Shark Expert and Director, Biological Programs, National Aquarium, Washington, D.C.
Monday, August 3, 2009 1:00 PM
Marine biologist Andy Dehart will be online Monday, Aug. 3, at 1 p.m. ET to discuss sharks and this year's Shark Week on the Discovery Channel, which features six documentaries covering sharks at night, high fatality hot spots around the world, the story that inspired "Jaws," a Navy SEAL's account of being an attack victim, the summer of 50 shark attacks (2001) and the great white.
Read the TV Week article titled "Plumbing the Depths of Intrigue."
Andy Dehart: Hi Andy Dehart here and I look forward to talking sharks with all of you today. I have worked with sharks for roughly 20 years and I always love engaging people in conversation about sharks. So I hope you brought some good questions today.
Chapel Hill, N.C.: When did your passion/fascination for sharks develop? Why?
Andy Dehart: My passion for sharks began when I was only 5 years old. I was snorkeling with my dad in the Florida Keys and we had a 6' Caribbean reef shark swim right by us. The shark was not aggressive at all and I was absolutely amazed by the sharks elegance and serenity and I knew I wanted to work with sharks my entire life.
I consider myself very lucky having the jobs I do. Despite not always being the best student I stuck with my dream. I got involved in the aquarium industry while in high school at the National Aquarium in Baltimore. I took a brief break from there to help build an open the Scott Aquarium at the Henry Doorly Zoo in Omaha Nebraska but returned to Baltimore in 1998. I then moved on to the newly renovated National Aquarium in Washington, DC shortly after the two facilities partnered in 2004.
I joined the Discovery team last year as their shark advisor. I feel I have the two best jobs in the world! Most of all I get to talk about the importance of sharks all over the nation.
Washington, D.C.: How much territory can a shark cover in its life? Do sharks tend to move around or do they typically stay in one place?
Andy Dehart: Shark migration is dependent on the species. Some smaller reef dwelling species will not move very much in their lifetime while other species travel great distances. The longest migration on record is a great white shark named Nicole that was tagged in South Africa then swam directly to Australia and then straight back in under 9 months. This was a roughly 2200 mile migration.
Andy Dehart: So you can see with an animal that travels this far we need to work with other countries to not only ensure we protect them in the US but they do as well or our sharks that migrate south will not return.
McLean, Va.: How fast can sharks swim?
Andy Dehart: Most sharks cruise at a speed of roughly 3 miles per hour but some are capable of incredibly fast bursts. The shortfin mako can swim over 40 miles per hour in short bursts. Another fast species which I will be working with in August is the salmon shark. They have been reported to swim 55 miles per hour.
Washington, D.C.: A lot of people are scared of sharks -- how do you explain to them that sharks are an important part of our oceans?
Andy Dehart: First it is understandable people might have some fear of sharks. They are large predators that have attacked people in the past although very rare (less than 100 per year worldwide). Couple that with the fact that sharks live in the ocean which is a foreign environment to us. Often time our senses are taken away when we are in the fear of the unknown intensifies our fear of sharks.
First and foremost I like to tell people about the risk being so very low. It is far more dangerous to drive to the beach that swimming at the beach. I try to also talk to people and share my peaceful and wonderful encounters with sharks. I have had well over 1000 encounters with large sharks many with the tiger shark (second most dangerous shark) and all have been fantastic not dangerous.
Montgomery Village, Md.: What types of sharks are found off the Maryland coast?
Andy Dehart: Believe it or not many of the sharks featured at the National Aquarium are from the Maryland or Delaware shore. The most common shark is the smooth dogfish a smaller shark species not getting much larger than 4'. Sandtiger shark and sandbar sharks are also quite common. The sandbar sharks actually use Delaware Bay as a nursery and pupping ground. As these sharks are heavily fished it is important we save this important habitat.
Los Angeles, Calif.: What are your thoughts of the movie "Jaws"? Did it create many misconceptions about sharks?
Andy Dehart: We have to remember the novel Jaws by Peter Benchley was only written to be a good horror novel. It was not intended to vilify sharks. Once he realized that it did that he became one of the most vocal shark conservation advocates out there. If you look at Cujo and Jaws they are similar movies about normal animals gone bad, but yet we do not fear St. Bernards. I do think the fact that sharks live in the ocean where we are not comfortable plays are large part in that. They are also not furry and have obvious teeth and blank appearing eyes.
But I do feel public perception has changed immensely since Jaws through programs on Discovery Channel's Shark Week and from people getting up close and personal with large sharks at public aquariums and even getting in the water and diving with sharks. All of these things were not readily available when Jaws first came out.
It has been a slow climb for sharks but I do feel they are being respected for their role in the ecosystem and not just feared. The Shark Conservation Act of 2009 which passed the House and is up for review in the Senate is a good example of that. There is a lot of political and community will to save sharks, but we need more of you.
Lowell, Mass.: I know that some sharks, like the nurse shark, are able to rest on the bottom and keep enough water moving across their gills to breathe. But if a faster-moving open-water shark like a mako were kept still, would it have difficulty getting enough oxygen from the water to breathe?
Andy Dehart: Roughly half of the over 450 species of sharks do need to swim to breathe. They are called ram ventilators. Some of these species can stop for very brief periods but if you stopped a mako shark for even a short time without pumping water over it's gills it could be fatal to this species.
Washington, D.C.: Are sharks the ocean's ultimate predator or can they also fall prey to other creatures of the water?
Andy Dehart: Sharks are one of the apex or top predators in the marine ecosystem. There are roughly 450 species of sharks in the world with over half of them being less than 3' long. Many of these small sharks are actually eaten by other sharks and other animals. There is even a confirmed report of a giant Pacific octopus eating a dogfish (a small type of shark). Some of the larger species of sharks like great white, tiger and bull have very few predators other than man although if threatened bottlenose dolphins and orcas have been known to kill sharks.
The importance of this is that sharks are keeping the oceans ecosystems in balance and if we remove the sharks we will throw off the entire system.
Elba, N.Y.: Do sharks raise their young?
Andy Dehart: There is no maternal care for shark pups whatsoever. Shark pups are born ready to hunt and survive although many do not live to adulthood due to fishing pressures and are eaten by other creatures.
Silver Spring, Md.: Hi Andy! Thanks for taking questions. I love shark week; in fact, it's probably the only week out of the year where I feel compelled to watch TV every night. I am a recreational diver, but have never seen a shark. I'm heading down to the Bahamas in the fall and am considering a shark dive. The problem is that every bone in my body tells me it's wrong to be baiting those fish so that geeks like me can be near them. Can you offer any validation to me? You know what, just tell me it's wrong and I'll be on my way.
Andy Dehart: Shark diving can be controversial. In my personal opinion though it is good for the change it makes on people. I am very good friends with Stuart Cove of Stuart Cove Dive Bahamas one of the most popular shark diving places in the world. He has partnered with Simon Frazier University to look at the effect of these feedings. What they have found is that the sharks are getting the equivalent of a grape a day in terms of food and are utilizing the reefs in their normal fashion. In fact the reefs where they do the feedings seem healthier.
Obviously these animals are getting conditioned to be around people but they have shown that if the feeding stops the sharks are capable and able to go hunt on their own and are not attacking people.
I consider these animals as ambassadors for their species. Yes their behavior is ever so slightly altered but they are making a huge impact on people. I have been on so many dives with people all over the world that have been literally petrified to be in the water with sharks but after the dive they have been ready for another encounter.
That being said there are good and bad ways to do diving with sharks. I prefer the operators that use a set method and that all operators to that site agree in the same method be it pole feeding or a "chum-cycle" a frozen block of chum suspended in mid water.
The argument is that you would not do that in a national park with bears but unfortunately in the ocean we have a very limited amount of time we can spend there and shark populations are disappearing rapidly so this is a low impact way to ensure people can see these amazing animals.
Keep in mind that is my own personal opinion.
Clemson, S.C.: Do sharks respond to vibrations in the water like they said in Jaws?
Andy Dehart: Sharks are very sensitive to low frequency vibrations like those made from a wounded fish.
Grand Rapids, Minn.: How far have Bull Sharks traveled up the Mississippi River? Was there ever any attacks?
Andy Dehart: I have heard of a report of a bull shark in St. Louis. I do not know how far north there has been an attack. They have also been observed over 2000 miles up the Amazon River.
Richmond, Va.: Is there one dive that you have been on that sticks out from the rest?
Andy Dehart: Honestly every encounter I have had with sharks has been special. I have had a few that really stick out though...
My first dive with a tiger shark I was 16 years old and we had to literally push this 15' tiger shark with an eye the size of a plate through the water. She had been on fishing gear all night and we needed to revive her after tagging her and measuring her and I drew the short straw. It was certainly one of the reasons I focused on tiger sharks after that as it was such an amazing day.
Recently one of my best dives was with the sixgill sharks in the dark and cold Puget Sound in Washington during the filming of Shark After Dark.
My wife (also a marine biologist) and I got engaged underwater, go figure, so that has to be up there in my favorite dives as well.
Washington, D.C.: My five-year-old son loves sharks...but would this documentary be appropriate for someone his age or would it result in years of fearing the water...even the bath tub?
Andy Dehart: My six year old nephew loved it and I think it is quite kid friendly. There is no attacking but some sharks eating bait. But certainly you know your children's sensitivities the best. Also feel free to bring him down to the National Aquarium in Washington, DC one day. I would be happy to talk sharks.
Washington, D.C.: Shark attacks often get sensational treatment from the media, which portrays sharks as "serial killers" of the sea. What is the best way to protect sharks from becoming a victim of their own infamy?
Andy Dehart: I think it is entirely possible to respect sharks and protect sharks for the role they play in the ocean without them being adored.
The true problem here is not that we are killing sharks because we fear them but rather their fins are extremely valuable. Just as elephants, rhinos, tigers, etc are all still being hunted despite being endangered the sharks have something that humans will pay big money for and until consumption stops shark fishing will go on. Many of the worlds open oceans are not protected and are open for full scale fishing on sharks.
We have to work with our government to save sharks for their role in the ecosystem and because they are not well suited for a commercial fishery. The Discovery Channel, the National Aquarium, the Ocean Conservancy and many other environmental groups have all endorsed the Shark Conservation Act of 2009 which will hopefully ensure the practice of finning stops in the US and closes a loop hole allowing trade of fins at sea.
If the US is not protecting sharks in this fashion we can not work with other countries to help them do the same.
Washington, D.C.: Are all sharks carnivores?
Andy Dehart: Yes. Even the whale and basking sharks are eating zooplankton a type of animal.
D.C.: How did you develop your interest in sharks and what type of schooling/experiences prepared you for this kind of work? Have you ever worked with survivors of shark attacks?
Andy Dehart: I touched on what got me into sharks earlier in the blog. I started my college career studying marine science at Eckerd College but was offered a job to help build an open an aquarium in Omaha Nebraska at the Henry Doorly Zoo between Jr. and Sr. year so I transferred to general biology. Unfortunately I was not the strongest student in the world but what I lacked in grades I made up for in determination. I took on every opportunity to volunteer and do internships that I could and it obviously worked as I have the two best jobs there is. Obviously you need to study hard but for me determination and passion to follow my dream accounted for just as much.
I have worked with a number of shark attack survivors and am always amazed by their stories. I have found it amazing that most of the people I have met have not had any ill feelings for sharks at all. The risk of attack is so very low but for these people the statistics do not mean much it is much more personal. Part of why I have so much faith that we can save sharks is by the passion many of these shark attack survivors have for saving the animals that hurt them.
Alexandria, Va.: I am heading down to the Outer Banks of North Carolina for two weeks at the beach...is there anything I should be concerned about in the water?
Andy Dehart: Not at all. Enjoy the beach and be careful driving. That is the dangerous part.
Wilmington, Del.: Earlier in the chat, you wrote that the Tiger shark is the second most dangerous shark. What is the first? A few years ago Shark Week named the Bull shark as number 1, but I would have thought the Great White is more dangerous.
Andy Dehart: Great whites have more recorded attacks but the bull sharks have a more aggressive temperament. So depends on how you look at it. Tiger is number two in terms of numbers but all of my experiences with them have been like hanging out with great danes.
Phoenix, Ariz.: Do sharks have live young or do they lay eggs like other fish?
Andy Dehart: Sharks have young in three ways depending on the species.
1) live young very similar to mammals
2) lay eggs that hatch in the ocean
3) lay eggs that develop in the mother then hatch and are born live.
This is the laymans version of course.
Los Angeles, Calif.: Can you be more specific concerning Discovery's new initiative to ban shark finning?
Andy Dehart: They have publicly supported the Shark Conservation Act of 2009 proposed by Sen. John Kerry that will outlaw shark finning in the US and close a loop hole allowing trade of fins at sea.
Washington, D.C. : Can sharks really smell blood?
Andy Dehart: Absolutely they have incredibly strong senses of smell. One report claimed a lemon shark could smell one drop of blood in an olympic size swimming pool.
Durham, N.C.: What has been your scariest shark encounter?
Andy Dehart: It has been watching a fishing vessel remove the fins of sharks on video.
In person I honestly have not had any truly scary times when I felt my safety or life was in danger.
Mount Holly, N.J.: How long do sharks live?
Andy Dehart: Some sharks likely live 40 years. We believe some cold water species may even live 70 years.
Chincoteague, Va.: Is the world population of sharks growing or shrinking?
Andy Dehart: We are killing sharks at a rate of 250,000 per day so they are shrinking rapidly. Some species like the scalloped and great hammerhead have had their populations reduced by 89% in just 20 years. Sharks are slow to mature, have few young and do not always breed every year. Without protection some species may disappear in our lifetime. You can help by not eating shark fin soup or eating at restaurants that serve it and by making wise seafood choices as many sharks are inadvertently caught as bycatch.
Arlington, Va.: Thanks for sharing your expertise with us! I was wondering if you could touch the subject of sharks seemingly not susceptible to cancer. How much research is being done currently? Also, do you think it is likely that shark preservation and awareness would increase if the public had faith that a cure for some types of cancer may be found in these beautiful creatures?
Andy Dehart: Sharks do in fact get cancer although it is rare. Researchers are always looking at ways that sharks might help in terms of human medicine. The reality is however shark cartilage pills will not help prevent cancer. It would be like taking pills of ground up hair to prevent male baldness.
Philadelphia, Pa.: Is it true that, even though sharks will bite a human, we really aren't on their menu and they usually spit us out?
Andy Dehart: Humans are not on the diet of any shark species. Often times when we are attacked because we are mistaken for their normal prey the shark does swim away never to come back.
Andy Dehart: Everyone, thank you for your fantastic questions. I am sorry I was not able to answer them all. I hope you will all help me pass the word the sharks need our help to survive. In conclusion what you can do...
1) Don't eat shark fin soup or eat at restaurants that serve it.
2) Make wise sustainable seafood choices. You can find out more at Monterey Aquariums web site.
3) Don't buy white shark teeth from gift shops or buy shark cartilage pills.
4) If you fish for sharks start tagging not killing.
5) Support the Shark Conservation Act of 2009
Thank you so much and Best Fishes to you all.
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