Bull Sharks (Carcharhinus leuceus) in Fresh Water Rivers

Not long ago, Noel Todd caught an 8 foot long, 368 pound bull shark in Shell Creek which is located in Valona, Georgia.  Shell Creek is a brackish stream not far from the coast, so it’s not shocking that a shark  might be found here.  However, bull sharks have been sighted 2500 miles up the Amazon River.  The North American inland shark-catching record was set in 1937 when 2 fishermen caught a bull shark in the Mississippi River next to Alton, Illinois.

“Nearly comatose” bull shark discovered in Lake Pepin, Minnesota which is connected to the Mississippi River.  This is the lake where Laura Ingalls’ father (of Little House on the Prairie fame) used to fish.  Bull sharks are tropical to semi-tropical species, not well adapted to such cold waters.  I discovered 15 months after posting my article that this photo is an APRIL FOOLS JOKE.  I was fooled and I apologize to my readers.

The bull shark that Noel Todd caught in Valona, Georgia in a  brackish water tidal inlet.

In Georgia before the dam that created Lake Seminole was built, bull sharks used to congregate in the Chattahoochee River adjacent to a beef processing plant above Albany where the factory dumped the offal into the water.  Bull sharks are common in 2 freshwater lakes that have access to an oceanic outlet–Lake Nicaragua in Central America and Lake Pontchartrain, Louisiana.

Unlike most species of sharks, bull sharks are capable of living in freshwater because their kidneys with the aid of a special gland help them retain salt.  Most other species of sharks don’t have the physiology to be able to withstand long exposure to freshwater.  Other species of sharks would suffer cell edema if trapped in freshwater, and they would die.  The ability to survive in freshwater gives bull sharks a tremendous advantage over other shark species.  Bull sharks are a shallow water species that live in coastal waters.  The females give birth to 1-13 live pups which often travel to freshwater rivers where they immediately become a top predator.  Instead of being vulnerable prey like most juvenile marine life, they top the food chain.  They simultaneously avoid predators, while gaining access to a bounty of prey items.  This may also help them avoid cannabilistic adults of their own kind.  Most of the young pups stay in brackish waters and return to the ocean when they grow larger.  Scientists don’t know why a few swim great distances up freshwater rivers, but I believe that behavior is influenced by a random mutation that could potentially lead to a beneficial adaptation.

Bull sharks account for more attacks on man than any other shark species, probably because they’re a coastal species more likely to come into contact with people.  It was probably this species that inspired Peter Benchley to write Jaws. Five shark attacks that occurred along the New Jersey coast in 1916 provided the plotline for his classic story.  Two of the shark attacks occurred in Matewan Creek–16 miles inland. 

Bull sharks get their name from their habit of attacking and eating other sharks, making them a bully among sharks.  They also feed upon fish, rays, shrimp, crabs, sea snails, turtles, carrion, and garbage.  They’re considered a near threatened species which is not surprising since the entire ocean has pretty much been overfished.

Bull sharks are not the only primarily salt water species of fish found way up freshwater rivers.  Flounder, hogchokers, mullet, tarpon, and needlefish expand their range from brackish water and swim into the freshwater of the middle Savannah River basin every summer.  I’ve never had the opportunity to fish in a brackish segment of the a river but it must be interesting.  Largemouth bass, gar, and catfish are common freshwater species found in brackish waters where they swim alongside bullsharks, mullets, and flounder.

Hog chokers, a type of flounder, swim into the middle Savannah River every summer.

Needlefish–another saltwater species that spends summer vacations in the middle portion of Georgia’s freshwater rivers.

Mullet–a great tasting meaty fish that schools up freshwater rivers.  I used to catch these with a cast net in the ocean off Harbor Island, South Carolina.

The pristine waters of the Pleistocene must have held exponentially more fish then those of today, but modern day damming, overfishing, and pollution have decimated fish populations.  Bull sharks likely swam way up freshwater rivers during the Pleistocene, but the odds of finding a fossil bull shark’s tooth hundreds of miles inland must be very low.  Bull shark’s teeth have been found at the Pleistocene-aged Isle of Hope site but this is on the coast in Chatham County.

Panthera atrox! What Kind of Cat was it?

One of the biggest cats to ever stalk the world roamed across North America during the Pleistocene.  Panthera atrox, weighing up to 500 pounds and possibly more, was a giant in the genus that includes lions, tigers, jaguars, and leopards.  It fed upon the bison and horses and camels that grazed the Ice Age grasslands and woodlands.  Atrox is a Latin word, meaning cruel, though it’s an error for humans to attach our emotions to an animal that merely did what it needed to do to survive.  Nevertheless, I pity any poor animal caught in the clutches of this powerful predator.

The first fossil specimen of this species was discovered in Mississippi in 1850, and its discovery immediately caused scientific controversy.  Some thought the skull resembled that of a tiger; others thought it was a lion’s skull.  By 1930 scientists had learned how to determine the difference between lion and tiger skulls.  It seems the sutures on the foreheads of the two species are quite different.  Moreover, tigers have noticeably longer nasals.  And from a view of the top of the skull, lion nostrils are visible because their skulls are more elongated, whereas those of the tiger can’t be seen from that angle.  Because Panthera atrox‘s skull closely resembled that of the lion, scientists determined that’s what it was.  Now, a new study using statistics based on data from detailed measurements of lion, tiger, jaguar, and atrox skulls and jaws, has upended the line of reasoning that assumed Panthera atrox was a lion.

The jaw bone of Panthera atrox most closely matches that of the jaguar, though it’s not an exact match, just like the skull of atrox most closely resembles that of the lion but is larger and more elongate in shape, and so is not an exact match of that species either.  So what was it?  The authors of the study referenced below measured every part of the skulls and jaws from 23 atrox fossils, 78 tigers, 126 lions, and 57 jaguars.  They then did a statistical analysis of the results and found that despite deviations between individual specimens of each species, all the measurements clustered into 4 groups, corresponding to each of the 4 species–strong evidence that Panthera atrox was indeed a distinct species.

Though this study surprises me, it makes sense because fossils of Panthera atrox are on average consistently 25% larger than anatomical specimens from extant lions.

Fossils of Panthera atrox are relatively common in western fossil sites, but they’ve also been found in Florida, and South Carolina in addition to the original type specimen discovered in Mississippi.  Undoubtedly, it occurred in Georgia.  True lions did live north of the ice sheet in what today is Alaska, but jaguars and Panthera atrox never advanced above the Cordilleran and Laurentide glaciers that covered what is now Canada.

The scientists who authored this recent study conclude that both Panthera atrox and jaguars descended from a Pliocene-age cat known as Panthera gombaszoengis which is sometimes referred to as a Eurasian jaguar.  This species colonized North America at the beginning of the Pliocene and different populations split into different species: some inhabiting forests evolved into jaguars, same living in open prairies evolved into Panthera atrox, which heretofore on this blog, I’ll refer to as the giant panther.

I believe genetic studies will eventually support this study.

The giant panther had a larger brain than lions and probably was more intelligent, making them a successful large predator, able to kill large game without the help of others of their species.

Because the giant panther is not as closely related to lions as formerly thought, it’s unlikely to have lived in prides.  Instead, like the vast majority of cat species, it survived as a solitary predator and competed with dire wolves and saber-tooths over the many large ungulate species then extant.  Throw in the mighty scavenging short-faced bear (Arctodus simus) and battles galore must have been the norm during Pleistocene dinnertimes.

Reference:

Christiansen, Per; and John Harris

“Craniomandibular morphology and phylogenetic affinities of Panthera atrox: Implications for evolution and paliobiology of the lion lineage.”

Journal of Vertebrate Zoology 29 (3) 934-945 September 2009

Note: Perhaps the giant panther looked like these jaguar/lion hybrids, though I guess they had a tawny coat, possibly lightly spotted.

www.bearcreeksanctuary.com/jaglions.htm