Catch of the Day
Scientists find super rare river sharks hiding in plain sight at a Papua New Guinea fish market.
Everybody knows that sharks swim the salty expanses of the ocean. But in freshwater, you galeophobics have nothing to fear, right? Nope. Scientists recently rediscovered two species of river shark after analyzing the DNA from fish at a Papua New Guinea market. It’s the first time either the speartooth or the northern river shark has been officially seen since at least the 1970s, prompting scientists everywhere—O.K., fine, maybe just me—to wonder whether there’s hope for Jimmy Hoffa yet.
Not only does this news mean these species haven’t gone extinct, but it also reminds us that the world is bigger than it sometimes feels, with mysteries left to uncover. Sure, Google’s got every goldarned thing from Mount Everest to the Great Barrier Reef uploaded to the Cloud, but there are still waters so murky and remote that jaws like this can elude scientists for decades.
Did you get that? Scientists have never even seen this species, Glyphis glyphis, as grownups before. That’s how crazy-cryptic-cool they are.
River sharks can survive in freshwater—some of the only sharks able to do so—but they also dwell in salty coastal areas, like the brackish waters of estuaries.
They have beady little doll’s eyes, probably an adaptation to their often cloudy, sediment-filled habitat. As far as we know, river sharks eat prawns and fish, relying on electroreception to locate prey where visibility is as clear as mud.
White, a senior curator with Australia’s Commonwealth Scientific and Industrial Research Organization, explains how all river sharks in the Indo-Pacific are vastly understudied. Given their disappearing act, it’s no surprise that the two species have earned spots on the International Union for the Conservation of Nature Red List. The speartooth is endangered, while the northern river shark (G. garricki) is critically so. Neither enjoys any current protections under Papua New Guinea law.
These predators have been able to evade science for so long because they mostly occur in places that are difficult to get to—and downright impossible in which to set up a routine sampling operation.
The only easy place to search for them is local fish markets. Most sharks and rays, White explains, are caught accidentally by fishermen with gillnets aimed at bony fish such as barramundi. Even though sharks and rays aren’t the targets, everything hauled up in the nets gets taken ashore, either to be used for meat or bait. Fins are cut off, dried, and sold in local markets or exported to China and Taiwan as part of the shark-fin trade.
That’s why last November, White and his coauthors visited various markets in and around Daru, the capital city of Papua New Guinea’s Western Province. With the help of local chairmen, the scientists were able to obtain DNA samples from 66 dried caudal fins found for sale.
DNA results revealed that these fins represented a plethora of species, including lemon sharks, creek whalers, shark rays, and a crazy-looking type of hammerhead called the winghead shark, which is itself near threatened.
The speartooth fin was the most important finding buried in the pile—at first. When the scientists headed back to Australia, they left a camera with a local chairman named Jogara Page and told him to document any sharks brought to market in the nearby city of Katatai. Page came through—big time—by snapping pics of a nearly 3.5-foot northern river shark and two adult male speartooths, each more than 8.5 feet long. “It’s hard to believe an animal of that size has gone unnoticed for so long,” says White.
That these animals are still being caught regularly could be a sign that the populations are faring better than river sharks elsewhere in the world, says White. For instance, the possibility that the Ganges shark (Glyphis gangeticus), native to India, may still be out there is based entirely on photographs of a single jaw taken in 2001. Before that, you’d have to look back to 1867 to find another confirmed report.
Obviously, the fact these rare sharks are being bought and sold in fish markets does not bode well, but besides fishing, habitat degradation may also be taking a toll. The pollution and sedimentation from inland mining operations, for example, have a big effect on water quality downstream. Then again, White says that increased turbidity, or haziness, just may create more of the kind of habitat that river sharks thrive in.
We just don’t know much about these creatures. But at least now we know they exist on this planet that still retains many of its secrets.
Just think, the megamouth shark was only just discovered in 1976—and those suckers can grow up to 18 feet in length. Who knows what other awesomeness still lurks in the murk?
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