Despite Growing Fears, Sharks Are Integral To Coastal Ecosystem

Jun 19, 2015

measuring an Atlantic sharpnose shark - Rhizoprionodon terraenovae
Credit E. Woodward/ UNC Institute of Marine Sciences.

Recent events have led to an interest in the 50 shark species that call our coast home.  This week on the Down East Journal, we speak with Assistant Professor at the Institute of Marine Sciences Dr. Joel Fodrie about how this apex predator is actually an integral part of the coastal ecosystem.  

Fortunately, dangerous interactions between humans and sharks are extremely rare.  The fact that three unprovoked shark attacks have happened along our coast within days of each other is also very unusual.   Now, many beachgoers are scared to enter the water.

“People don’t focus on the odds, the odds are really, really low that there will be a bite.  People focus on the stakes and the stakes are really high.”

Dr. Joel Fodrie is the Assistant Professor at the University of North Carolina’s Institute of Marine Sciences in Morehead City. According to data from the International Shark Attack File from the Florida Museum of Natural History, there have been 55 shark attacks in North Carolina in the past 80 years, three of which were fatal.  The majority of attacks occurred in New Hanover, Onslow and Carteret counties.  Dr. Fodrie emphasizes that number is remarkably low when you consider the abundance of sharks found along the coast.

“Last week, people were in the water with sharks.  And, this week, if you’re in the water, there’s probably a shark somewhere within a few football fields.  And that will be the case next month and next year. And the incredible, vast majority of the time, the sharks are not cuing in on factors that lead to a bite.”

North Carolina is located at a breakpoint between northern and southern fauna.  The diversity of environments and water temperatures is conducive for supporting more than 50 species of sharks off our coast.  Researchers with the Institute of Marine Sciences study a variety of sharks, including twenty species that are fairly common in estuarine and near-shore waters.

"Many people have probably heard of the spiny dogfish fishery, that’s a common shark in North Carolina.  But we also have a lot of sharp nose sharks. The long term survey that IMS does has captured on the order of 6,000 to 7,000 sharks and about half of those are sharp nose sharks.”

Smaller sharks like Black tip, smoothhound and bonnethead sharks are found in the Core and Pamlico Sounds.

“A lot of the species we have here in North Carolina are typically 3-5 feet long. And that’s many of the species we tend to see more commonly.”

hammerhead shark
Credit E. Woodward/ UNC Institute of Marine Sciences.

Larger sharks are out there though, like the nurse, hammerhead, dusky and great white sharks.  It’s not known for sure what species of shark was involved in the attacks in Oak Island this past weekend.  But out of the dozens of species that patrol North Carolina’s coastline, Dr. Fodrie says only a handful of sizable sharks would be bold enough to swim into shallow water.

“The shark or sharks involved were estimated to be on the order of eight foot long. And that does perhaps narrow the playing field down some.  If you’re talking about an eight foot shark or nine foot long shark, it does sort of shift the balance towards a bull shark even perhaps a tiger shark.”

Dr. Fodrie says he’s personally seen two tiger sharks in waist deep water. Tiger sharks can grow to a considerable size - up to 18 feet – and are one of the most potentially dangerous species.  Another aggressive and common species found off the coast of North Carolina, in estuaries and even freshwater rivers is the bull shark.  While these species have been known to bite humans, Dr. Fodrie believes a number of factors led to the incidents last week.

“The water wasn’t very clear, there was lots of bait in the water.  There may have been fishing and chumming in the area.  Lots of people.  And so what you may have seen is that the conditions were ripe where there were multiple bites because that very rare combination of factors converged.” 

With the recent shark attacks, it’s reasonable that some beachgoers are hesitant to go in the water.  However, these apex predators of the sound and sea bring balance to the ecosystem. 

“Their role is to maintain and control populations of fishes and crustaceans underneath them.  They remove mostly the sick and weaker animals within a population. And also an indicator of ecosystem health. So if the ecosystem is functioning properly, there will be enough food and trophic transfer for it to support the shark population.  So they’re both a canary in the mine shaft and also a driver of a well-functioning system.”

Gray Redding is a technician working in the Fodrie Lab at UNC IMS.
Credit E. Woodward/ UNC Institute of Marine Sciences.

Sharks are the primary consumers of larger animals like turtles, fish and cow nose rays.  And since rays eat scallops, it’s important to keep their populations in check.

"The fewer the number of rays, the healthier the scallop population will be.  And that has historically been a very important fishery in North Carolina.  But as we’ve lost a lot of sharks, there’s a hypothesis that’s allowed the rays to expand in numbers, and therefore we’ve perhaps lost the scallop fishery.”

Another example of sharks bringing equilibrium to the ecosystem is by controlling the number of sea turtles and fish that consume coastal vegetation.

“We all tend to believe that sea grass is a really important habitat for producing commercially and recreationally valuable fishes, it’s a nursery habitat.  To some degree, sharks are really important to maintaining a balance between those plants and the herbivores that eat those plants.”

To better understand the movements of sharks, Dr. Fodrie is currently involved with a collaborative research project with Dr. Jeb Byers at the University of Georgia to study bonnethead sharks in Georgia.

“we put these little acoustic tags on sharks so that we can track them around fairly precisely in terms of the spatial resolution of our tracking to understand how long they’re in a certain marsh creek within a certain sound.”

bonnetthead shark
Credit E. Woodward/ UNC Institute of Marine Sciences.

This will give scientists a clearer picture on how bonnethead sharks respond to changes in habitat or fishing pressure and how much of an impact their feeding has on an ecosystem.

"If they’re in the area for a long period of time, their ability to impact blue crabs or smaller fishes may be different than if they’re very transient, and just passing through for only a short while.”

The team hopes to tag bonnetheads here in North Carolina later this summer. 

It’s important to keep in mind that the United States averages just 19 shark attacks each year and one shark-attack fatality every two years. A far more dangerous scenario involves land based lightning strikes which kill more than 37 people each year.

“Most of the time, sharks are trying to do three things, they’re trying to find food, they’re trying to reduce their risk from any predators they perceive, and at some point, they’re trying to reproduce.  And so they’re going to go to areas where one of those three things can happen.”

To stay safe, Dr. Fodrie says there are some things you should take into consideration when taking a beach swim.

“If you know there’s a lot of bait in the water be it swimming around, live, natural bait or bait from lots of fishing, bycatch, discards, those are factors that may draw in sharks.”

Practice swimming in groups instead of alone, refrain from excessive splashing, and don’t enter the water if you are bleeding.  Avoid swimming when water is murky. And remember, early morning and evening are prime feeding time for sharks.  More tips are available at http://ncseagrant.ncsu.edu/ncseagrant_docs/products/2000s/shark_sense.pdf