspring from the artificial womb program is longer than the eastern population is expected to survive, according to some extinction estimates. "Offering them protection in sanctuary zones in appropriate habitat offers them their best chance of survival, in my view," Davis said.
Lizzie Bowman of the Humane Society International in Sydney agreed. "We are not opposed" to the artificial womb project, Bowman said in an e-mail. "It's just that we don't see the point in it unless the threats to the species in their habitat are addressed."