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tiger shark cape eleuthera study

Interesting Shark Study in the Bahamas

The Cape Eleuthera Institute’s Shark Research and Conservation program just published an interesting article detailing a single observation made in the Bahamas during one of their studies back in 2012.

ABSTRACT

Few data are available on interspecific elasmobranch interactions during predation events. This report describes and discusses empirical data from a single event in which four sharks (species: Carcharhinus leucas, Galeocerdo cuvier, Sphyrna mokarran and Carcharhinus perezi) competed for foraging opportunities on a fifth shark (C. perezi) caught on an experimental longline. Analysis of video footage suggested competition was enforced without agonistic behaviour and access to the resource was not governed by size. The singularity of the data set and the artificiality of the situation limit the strength of the conclusions. The rarity of such an observation warrants, however, a published description of the event to provide an example of the behaviour of apex predator interactions in the field.

While sampling sharks off South Eleuthera, the research team was using the gangion rig depicted here:

cape eleuthera shark fishing rig

In total, the study caught, sampled, and released 146 sharks, with the exception of one…the one this current publication is about. A Caribbean Reef Shark, Carcharhinus perezi, had just been hooked on the shark rig. For the next 90 minutes, a large Bull Shark, Carcharhinus leucas, circled the shark and eventually attacked and killed the shark. This predation event resulted in a Great Hammerhead (Sphyrna mokarran) and Tiger Shark (Galeocerdo cuvier) coming in to investigate. The entire event was caught on film and can be seen in this video:

 

While the great hammerhead was the largest of the three sharks, it only investigated the feeding opportunity briefly and seemed to be run off by the bull shark.  Once the tiger shark showed up, however, the bull shark – who was significantly larger – lost the opportunity to feed.  The tiger shark seemed to dominate every interaction it had with the other species, despite it’s smaller size.

The research group admits that complete interpretation of this single event, possibly swayed by the unnatural hooked condition of the reef shark, may be difficult.  It does show, however, a very interesting interaction between species and offers a very rare insight into this behavior.  Obviously, as the CEI group admits, replicating this to help better understand the interaction between species during predation would have some ethical issues.

To access the full text published paper, click here

Take a look at these interesting research articles:

Study says Marine Protected Areas can benefit large sharks

Prelim Research: North Carolina Attacks

Don’t bite the hand that feeds

SeaWorld announces end to captive orca whale breeding

NOAA 2015 Coastal Shark Survey

1916 shark hunt newspaper

1916 NJ Shark Attacks: The Aftermath

Did you miss the first article:  1916 Shark Attacks: The Real Jaws

As you can imagine, news of the string of attacks sparked mass hysteria, on a national level, although it was not immediate.  After the first incident, the state fish commissioner of Pennsylvania wrote in the Philadelphia Public Ledger:

Philadelphia Public Ledger

“Despite the death of Charles Vansant and the report that two sharks having been caught in that vicinity recently, I do not believe there is any reason why people should hesitate to go in swimming at the beaches for fear of man-eaters. The information in regard to the sharks is indefinite and I hardly believe that Vansant was bitten by a man-eater. Vansant was in the surf playing with a dog and it may be that a small shark had drifted in at high water, and was marooned by the tide. Being unable to move quickly and without food, he had come in to bite the dog and snapped at the man in passing.”

After the second incident however, the news made front page of major national newspapers including the Washington Post, San Francisco Chronicle, Chicago Sun-Times, and Boston Herald.   The result was an approximated $250K decline in tourism which amounts to over $5 million dollars at 2015 rates.  Resort towns enclosed their beaches with steel nets but that did little to reassure the public.

1916 shark hunt newspaperThe ensuing shark hunt was sanctioned by local governments all the way up to the federal level, in many cases offering significant rewards.  Hundreds of sharks were captured and killed along the east cost in what has been described as the greatest shark hunt in history.

Mystery remains whether there was a single rogue shark responsible for the string of attacks, or if there were several animals involved.  The two most likely culprits are the Great White Shark and the Bull Shark.  Many believe that a great white was responsible, but since the final attacks all occurred in Matawan creek miles from the ocean where salinity levels are low, others feel it had to be a bull shark.

On July 14th, 2016, just days after the final attacks, a shark that was later identified as a great white, was captured in Raritan Bay, just a few miles from Matawan Creek.  Michael Schleisser offered a heroic tale of the battle with the 7.5 foot shark, stating that it nearly sunk his boat before he was able to beat it to death with a broken oar.  After getting the shark back to shore, the animal was identified as a great white shark and the contents of it’s stomach included “suspicious fleshy material and bones,” later found to be human remains.  After this catch, there were no more attacks and the media proclaimed that the rogue shark had been killed.  The only surviving photo of that shark is from the Bronx Home News.1916 nj shark maneater

There is likely to be continued debate over the number of sharks and species responsible for the incident.  The International Shark Attack File officially reports the great white as the responsible shark.  It’s director, George Burgess states:

“The bull draws a lot of votes because the location, Matawan Creek, suggests brackish or fresh waters, a habitat that bulls frequent and whites avoid. However, our examination of the site reveals that the size of the “creek,” its depth, and salinity regime were closer to a marine embaymentand that a smallish white clearly could have wandered into the area. Since an appropriate sized white shark with human remains in its stomach was captured nearby shortly after the bites (and no further incidents occurred), it seems likely that this was the shark involved in at least the Matawan fatalities. The temporal and geographical sequence of the incidents also suggests that earlier bites may have involved the same shark.”

The incident, now nearly 100 years old, single handedly changed the nations attitude toward sharks.  Before the fatal shark attacks of 1916, it was not believed that sharks could or would attack healthy bathers near shore.  In fact, some felt it attacks were more likely the result of a large sea turtle.  Much has changed in public perception and scientific knowledge, and this incident had a major impact on that.

howard hall filming a bull shark

Bull Sharks – knows no bounds

Description

Bull shark, Carcharhinus leucas, from the CARCHARHINIDAE family. Depending on where you are in the world, you might also hear it referred to as a Ganges shark, Zambezi shark, ground shark, shovelnose, freshwater whaler, swan river whaler or slipway grey.

As its name suggests, a bull shark is large, stout and unpredictable. They are distinguished from other sharks by their stout appearance. Male bull sharks grow to an average size of 7 feet (2.5 m), whereas the females are bigger, with an average length of 11 feet (3.5 m). They weigh about 200 lb (90kg), 290lb (130 kg) respectively.

Bull sharks are wider and heavier than other requiem sharks of comparable length, and are grey on top and white below. The second dorsal fin is smaller than the first. The bull shark’s caudal fin is longer and lower than that of the larger sharks, and it has a small snout, as well as lacking an interdorsal ridge. This species reaches maturity at about 6 years and lives to be least 14 years.

Location

bull shark carcharhinus leucas

Range of the Bull Shark

They’ve been spotted as far north in the Atlantic as coastal Massachusetts and as far south as Brazil. In the Indian Ocean, you can find them from Africa and India to Vietnam and Australia. They tend to avoid the cold waters of the Pacific. They can be a common sight in big rivers. There have been reports of bull sharks as far as 1000 miles (1600km) down the Amazon. They were also sighted in the Mississippi. It’s one of only two species of shark that can live in freshwater — the other is the rare river shark.

The ability to be able to survive in both freshwater and saltwater also gives it a benefit that has been driven by evolution. Because the majority of sharks are only able to survive in saltwater, the bull shark has evolved to have their offspring in the fresh water where other sharks cannot enter. The fresh water acts as a protective area where the young are able to grow and mature without the threat of larger sharks preying on the younger bull sharks.

Diving with The Bull shark

Bull sharks like to dwell in shallow coastal waters (less than 100 feet in depth) , so you can be sure to encounter them more frequently, than say, an Oceanic whitetip. The fact that they are considered territorial animals assures that you are bound to catch one with your underwater camera. Bull sharks are a sight to behold and are a truly unforgettable experience for any scuba diving enthusiast.