Dirty Jobs

This episode is completely dedicated to sharks. They start the show in the Indian Ocean off the coast of South Africa looking for great white sharks. Mike is with the guys from Shark Adventures on board the Predator 2, a boat with a large shark cage mounted to the back. Brian is the captain of the ship. He explains to Mike that they have a cutout image of a seal (named Gladys) to lure the sharks. Sharks at the bottom will see this cutout, think it's a real seal and come up to the surface. Brian uses two or three decoy seals like this one every day.

They are about ten kilometers out from the town of Gansbaai in an area called Shark Alley. Nearby is a small island (Dyer Island) inhabited with 23 types of sea birds - and their poo. Mike is intrigued by this and wants to visit. (Sadly, it is a nature reserve and visitors are not allowed.) There is another small island (Geyser Rock) which has nearly 60,000 Cape Fur seals living there. Sharks congregate here because they love the smell of seal poo coming from Geyser Rock. As Brian explains it, during low tide the seals "make all their messes" and at high tide the messes and smells float into the water which attracts the sharks.

After throwing Gladys the seal decoy into the water, they lower the shark cage. It slides into the water from a wooden plank. There are floats to keep the cage from sinking to the bottom. Mike has trouble undoing the knots on the ropes holding the cage. Brian gives him a hand and they push the cage in. They tie the cage up right next to the boat.

They also need to get some smelly oily chum in the water to attract the sharks. This consists of a sock filled with raw tuna. Mike gets to fill the sock. 80% of a great white's diet is fish. Only 20% of their diet is seals which is why they use tuna as chum rather than seals. (Also, they can't use mammals as chum.) Mike lies down at the edge of the wooden plank to ties the chum bag to the side of the boat. Brian scares Mike by saying a shark could come up and bite off his head. You can see the oil from the tuna shine on the surface of the water. This is what will attract the sharks.

Brian also has a bunch of tuna heads. These are good at attracting sharks because the gills contain blood. Mike is given the task of cutting off fatty pieces of fish for bait. His hands are getting slippery and he is told to wash his hands off in the water. He doesn't like that idea.

The seals are constantly coming and going in this area and the sharks are always patrolling around the island. The seals know they are safe inside the kelp beds. However, once they stray out of the kelp beds, that's when the sharks can get a meal. Seals have to go out into the open water to go hunting and the sharks in turn hunt the seals.

Kelp is a type of seaweed. Sharks don't like it and will avoid the kelp beds because they don't like anything touching their bodies. Kelp has long stems rooting it to the ocean floor making it hard for the sharks to swim around it comfortably. Brian suggests that if you're swimming and see a shark, head immediately for a kelp bed for safety.

Next they need to throw their chum into the water. Brian says they're not going to feed the sharks. They are going to throw the bait into the water and pull it away when a shark comes up for it. The bait is just there to get the shark's attention. The chum is tied to a rope and thrown into the water.

Nowhere in the world will you find a great white shark in captivity. Sharks are easily stressed and just don't survive in an aquarium. They can only be found in the wild which is why people travel the globe to see these sharks up close. They can only be seen closeup on boat tours in Australia, Mexico, California and South Africa. South Africa has the highest success rates when it comes to seeing the great white sharks.

Mike is ready to see sharks. He throws a tuna head into the water. Brian explains that they're going to wait for a shark to come up to Gladys and then pull the decoy away. Suddenly a great white appears. They're a bit slow at pulling Gladys in, but the crew gets some great close up shots.

Brian explains that sharks don't go after humans to eat them. They usually see a surfer or a diver at the surface and come up to investigate. Granted, the sharks "investigate" with their teeth so it seems like they want to eat the person, but normally they will just spit the person out when they figure out it's not a seal.

Mike throws out another bait line. Almost immediately he is told to pull it back in. A shark has the line in his mouth. Mike just barely gets the bait pulled out in time. He seems a bit stunned by the experience and drops the bait back in as the shark comes back. He's reminded that they're not feeding the sharks and to pull the bait out. He's dangling the bait on the side and the shark keeps trying to grab it. Mike repeatedly throws the bait out and Brian says they're going to get the shark as peeved as possible then put Mike into the shark tank.

Mike notes that the shark cage on this boat is bigger than others he's seen. Brian says this is because people feel as if there's safety in numbers. When one or two people are in the cage, they get nervous. However when there's three or four people in the cage, they feel a bit safer. Today Mike is going to be in the cage with just a cameraman.

Brian feels that today is a good day to go in the cage. The water is calm and clean which is a good combination. He says that the sharks don't come and attack like the Jaws movies. They will be more nervous of you and will only come to investigate the bait. Brian is going to pull the bait close to the cage and the shark shouldn't even know that the humans are in there watching. They actually will move away when they feel a person's nervousness. They can sense the fear. When the person in the cage calms down, the shark will move in closer.

Mike suits up and is ready to climb into the cage. He's noticed that wind has changed and they can smell dead seals and poo in the air coming off the island. Before Mike goes in, Brian tells him the good news and bad news. The good news is that the government allows them to lose three tourists every month. The bad news is it's the fourth day of the month and they've already lost three tourists so Mike has to be very careful so Brian doesn't lose his license. Mike isn't sure what to think of the captain's humor.

They rub fish over Mike's wet suit so he smells like bait. He doesn't like that at all. Adam, one of the members of the ship's crew, helps Mike into a harness and a mask. The mask will not only provide air, but allow them to communicate. When he's in the water, the people on the boat will be able to listen to him scream and he can hear them announce when a shark coming close.

Mike goes down into the cage and the scary music starts. Bait is thrown all around him. Huge sharks come up to the bait. Mike gets a close up view of it all. One even comes up to the cage and starts biting at one of the floats directly in front of him. He quips that he's going to need another wetsuit.

This part of his adventure is over and Mike is brought back onto the boat. He gets out of his wetsuit and discusses what he saw with Brian. Brian asks if he has a new respect for the shark and Mike responds that he never disrespected them in the first place, but he never realized that they were that big. Brian then asks if he thought the sharks wanted to eat him. Mike claims he can't comment on that, but one seemed to be giving him the eye. Brian attributes that to Mike being a good looking guy and attracting the female sharks.

Next Mike shows us the carcasses of sharks. First he holds up a dusky shark. They're called that because of their dusky color. They are also known as gray ridgebacks because of the small ridges on their backs. They hunt in packs like wolves. When they grow to full size they can be a threat to humans.

Mike then shows us a milk shark. They are called this due to a long held belief in some cultures that eating the flesh of a milk shark can help increase milk production in mothers who are nursing. There is nothing to support this belief.

The next shark he holds up is a hammerhead. People are scared of it, but its mouth is so small that it's not much of a threat to people. Mike claims to not see why the shark is called a hammerhead...

He is showing us these specimens from the Natal Sharks Board in Durban, Kwazulu-Natal, South Africa. Their mission is to preserve shark populations. Here, marine biologists conduct autopsies on sharks found dead in the nets that protect swimmers on local beaches.

Mike arrives to assist in the autopsy of a tiger shark. This shark appears to be eight or nine feet long. Its name comes from the tiger-like stripes on its back. We meet Geremy who explains that these sharks are one species that swimmers need to worry about the most. Great whites, tigers and bull sharks historically are the most dangerous. They are responsible for most human shark attacks on coastal waters. Research data from the autopsies is collected and analyzed in order to study the health and behavior of the different species.

Geremy explains the differences of the teeth. The teeth on this tiger shark are in the exactly same shape. However, in other species like great whites, the teeth in the lower jaw are sharply pointed and the teeth in the upper jaw are much wider. Lower jaw teeth provide anchoring and upper jaw teeth provide the cutting of prey.

Mike notes that the teeth are loose. Geremy explains that they're not embedded in sockets like ours. They are attached to a layer of connective tissue at the back of the jaw. He compares it to a conveyor belt. The teeth move from the back of the jaw to the front and as they get to the front, they fall off. Sharks can go through thousands of teeth in a lifetime and by shedding teeth, they nearly always have fully functional intact teeth.

Mike is given a knife and told to cut up the length of the shark. The skin is very tough. They open it up and we can see inside the shark. Geremy explains that sharks do not have subcutaneous fat. We (and other mammals) have a layer of fat located between our muscles and the skin to keep us warm. Sharks are cold blooded. Their body temperature fluctuates with the temperature of the water.

If you're not storing your body fat under the skin, it gets stored in the liver. Sharks have a huge liver. The greenish spot Geremy points out on the liver is the gall bladder which secretes bile and helps with digestion. He also points out the mesenteries which are a mass of sheet-like membranes which connect to the stomach. They hold the small intestines together.

They pull out the liver. It is 25% of the shark's weight. The fat lipids are stored here as an energy reserve. They plop the liver into a bucket and weigh it using a hoist with a scale. They will hook it over the scale where the right and left lobes of the liver are attached. It's so heavy that Mike has a hard time getting it over to the scale. It weighs 17.6 kilograms (about 40 pounds). This is normal for a shark this size.

Geremy says that once the liver is out, there's not much left to the shark. Next they look at the stomach. Sharks don't chew their food. Whatever they bite off is swallowed whole. Muscular contractions of the stomach plus digestive juices help break down the food. The lining of a shark's stomach has cells that secrete hydrochloric acid which helps break down hard objects like bones.

It doesn't appear that there's anything inside this shark's stomach, but they will open it up to check. Mike asks if they ever have found human remains. Sometimes they do. When that happens they have to call the police and have photos taken and fill out affadavits regarding their findings. Geremy doesn't like that part of the job.

The stomach is removed and put in a bucket. They need to turn it inside out to see what's inside. Unfortunately they find nothing but a parasitic worm. Normally worms like this are found in the intestines rather than the stomach.

Tiger sharks are notorious for eating anything they find - even if it has no nutritious value. Geremy says he has found aluminum cans and plastic bags in their stomachs. He's even found some racing pigeons. He thinks they were probably caught in a storm and blown offshore. He found their legbands and contacted the racing pigeon club to notify them of their loss.

Next they look at the gonads (sex organs). Geremy points out the ovaries. This shark appears to be about five years old and is not sexually mature. It varies by species, but some sharks can take 20-30 years to become sexually mature.

These are not nurturing animals. There is no parenting after the young are born. The pregnancy can last for a year and the young (of a tiger shark) grow to be about half a meter in size inside the womb. Once they are born they have to care for themselves. Mike says that he heard that sometimes the young eat each other in the womb. Geremy says that sand tigers do this most often. The mother will produce about ten offspring and the largest embryo will eat its siblings.

They look at the heart next. Mike has to cut through the cartilage that forms the pectoral girdle. It has a two chambered heart that produces a weak blood pressure. In order to circulate blood though its body, this species of shark has to keep moving.

Next they move to the head. The eyelid is underneath the eye and comes up from the bottom. It covers the eye when the shark is feeding. When animals are attacked, they will fight back and the shark's eyes can be damaged since they're so close to the mouth.

Geremy shows Mike the tongue. The tongue is short and attached. They can't stick it out like humans. It's not muscular or maneuverable at all. We use ours for taste and to manipulate food around the mouth. Sharks don't chew their food so their tongues are only used to help swallow.

Mike is given the task of cutting out the jaw. He asks Geremy to show him. The jaws actually aren't made up of bone. It is all cartilage. By cutting out the jaw, Mike hits the eye socket. He pulls out the eye and shows us the lens. Finally he gets the entire jaw out and his day as a shark autopsy technician is done.

Next is part two of this two hour episode. Mike is at False Bay in Western Cape, South Africa. This bay is full of sharks. He is meeting with people from the South Africa Shark Research Center. They are studing the movements and habits of the great white shark to help protect the humans in this recreational area. The great white is a protected species in South Africa.

Mike is on a boat called the Top Predator. They are headed to Seal Island with Alison and Ryan who are working on PhDs on shark behavior. They want to bring the sharks close to the boat so they can tag them and monitor them in False Bay. They have transmitters which are placed at the base of the dorsal fin. The transmitters will send out a signal unique to each tag. When it comes within range of one of their monitors in the bay, it will tell them which shark is in the area and for how long.

We meet Mike who is the research coordinator at the center. He is taking them to Seal Island which is about eight miles from Simon's Town, South Africa. Seal Island has about 70,000 seals to attract the sharks. In the distance they can just barely see a shark eating a seal.

Before they start tagging, they have to set up the targeting device and finish preparing the bait. They are making a chum line out of slightly rotten shark meat. Sharks are capable of sensing blood from two miles away. Lines of bait are thrown out and sharks come up to the boat. Alison plunges the spear-like device into the shark. Once the shark is tagged, the still have to gather information. They had to ID it, get some DNA and sex it. Mike learns that males have two penises called claspers. Plus, no one has ever seen a great white mate.

They have to tag the sharks twice. The second tag will have a different frequency and is tracked by satellite. They can pick up twice the amount of data from the same shark. They track the shark they just tagged with a directional hydrophone which picks up the radio frequencies emitted by the transmitter.

They wait for the shark. Ryan will tag the shark while Alison jots down any identifying marks. Mike notes that the sharks don't always just come in and grab the bait. They're very curious and cautious. Ryan says that as scientists they're not supposed to give the animals human characteristics, but after all the sharks he's seen, he's noticed that they do have different personalities.

After watching other sharks approach the boat, their initial shark comes back. Ryan is ready with a genetic tip that will be punctured into the shark's skin deep enough to retrieve a sample to be used for DNA testing. The shark's skin is so thick, that it is not painful. The DNA will help researchers analyze genetic patterns and individual variations between sharks.

Next Mike travels to Bimini in the Bahamas where he meets Dr. Gruber and Mike Herman. In the cooler Mike is carrying, there is a black tipped shark that a fisherman has donated for research. Local fishermen often donate dead sharks to the Bimini Biological Field Station where they study sharks in their natural habitat.

A small company, Shark Defense, is working out of this outpost trying to develop a shark repellent to be used to protect humans from dangerous sharks. It could also help save thousands of sharks from accidentally getting trapped in fishing nets. Sharks don't like the smell of other dead sharks in the water which is what this repellent is based upon. They're trying to extract this aroma from a shark carcass and bottle it.

Mike opens the cooler and pulls out the rotting shark corpse. The shark is actually in a series of bags inside the cooler, but the stench is still very strong. The flies show up instantly and Dr. Gruber leaves. They want some of the white muscle tissue from underneath the skin. Mike grabs a knife and makes an incision on the bottom. Mike then removes a piece of muscle. The skin is very tough and hard to cut. Once he gets a piece, he stuffs it into the paper specimen holder. He breaks the first one, cuts a smaller piece and tries again. Once they fill the tubes with the rancid shark meat, they are done with this stinky part of the job.

They take the meat to Eric who is a chemist fascinated with trying to find a shark repellent. He first got the idea for it when he learned that fishermen would drag a dead shark at the back of their ships to repel live sharks. He wants to find what it is in decaying sharks that signals other sharks to stay away. He's going to extract the chemicals out of the shark tissue that Mike just cut up.

They put the meat into the center of Eric's glass contraption. Hot solvent will come up a tube, be condensed by running cold water and drip up to six hours. It will concentrate what they want out of the meat. What they don't want will be removed as vapor. What they end up with is a shark repellent that they can bottle.

Mike drops the whole cup into the glass. He tries to keep the flies out. Eric doesn't really like that some flies got inside because it creates an impurity. The specimen holder is made of paper to protect the side of the glass because it will be really hard to clean if they put the meat in all by itself. A full grown shark can make 55 gallons of repellent. They use only half a liter to test on the bigger sharks. Hundreds of liters can be made from just one shark.

They test the repellent by shooting canisters into the water with an air cannon. The gun Mike is shown was designed by Marine Search and Rescue Systems. It can shoot the canister two hundred feet away. This will simulate what a lifeguard would do if there is a shark sighting in the water. Lifeguards are not allowed to go out in the water when there's a shark attack for safety reasons. A boat rescue will occur, but this gun will shoot the repellent further than a human can throw and potentially save lives.

They load the canister and make it a live weapon. A trigger is inserted first. They use a plunger to push everything down which reminds Mike of how muskets were loaded. Then they pressurize the gun using compressed air. It can go up to 200psi safely, but they keep it at 150psi. Mike is given the gun and allowed to shoot it near the boat where the cameramen are located out in the water. Mike wants revenge on the camera crew and he gets really close to hitting them.

They now have to actually test the repellent on live sharks. They are going to a reef about three miles off the coast of Bimini. A diver is sent to lower the anchor so the reef below them isn't damaged. They're having trouble anchoring the boat on this day because the current is pulling them one way and the wind is pushing them another way. There are some dangerous swells. They are going to lure the sharks in with bait, then throw the repellent into the mass of sharks to make them go away.

Chum is thrown into the water and sharks show up immediately. Cameraman Doug is right in the middle of the action. The sharks here are reef sharks and black noses. The cameras are putting off a little electrical signal that the sharks are going after in addition to the chum.

Mike enters the water. Dr. Gruber insists that it will be ok because the sharks want food and Mike is not food to them. Mike still does not want to do this. They have Mike throw a hand grenade as they're surrounded by dozens of hungry sharks. Surprsiingly the repellent works and the sharks scatter immediately. Despite that, Mike wants to get the heck out of the water.

Finally, Mike meets Raj, a professional shark spotter back at False Bay, South Africa. He uses powerful binoculars to watch for sharks from a shack high above the bay. He protects the people who are swimming down below. The minute he sees a shark, the beach is cleared. Raj thinks that he's seen several hundred sharks since he's started working as a spotter.

A white flag with a black shark goes up to warn swimmers when a shark is spotted. A siren activated by Raj also goes off for a minute and a half. Raj won't let Mike touch the siren. The spotters are up there because a woman named Tanya Webb died from a shark attack in False Bay in 2004. The work these spotters do is in honor of her.

It's a great responsibilty to do this job. Mike wants to at least provide Raj with a more comfortable chair, but Raj says he's not up there for comfort. He doesn't want to get to relax and lose concentration which could be very irresponsible and dangerous.