Animal Week: Sharks and Marine Life

Alan Henningsen
Marine Biologist/Shark Researcher, National Aquarium
Thursday, April 13, 2006; 1:00 PM

Marine biologist and nationally recognized shark expert Alan Henningsen of the National Aquarium in Baltimore, Md., was online Thursday, April 13, at 1 p.m. ET to answer questions about these widely-feared ocean predators and all other marine life, from whales to dolphins to jellyfish.

The transcript follows.

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Minneapolis, Minn.: My fiance and I have a Malaysian box turtle who spends most days swimming. Sometimes he seems to recognize us and swim excitedly at the glass and other times he'll pop his head in. Do reptiles have any kind of memory? Is it more traumatic for him if we interfere with him other than cleaning his tank, or will he learn to like the occasional holding?

Alan Henningsen: Hello. Reptiles such as your box turtle do have memory and the ability to learn. I suggest that if you do have concern over the turtle that you consult with your veterinarian.


Alexandria, Va.: Dolphins are known to be intelligent animals. How are they trained? Do they communicate their feelings to humans in the ways that dogs do (expressions, body language, etc.)? When they communicate among themselves, is it through sound only?

Alan Henningsen: Intelligence is a difficult topic because we have a hard enough time measuring intelligence in people!

We use positive reinforcement to train any animal at the National Aquarium in Baltimore, including our dolphins. That basically means we reward good behavior and ignore unwanted behaviors. The animals are never punished if the do not do what we ask.

Dolphins do have the ability to communicate; they use whistles and clicks and they also use body posturing and movements, such as tail slaps, to communicate.


Washington, D.C.: Are crustaceans sentient animals?

Alan Henningsen: Intelligence is extremely difficult for us to determine.

You may wish to consult with an ethologist (a person who studies animal behavior) for a more thorough answer.


Chapel Hill, N.C.: I've often been befuddled by the press coverage that a single shark gets, even if it's on the other side of the world. Seems more people get attacked by clowns than sharks, but judging by the sensational coverage attached to shark-attacks you'd think this was a huge problem. Why do you think that is? Is it "Jaws" syndrome? Something else? Why wouldn't people equate swimming in the ocean with walking in the jungle, where you may be likely to encounter wildlife such as bears, lions, on land, and an occasional shark in the water. When people swim, they are swimming in a jungle. Why is it so hard for us to accept there are fish in the ocean who may be hungry?

Alan Henningsen: Thank you! You are correct, the ocean is indeed sharks' habitat. Unfortunately shark attacks do occur, and as you note they are extremely rare. According to the International Shark Attack Files, reported unprovoked shark attacks have actually decreased over the past few years. When these attacks occur, however, they do create sensational news stories. It is important to keep shark attack stories in perspective. You are actually more likely to be killed by wild pigs or lightening strikes than by a shark attack. For more information, please visit the International Shark Attack File's web site.


Pittsburgh, Pa.: Hi Alan,

I'm not sure how many people understand how important sharks are to the delicate balance of the ocean habitat and the sea's food chain. Perhaps, most important of all to those issues, are great white sharks. What is the latest data on their numbers and are they close to making the endangered list? Thanks very much.

Alan Henningsen: You are correct, white sharks's role as apex (top) predators is important in many marine ecosystems. Although no specific studies have document the effects of their dwindling numbers in any location, published models of other apex predators, including sharks, have depicted various scenarios that result from the loss of the predators. In these cases the food web becomes extremely unbalanced.

White sharks were listed by Convention in Trade in Endangered Species (CITES) under Appendix II. This does not prohibit trade of this species (or its parts) but it does mandate monitoring of the trade. White sharks are protected by several countries worldwide. In the US they are considered a protected species.


Washington, D.C.: I have an irrational fear of sharks, which subjects me to friendly ridicule from time to time. While I love going to the beach, going into the ocean is not an option. Do you have any suggestions on regions of the world that have a limited shark population (all cold climates are already out of consideration).

Alan Henningsen: Sorry for the "bad" news, but sharks are found around the world: in the open ocean, coastal regions, and in cold, warm and temperate water. They are important to the balance of our aquatic ecosystems and negative encounters are extremely rare.

Many negative encounters occur in murky waters where the shark has a harder time determining what is prey. You may more comfortable swimming in waters that are very clear, avoid wearing jewelry, and avoid areas with schooling fish. To alleviate your concerns more, you may wish to consult the International Shark Attack Files.


Erie, Pa.: What is your explanation for whales beaching themselves? Do you believe that that could be a result of military sonar and/or seismic testing?

Alan Henningsen: Many theories exist for why whales strand. I'm not a marine mammal specialist, but can suggest that you check out the Aquarium's newest publication, Marine Mammals Ashore: A Field Guide to Stranded Marine Mammals.


Detroit, Mich.: Is there any particular sealife that is becoming endangered by global warming?

Alan Henningsen: The whole planet will be affected by global warming, so it will eventually impact all the Earth's ecosystems. The most fragile ecosystems, like rain forests, coral reefs and polar regions, will most likely be less resilient.


Bethesda, Md.: When I went to the National Aquarium around 1997, I liked the sharks and so on, but I think the jellyfish exhibit was my favorite. Is that still there?

Also, what is the major threat to ocean life? (I know, man-- but fishing, pollution, what? I read about whales up in Canada having enough toxins in their body fat to be considered biohazardous waste)

Alan Henningsen: The jellies exhibit is no longer here, but we have an incredible new, permanent exhibit called Animal Planet Australia: Wild Extremes. It has animals not seen anywhere else outside of Australia and is the only one of its kind in North America. Come check it out!

Everything you listed is a threat to marine life. Also, habitat degradation, directed fishing (overfishing of certain populations), and bycatch (animals accidentally caught while fishing for another species) pose problems to marine life.

Beluga whales and Greenland sharks in some regions do have enough toxins in their body to be considered dangerous. This is because of a process called bioaccumulation - the toxins get carried up the food chain and their effects become more pronounced because the toxins are stored in fat-containing tissues, such as livers.


Dallas, Tex.: I heard many years ago that sharks are immune to cancer. Is this true? If so, have scientist discovered why?

Alan Henningsen: This is a common myth. The number of tumors reported in sharks, skates and rays is less than those found in other vertebrates. They do, however, develop several types of tumors.

Please keep in mind that this finding may be due to a lack of reporting, as they may not have been studied as extensively as other animal groups.

Many people take shark cartilage supplements believing that it will help protect them from cancer. No scientific evidence supports this.

Unfortunately millions of sharks continue to be killed for their cartilage and other body parts.


Charlottesville, Va.: If a shark and a grizzly bear fought, who do you think would win, and why?

Alan Henningsen: The chance of a shark and grizzly bear encountering one another is remote.

The basis of your question, though, is common and too many factors exist for us to try to answer such questions. Sorry!


Falls Church, Va.: My fiance enjoys scuba diving and snorkeling. I tried both for the first time on our cruise to Caribbean and enjoyed my experience. The only issue I had was I was a little worried in encountering a shark. How often do divers encounter sharks and what is the best way to protect myself? Thanks!

Alan Henningsen: Sharks live around the world and you may observe some while diving. Feel honored! They are magnificent creatures and they will often shy away from us.

The frequency of encounters depends upon the location, time of year, and species of shark.

To protect yourself from sharks, fire corals, jellies, sea urchins, and anything else that could be potentially dangerous, simply follow safe diving guidelines and be aware of your surroundings.


Crozet, Va.: If you were a shark, what kind of shark would you be?

Alan Henningsen: I wouldn't be a shark - I'd by a type of ray called a sawfish. Sawfish are endangered rays with long snouts (called rostrums) covered with teeth, but these teeth are not like the teeth in their mouths. They use their rostrums for feeding and defense.

I could go on and on about sawfish, but there are more questions waiting!


Swimming with dolphins: What is your take on those programs that you let you swim or interact with dolphins in the guise of an educational effort? Are they cruel? Also, is it true that dolphins can sometimes go crazy when kept in captivity, and will start swimming neurotically, banging their heads into walls?

Alan Henningsen: Interactive programs in the wild or in protected environments, like aquariums, should be teaching opportunities. It is important for people to understand more about these animals' natural history and behavior.

In the U.S. dolphins are protected species and are regulated by the federal government under the Marine Mammal Protection Act.

Any facility in the U.S. that houses marine mammals (dolphins, whales, seals or sea lions, for instance) must meet federal regulations to ensure the well-being of these animals.

Animals participating in these programs in the US are specially trained to interact with people. Their health and behaviors are continually monitored by veterinary and animal care staff.


Washington, D.C.: Do know about how far north on the East coast is there a significant shark population? I've been operating generally under the assumption that, say, the waters of the Maine coast are far too cold for my multi-toothed friends. Am I wrong?

Alan Henningsen: Sharks are found worldwide, in the open ocean and along coastal regions. Along the coast of Maine, seasonally you can expect to find, for example, spiny dogfish, smooth dogfish and sandtiger sharks. Further off-shore, you will find makos, chain dogfish and blue sharks.


Washington, D.C.: I too have a largely irrational fear of sharks, though I love learning about them all the same. Is it true that even very large sharks can be found swimming in waist-high water? I ask, as I've seen very large birds swooping down into the water just beyond the surf, so there are clearly substantial fishes in there. Might a shark venture in that far for food?

Alan Henningsen: Sharks of all sizes are found along our coasts. If you see birds diving, that generally indicates that they are feeding, and it would not be unreasonable for a predator, like a shark, dolphin, bluefish, or barracuda to be there, too.


Munich, Germany: I read a report recently that the population of larger ocean fish has been reduced to 10% of levels from 50 years ago.

Is there a chance that the oceans will someday be overfished into a saltwater desert?

Alan Henningsen: It is a serious concern for many species of marine organisms, including fish.

It is a big concern for sharks and their relatives because of the role they play in the marine ecosystem and because of their life history characteristics. Unlike most bony fishes, sharks and their relatives tend to grow slowly, live long lives, bear few young, and mature later in life. This means that if their populations are not properly managed, they'll have a hard time rebounding and if they can rebound, it will take decades. Sharks really do need our protection. They should not be feared.


New York, N.Y.: How has global warming affected our planet's sea life and sea mammals? Does it confuse whales that are migratory?

Alan Henningsen: We do not know the full effects of global warming today, as some of the impacts may be delayed. We are concerned that all environments will be impacted.

Many people are taking steps to help protect our environment. Some easy, but effective, steps you can take to help are: take shorter showers, use low-flow shower heads, turn off lights and other electrical devices that aren't being used, buy a hybrid or other fuel efficient vehicle, combine errands and, it probably goes without saying at this point, but remember to recycle.


Alan Henningsen: I'd like to thank everyone who submitted questions today.

Sharks, skates and rays are my favorite animals and should be respected not feared.

We heard from quite a few folks who admitted they are afraid of sharks, and I'd like to reiterate that the chances of being attacked by a shark are very, very slim. If you'd like to learn more, I encourage you to visit the International Shark Attack Files' Web site, and of course, the National Aquarium in Baltimore's Web site,

Several species of sharks, rays and skates are threatened, endangered, and even critically endangered. They have much more to fear from us than we do from them.

Thank you in advance for your efforts to save the sharks, skates, and rays.

Alan Henningsen


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