Midwife to a Tiger Shark

01 November 2018

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Pregnant tiger shark

I could see a shadow in the sea 20 yards away. It was big enough to be mistaken for a large patch of turtle grass on the seafloor or, perhaps, the beginnings of a reef. The Caribbean Sea glowed turquoise blue and the sun made patterns that shifted and danced across the floury white sand on bottom. The water was so clear the surface seemed like an undulating pane of glass. The depth was only 8 feet and you could see every detail in the marine world below—like looking into a gorgeous aquarium.  As I motored closer the shadow morphed into a very large shark...

Initially, I worried it was too big for us to handle. I drove an 18-foot Boston Whaler with two Earthwatch volunteers on board. A big shark in a fighting mood could capsize a small boat. It was the summer of 1988.  I worked for Dr. Samuel H. Gruber of the Rosenstiel School of Marine and AtmosphericScience in Miami and Dr. John F. Morrissey, who, at the time, was a Ph.D. candidate conducting field research on the activity space parameters, home range, diel activity rhythms, and habitat selection of juvenile lemon sharks, Negaprion brevirostris.

I lived on North Bimini with Dr. Morrissey and spent my days running an age and growth study. We’d set a horizontal long line, half a mile in length with 30 hooks, in the waters east of Bimini, on the edge of the Grand Bahamas Bank. Every day I’d drive out to sea to check the longline and re-bait the hooks in the afternoon.  Whatever sharks I caught, we measured, injected with tetracycline hydrochloride,tagged at the base of the dorsal fin, and then released. The tetracycline hydrochloride injection was an intramuscular shot that would incorporate into the shark’s vertebral column and be used as a time marker in age and growth studies in the event of future recapture.

Releasing a shark was easier said than done. It usually required getting into the sea and swimming around with the shark and driving ocean water through its gills until the predator revived. I’d hold the shark’s left pectoral fin in my left hand and put my right arm across its back, almost affectionately, like a young man on a movie date with his girlfriend. Once you swam forward and gathered a little momentum, the shark’s extraordinary aerodynamic shape made lifting even the largest and heaviest shark manageable. Initially, they were often lifeless and somewhat rigid. After a few minutes of swimming, one could feel energy start to animate a shark’s body.  The tail would begin to wave left and right, subtly at first, then stronger and stronger, until the fish was able to swim on its own. Then I let the shark go free.

Some were very large predators: bulls, great hammerheads, tigers, lemons, and the occasional Caribbean reef shark. All of these species reach a good size and have the teeth necessary to cause a fatal injury. Every one of them would have been justified in attacking me - after all, I had hooked them in the mouth, suffocated them by preventing them from swimming properly, injected them with a drug, and then stabbed them in the back to insert a tag. Yet, despite these provocations, the sharks almost always peacefully swam off. I doubt they feel emotion, but sometimes I had the sense that they felt relief as they swam away from me. During my time as a shark researcher, I caught virtually every coastal species of shark common in the Caribbean Sea and snorkeled with hundreds of them.

A Magnificent Female

As I motored closer, the contours of the shadow became clear enough to identify the species: a massive tiger shark. It looked like a torpedo with fins but with the bulk and power of a small diesel pickup truck. It lay motionless on the white sand bottom, except for the opening and closing of its mouth, ventilating its gills. I put the engine into neutral and carefully pulled in the line hooked to its lower jaw. The long line was rigged for small to medium-sized sharks, not giants. The rope was frayed and almost broken—the shark had nearly busted free. Any serious run by the great fish would snap the line. Anxiously, I continued pulling in the rope, as gently as possible, until I could feel her on the other end. Suddenly the shark began to swim, rising off the seafloor,growing bigger and bigger, and more formidable, fanning her tail side to side. The long line allowed her to move back and forth in a semi-circle by the side of the Whaler. That's when I got my first true look at her.

She was absolutely magnificent, a beautiful female. She moved through the glowing water with sinuous sweeps of her tail and the sun played across her dark grey back. Somehow, the bait, a large barracuda’s head, dangled from the corner of her mouth, still attached to the hook—a gruesome trophy that stared with dead, hollow eyes. The tiger shark tried to swim away and pulled the frayed line taught, almost snapping free. I nearly stopped breathing. Then she felt the pull of the hook and settled down in the sand again. Her breaking the line seemed inevitable. If I could catch her, it would be thehighlight of the summer.

Natural History

The tiger shark was first described scientifically in 1822 by Peron and Lesueur and named Squalus cuvier for the great French anatomist Georges Cuvier. During the almost 150 years that followed, eight additional names were given to this species. Today, the tiger shark is recognised as a single, worldwide species, Galeocerdo cuvier. It is distinguishable from other sharks by its large size (rare specimens have measured 18 feet in length) and striking colour pattern, which in the young consists of vertical black spots and bars. These marks merge and fade in larger specimens and are absent in adults. The teeth of tiger sharks are uniquely shaped and, unlike many other shark species, are similar in both the upper and lower jaw. Every tooth is serrated like a steak knife for shearing the flesh of prey. Tiger sharks are the most feared shark in the Caribbean and in French Polynesia. The species is second only to the white shark (Carcharodon carcharias) in confirmed unprovoked attacks on humans and boats.

Tiger sharks have been subjected to great commercial fishing pressures. Products from this species include its liver, which contains high concentrations of vitamin A-rich oil, its hide, which has 6 to 10 times the tensile strength of oxhide, and its fins, which are used to make soup. However, like most other species of sharks, the tiger shark is extremely susceptible to overfishing, primarily due to its humanlike life-history strategy. Like us, sharks mature late, live long lives, and produce relatively few young for a fish.

Perhaps, more than any other shark species, the feeding habits of the tiger shark have done more to perpetuate the myth that all sharks are swimming garbage collectors. The "Catholic diet" of the tiger shark led one researcher to speculate that this species has perhaps the least specialised diet of all sharks. Certainly, its feeding behaviour is nearly legendary. Items found in the stomachs of tiger sharks include all types of marine reptiles, various marine mammals, grass, carrion, dogs, marine and terrestrial birds, cows and horses (presumably from local slaughter houses), fish, conch, sharks, cephalopods, billfish, and an amazing variety of inedible junk including nails, wood, tools, tar paper, and even an unopened can of salmon.

When examining the stomach contents of tiger sharks around Bimini, we found an impressive variety of edible items including birds, stingrays, gastropod mollusks, lobsters, and fish, but no inedible trash. The actual occurrence of garbage in the stomach of any shark species is very rare. In our research experience, only two sharks examined had non-prey items in their stomachs, the strangest being a tiger shark that had an empty birth-control-pill container in its stomach. This shark was caught by a sportfisherman off the coast of New York, and it was not pregnant!

A Pregnant Giant

The moment I looked at the tiger shark underwater I suspected she was pregnant.  Her belly was swollen to an enormous size. Either she’d eaten something like a whole manatee or she was approaching the full term of a pregnancy. Afraid she would snap the frayed line if I tried to pull her to the surface again, I donned my mask and snorkel and quietly slipped into the sea and swam down to her. I had brought a tail rope. Normally, I didn’t tail rope sharks until we pulled them to the surface because sometimes they thrashed and snapped their jaws to get free. It could get dangerous. I wanted to catch this shark so badly I was willing to take risks I normally wouldn’t. Like Bilbo stealing gold from the dragon Smaug in J.R.R. Tolkien’s The Hobbit, I sneaked up and discreetly tail roped her underwater,gently tightened the noose, and got out of the sea.

Up Out Of The Water

When we started pulling in the tail rope the shark exploded to life. She thrashed and churned the waves for a couple of minutes. Then she did something I’d never seen before. The sea was only 8 feet deep and later, when we measured her, we learned she was almost 13 feet long. Somehow she pushed off the bottom with her tail and, for a crazy moment, stood up out of the water. Her head was broad and blunt, her jaws enormous, and at the height of her effort, she seemed to stand taller than the crew in the Whaler.

She came towards us, all power, teeth, and attitude, like she might come across the boat. We moved back in fear. Then she crashed sideways into the sea with an enormous splash. The Earthwatch team pulled the tail rope tight and tied it to the stern cleat. Then we tied the line hooked to her mouth to the forward cleat. She slammed her tail into the side of the Whaler making the boat lurch and shudder. After a few moments she grew calmer and, finally, idle, alongside the boat. She measured 12.5 feet in length and 5.5 feet in girth. She was the largest shark I caught that summer.

Giving Birth

Earlier, I had used the Walkie-Talkie to call Dr. Morrissey and told him I might have caught a pregnant tiger shark. He raced out to meet us in a separate boat and brought his underwater camera. We went back in to the sea and inspected the shark. Fetal membranes protruded from her vent. She was definitely pregnant and may have already released some pups—possibly due to the stress of capture. Tiger sharks are ovoviviparous and hatch from a thin egg case while still in the mother and then are born live.

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Assisting a tiger shark to give birth

When I first touched the pregnant tiger shark near her vent, she reacted violently and slammed her tail against the Whaler. After some gentle coaxing, she permitted me to help in the birthing process. The first baby measured 32 inches in length. It came out fully formed with striking blue eyes, unlike adults of the species. Eventually and sadly, the pup died despite efforts to swim it through the water. Two more pups were birthed and also soon died. The pups were apparently premature and the mother was aborting them as a result of the stress of capture. Estimating that there were as many as 60 more pups in her belly, we quickly decided to release her before she lost any more babies. We untied her tail and removed the hook from her mouth. She’d been in the water the entire time and did not need to be revived.

Underwater, I watched her go free. For an eerie moment she glanced at me with one of her flat, dark eyes, and I wondered what she thought. Then she swam off into the hazy blue distance, propelling and gliding her giant body through the sea, heading towards deeper water and the Gulf Stream beyond. She didn’t seem in a rush and didn’t seem particularly bothered; she just cruised away in a sort of nonchalant, business-like manner. Then again, how can one truly read a shark?

 

The author of this article, Howard Butcher, has also recently published his first novel, Jonah: A Novel of Men and the Sea


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Jonah: A Novel of Men and the Sea

 

 

Comments

Incredible! What a read!

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