Shark Week with marine biologist Andy Dehart

Aug 04, 2010

Andy Dehart, marine biologist and shark advisor to Discovery Channel's Shark Week, will be online Wednesday, Aug. 4, at Noon ET to discuss the series, swimming with sharks, conservation and, of course, shark attacks.

Hello all anxious to answer some of your questions about sharks. 

We're off to Cape Cod next week. Should we go swimming at the beaches? Any area in particular to avoid?

Certainly be mindful of the lifeguards advice on what beaches are safe.  They are being cautious with these sightings for good reason just as park rangers in our national forests are with bear sightings.  As long as there are not a lot of seals in the area there is really very little to worry about.

Is it true that we are not really that tasty to sharks and then when they bite us, they usually spit us out?

Yes in a strong majority of shark attack cases the shark leaves after the first bite realizing it did not get what it thought it was going after.

I've not seen a lot of Shark Week over the years, partially because whenever I turn it on, it's about someone getting bitten. Do you feel Shark Week does much to benefit sharks or, like Jaws, gives people the wrong idea of them?

If you look at Shark Week over the years there has been a mix of all types of shows form true natural history pieces to attack focused shows.  Viewers come to the shows for a variety of reasons.  Some are morbidly fascinated with attacks and we can not ignore that attacks do happen from time to time as they do with all large predators.  Others come in awe of the sharks.  The hope is that when they tune in they learn more about sharks and might care a little bit more about them.  Discovery runs shark conservation public service announcements every episode and has a great conservation portal on their website.

The reality is that sharks are hunted for their fins because they are worth and amazing amount of money.  They are not out there hunting them because they fear them.  In fact I think we have come a long way since the movie Jaws with the recent great white sightings in Massachusetts.  25 years ago every fisherman in town would have been out with harpoons to kill them and now we are studying them.  Part of that change in culture has been due to television programing but also public aquariums and more research on sharks.

Do you have a pet shark?

Most sharks do not make good pets.  In fact there are very few species that remain small enough to be housed in a home aquarium.  Unfortunately people still buy nurse sharks and other big sharks and end up calling public aquariums to get rid of them when they get to big.

I get my shark encounters enough at work at the aquarium and while in the field and do not feel they are well suited for the home aquarium unless the person has a great deal of experience and a very large aquarium.

Are sharks color blind

In fact most shark species do have color vision.  We know this from the presence of both rods and cones in the eyes.

Mr. Dehart, thanks for taking my question. Do you think sitting on a slippery, half-eaten whale carcass, as shown in a Shark Week program the other night, to get a photo of sharks feasting on it is responsible science, or is it reckless risk-taking that doesn't advance our knowledge of sharks, but looks good for the cameras? Also, why do sharks breach when chasing sea lions?

Rocky Strong who was the one that was standing on the whale is a very well known shark scientist who was one of my mentors when I was younger.  Not being on location when that show was filmed I can not say why he did this, but I do know he is a great shark photographer and was getting some amazing photographs and was comfortable with his abilities to be in the water with great whites if he fell off.  Being with great whites without a cage has been done by shark experts of which I consider Rocky.

As far as the breaching.  This behavior is fairly unique to S. Africa due to its bottom topography.  They are using the bottom to hide and then when they see one of the seals at the surface they ambush it with great speed that carries it out of the water.  This behavior has only been witnessed a handful of times outside of S. Africa.

As larger and smaller fish are harested from the seas, thereby reducing the amount of natural prey of predators like sharks, do you think that sharks will have no choice but to attack more human-like objects?

Unfortunately we are killing large predatory sharks at a rate of roughly 73 million per year so they are disappearing faster than the fish and marine mammals that they feed on.  

I know that predators at the top of food chains can be particularly sensitive to ecological disasters if one or two food sources are affected. What is the potential magnitude of the impact on Atlantic Shark populations of this BP Spill? How long do you expect we'll see those effects?

The potential for long term damage to shark populations is huge!  This disaster could affect the entire gulf ecosystem for decades.  The gulf is home to a huge variety of shark species, many of which use the northern Gulf of Mexico to pup and then the young stay in the area for years feeding on the abundant fish.  As sharks are slow to mature, have few young and often do not breed every year this spill could throw off that cycle for years to come. 

There is also the direct affect to sharks that get oil on their gills and then suffocate or the ones that are poisoned through eating small levels of toxic oil residue in numerous fish called bioaccumulation.

I'm sure you're familiar with the Farallones Islands on the West Coast, and the great white haven that the area pretty much is. Is there anywhere on the east coast similarly known for such a reliable concentration of great whites (or any other particular species)?

There are some great shark spots on the east coast.  These waters off Montauk, NY are a great spot to see blue sharks and mako sharks and then the wrecks off of North Carolina have huge populations of sandtiger sharks.  The wrecks off North Carolina are one of the only places in the world to see sharks on an almost guaranteed basis without any baiting activities.

Do you ever get the sense that people are "training/encouraging" great whites to breach in non-African waters, moreso than just observing the behavior?

The only place the breaches really happen is in South Africa.  There are a very small number of operators in that area and they noticed it first as a natural behavior.  In the shows they often tow the decoys so that they can focus on one area that the behavior is likely going to happen but from my understanding outside of filming opportunities they are not out there towing decoys on a daily basis.  Such a small level of towing activity would not really train a shark to attack targets more than seals.

I have been obsessed with sharks for as long as I can remember, so I really appreciate this discussion. For those of us not lucky enough to be in your field, but want to experience sharks first hand, what would you recommend? Are the shark dives offered by commercial dive companies good (for the sharks)? Or is there another alternative that we should consider? Thanks!

Earlier I mentioned the shark diving in North Carolina where no bait is used and that is a great place to see sharks naturally.  Shark feeding dives are controversial.  It is true that we know the bad repercussions of feeding bears in the national parks as they learn that behavior.  Sharks also learn that behavior the difference is we are not living in the ocean and having sharks invade our neighborhoods looking for trash.  There is no doubt that these feeding dives condition a handful of sharks in a given area and their behavior is slightly altered.  

Some recent research has been done in the Bahamas looking at sharks at a feeding site.  It was determined that the sharks are not getting near enough food to sustain themselves and they have been tracked hunting for food.  Some sharks from these locations have even traveled hundreds of miles where one from the Bahamas was actually caught off of Cuba so they are not so conditioned that it is completely changing their behavior.

Again there is pros and cons to this argument.  Personally I feel that if done responsibly shark diving can be a good thing.  I have met literally hundreds of people that have become shark advocates after going on a shark dive.  So I guess you could say the small number of sharks that are conditioned in these locations have become ambassadors for their species.  Also it is important to not there has been no increase in shark attacks at any of these locations or nearby beaches so they are not recognizing people as food but rather a location where they will be fed.

In an ideal world we might not need to do this but with reduced shark populations around the world this can be the best way to see a shark up close and often that is a life changing event in favor of the sharks.

This is my personal opinion however.

You write, "Unfortunately we are killing large predatory sharks at a rate of roughly 73 million per year so they are disappearing faster than the fish and marine mammals that they feed on. " I've read that predatory fish like cod and tuna have been fished out of the sea and that sharks are endangered by shark-fin hunters. Which species of sharks are most endangered, what does that mean to most ordinary people and what can ordinary people do to prevent shark species from going extinct?

Great questions.  First and foremost don't eat shark fin soup and leave any restaurant that serves it and tell them why you are doing so.  Secondly use a sustainable seafood program such as Seafood Watch by Monterey Bay Aquarium when selecting your seafood choices to reduce sharks caught as bycatch (unintended catch).

You can also visit the sites of Discovery's conservation partners Oceana, the OCean Conservancy, and PEW Environmental Trust and support the Shark Conservation Act which will eliminate shark finning in the United States.

Other than oceanography, what other degrees/specializations would you recommend that some pursue if they think they would like an active, firsthand, and directly "shark-based" career? What will we need in the next 5-10 years?

We need more shark scientists.  The best college programs are in marine biology, ecology, or other biology related course work.  Most importantly is get involved early at a public aquarium or as a volunteer for a research program or conservation group as that will help you stand out from the crowd.  Working with sharks is an incredibly rewarding career.  There are some great recommendations in a book called Careers with Animals.

I hear there is a bill in Congress to improve U.S. shark protections. What's that about?

The Shark Conservation Act.  It has passed the House and is up for review in the Senate.  This would ensure that all sharks caught in US waters are brought back to port with their fins intact so that the awful process of finning does not continue in our country.  This is a huge step for shark conservation and our ability as a country to lead the way.  Clearly we need more protection for sharks and shark populations but this is a critical step in the process.

Do you think this comment in today's article is reasonable? "It could even be more dangerous to walk by the office Coca-Cola machine than it is to swim with the great whites."

I unfortunately have not read the article but there is a factoid out there that I have never confirmed that more people are killed every year by vending machines.  This certainly could be true as on average 5-6 people per year in the entire world are killed by sharks.  There are numerous things far more dangerous to people than sharks such as lighting, boating accidents, bee stings, dogs, hitting deer with your car, etc and the list goes on.  We always have to respect sharks as large predators as we do bears and mountain lions but the truth is they are not out to eat humans.

In the wild do sharks usually prefer larger fish as food (such as tuna) or do they sometimes go after smaller species that they can just swallow?

It really depends on the species.  There are well over 400 species of sharks ranging from 6" to 40'.  Oddly the largest shark the whale shark feeds on tiny plankton.  Other sharks like the tiger sharks prefer sea turtles and have teeth adapted for sawing through turtle shells as eating a turtle in one bit is a bit out of the question.  Some small sharks even have flat molar like teeth for crushing small clams and scallops they get on the bottom.

Are there any examples of a shark directly saving a human's life?

Not that I am aware of.  Sharks are far more intelligent than we make them out to be.  In fact in the aquarium setting we have trained them to do some fairly complex behaviors and they learn it quickly.  That being said they do not have the intelligence of marine mammals like dolphins who have been known to save people.

I've seen plenty of sand sharks and the like down along the outer banks of N.C. Do any of them actually either live in the bay or come up the bay any significant distance?

Sharks live in almost all coastal habitats.  All sharks except the bull shark need salt water to live but can tolerate lowered salinities of 15 parts per thousand (normal sea water is 32 parts per thousand).  The Chesapeake and Delaware Bays here in our region have lots of sandbar and sandtiger sharks as these are prime pupping grounds for these species.  The reality is that most people have been far closer than they wish to think to sharks but sharks are not out there attacking people on a regular basis and generally leave us a lone.

All shark scientists and marine biologists probably know that Peter Benchley, author of "Jaws" has since said that he wishes he'd never written that book because of the massive effect it had on people's irrational fears of and subsequent willingness to harm sharks. Do you know if anyone has ever approached Benchley and offered to take him out on the ocean to swim with and observe sharks and film it for broadcast....that could be a great Shark Week show, with a great message.

Peter Benchley became a huge advocate for shark conservation and his wife still is.  Unfortunately Peter passed several years back but did get the chance to swim with sharks.  Peter Benchley wrote an amazing fictional horror story which was what he meant to do.  Just as Steven King wrote a great story about a killer St. Bernard Cujo.  I believe that our fear of the ocean in general our sense of the unknown and not being able to see what is below us is why it struck such a cord with our psyche.

Shark show always have references to shark size. What is the measurement standard? Is it tip of nose to furthest opposite point on the tail?

Tip of nose to far end of tail is known as total length and is the standard used.

For those us wanting to do more, is their a specific charity you can recommend we donate to to help with shark conservation or even a good organization that needs volunteers?

Oceana and the Ocean Conservancy are great organizations very involved in shark conservation.  The PEW Environmental Trust is also very involved as is the National Aquarium Institute with both of our aquariums in DC and Baltimore.  Sharks need your help and I am so excited that you are interested in helping.

"This certainly could be true as on average 5-6 people per year in the entire world are killed by sharks. " I guess this means it is safer to jump into an active volcano than cross the street, since more people are killed crossing streets than are killed in volcanoes. Good to know.

Literally millions of people are in our oceans every day and are not attacked by sharks so I do not think that is the same as a handful of people that might jump in a volcano.  The risk of shark attack is very low.  Less than 100 per year globally.

Thank you all so much for all of your shark questions.  I am sorry I could not get to every one.  It is always great to see so many people every year interested in sharks as it will truly take us all to save these amazing animals. 

In This Chat
Andy Dehart
Andy Dehart is director of biological programs at the National Aquarium in Washington, D.C., and currently Discovery Channel's resident shark expert.
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