Posts Tagged ‘Minnehaha Creek’

Bull Sharks (Carcharhinus leuceus) in Fresh Water Rivers

August 29, 2012

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.

Lapshark?

“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.