Bull sharks trade the seven seas for Ol’ Man River.
Of the things you might expect to encounter in the Potomac River, here’s one you may not have thought of: 8-foot sharks. Which is why the discovery last summer, of not one, but two 8-foot bull sharks trapped in a commercial fisherman’s net on the Maryland side of the Potomac caused something of a splash—so to speak—in the local news. What gave the story a particular twist was that the same fisherman had made the news three years earlier—for catching a bull shark in his net on the Potomac. In that same week in 2010, another fisherman on the river also caught one.
“Cue the Jaws theme,” read the 2010 headline on The Washington Post’s breaking-news blog.
The casual reader, skimming articles about both events, might note that the catches took place near where the river meets the Chesapeake Bay and conclude that “sharks in the river” is the stuff of low-budget fright films. The casual reader would be mistaken.
“I often like to say that almost everything you know about sharks is wrong,” says John Morrissey, a former professor of biology at Sweet Briar College in Amherst and a man who knows his way around a shark. (He may be the only person you’ll ever talk with whose story about being pursued to the beach by a hungry tiger shark ends with him angrily storming back into the water, armed only with mask and fins, to try to chase the shark down and teach it a lesson.)
So, a few true things about sharks: They come in all sizes, most of them pose no danger whatsoever to humans and not all of them have to keep moving or die. And one more thing: If you think what you know about sharks is that they only live in the ocean, then meet the bull shark. Its general territory, yes, is warm, shallow, near-coastal ocean waters. But the bull shark can also comfortably inhabit fresh water, one of only two shark species (the other is the rare river shark) known to have this capability. As a result, the bull shark can—and does—travel up rivers. Bull sharks have been spotted more than 2,000 miles up the Amazon, for example. They are found in the Ganges in India and the Zambezi in Africa. And if you prefer your excitement closer to home, consider that a bull shark has been caught more than 1,500 miles up the Mississippi.
According to Morrissey, it was once believed that the bull sharks found in the world’s various rivers each represented a unique species. The same theory held true for the bull sharks even more surprisingly found in the vast, landlocked Lake Nicaragua; it was assumed that these sharks were an isolated freshwater species. Tagging, however, proved this theory wrong and led to the astonishing confirmation that these large sharks manage to move between lake and sea, swimming, salmon-like, some 120 miles up Nicaragua’s fast-moving, rapids-strewn San Juan River. One imagines six or seven feet of Carcharhinus leucas leaping through a white-water passage; that, indeed, would be a sight to give a person pause.
Here in Virginia, we probably don’t have too much occasion to keep double-checking for dorsal fins in the James. Morrissey notes that the bull shark is not common in our waters, preferring tropical and subtropical regions (a preference that, following this past winter, quite a few Virginians likely share). However, in the warmer mid- to late-summer months, the bull shark’s range can extend as far north as Massachusetts, and in our area, you might think of bull sharks as something like summer people with a house on the Bay.
Summer people who are 8-foot carnivores, however, do tend to garner more attention than the average out-of-towner, and often, articles about the bull shark go in for an array of alarming adjectives: aggressive, deadly, dangerous. It is true that the bull shark, along with the tiger and great white, belongs to an exclusive fraternity of three considered responsible for the majority of shark attacks upon humans. That said, the main reason for this may simply be a matter of proximity. Bull sharks particularly frequent turbid, low-visibility, near-shore waters—you know, like the ones you find at the beach? Yet despite the ever-growing number of people flocking to the shore and splashing about, shark attacks by all species, including the bull shark, remain rare. “Sharks bite about 100 people a year,” notes Morrissey, pointing out that you put yourself at far greater risk getting into the car to drive to the beach than you do getting in the water. And if you’re keeping count, in the matter of us vs. them, it’s not the fish who are winning: as a statistic from the National Geographic Channel notes, for every human killed by a shark, about two million sharks are killed by humans.
Still, for reasons that still need explaining—perhaps even as a necessary part of their life cycle?—bull sharks may decide to head upstream this summer for a swim. A long swim. A very, very long swim. Watch your toes, Huck Finn.
Although bull shark populations are not considered to be under serious threat (yet), these sharks take years to reach sexual maturity. The females give birth to from one to as many as 13 live-born, free-swimming pups, which are born with a placenta and umbilical cord attached. A fascinating thing about sharks is illustrated thereby: their remarkable self-healing abilities. The umbilical scar, which on you and me means a belly button for a lifetime, on a bull shark will not only heal but in time disappear altogether.
The young sharks, which are about two feet long at birth, spend some time sheltering in the low-salinity shallow waters of bays and estuaries and the like, where they are reasonably safe from the bigger sharks, including occasionally their own species, that might be inclined to eat them.
And then at some point, for reasons that still need explaining—perhaps even as a necessary part of their life cycle?—they may decide to head upstream for a swim. A long swim. A very, very long swim. Watch your toes, Huck Finn.