Thursday, March 19, 2009

Old hook probable cause of shark death.


You never forget the first time you dive into the Tennessee Aquarium’s Secret Reef exhibit, especially if you have not had the rare open-water diving experience of being surrounded by large sharks. The sandbar and sand tiger sharks at the Aquarium are big and fierce-looking when viewed through the acrylic separating "their world" from "ours." So when I bent over in the water with my dive gear on to peer into the giant tank that very first time, a shiver went down my spine as I looked down just beyond my scuba fins to watch an eight-foot long shark easing past my feet. I thought, "What have I gotten myself into?" Since then, I have learned to appreciate the awesome nature of these creatures. Their special adaptations, how their bodies function, their role in the ocean, and most importantly, how they are NOT eating machines that will go out of their way to harm people. I marvel at the way they move, but still respect the toothy grin that leads their way. Looking into a sand tiger's eyes while in "their world" still quickens the pulse a little bit. So I felt some sadness at last Tuesday night's maintenance dive when I learned that the Aquarium's female sand tiger had died the night before.

The Aquarium has a wonderful living collection of animals big and small. Each species with varying degrees of life expectancy. And, like each of us, every animal is an individual within a species. Some will outlive others.

Many of the animals at the Tennessee Aquarium have a unique story. So here's what we know about this particular shark:

This animal was collected, with the other sand tiger sharks in the Secret Reef, off the coast of Ocean City, Maryland in the summer of 2004. The collector uses specific hooks and techniques to ensure the animal will be healthy and robust once it is placed on display. Before the sharks came to Chattanooga, they were visually inspected to make sure they were in good condition and ready for transport. All of the animals made the journey in fine shape. The sharks were introduced to the Secret Reef in late spring of 2005, prior to the opening of Ocean Journey. The female sand tiger shark weighed 268 pounds at that time. All of these animals have been eating well and acting normally while patrolling the waters of the Secret Reef. The sharks in the Secret Reef are fed on Mondays, Wednesdays and Fridays. Normally, each shark will eat about two to four pounds of fish during these feedings. All of the animals including the female sand tiger ate normally on Monday, March 9th. In fact, she ate two fish that day and appeared to be doing well.

Later that evening, during a routine check, someone noticed the female sand tiger at the bottom of the tank. Husbandry staff and the Aquarium's veterinarian were contacted right away. The husbandry staff donned scuba gear and brought the shark up into a shallow holding tank, but the shark died in spite of this rescue attempt.

A necropsy was performed to try to determine what caused the animal's death. And during the course of this post-mortem examination, a six-inch long stainless steel "J" hook with heavy monofilament leader was found in her stomach cavity. Some of her digestive tract and vital organs were scarred from the movement of this hook through her system over years. There was also signs of infection. Tissue samples were sent off to labs for additional analysis to determine whether or not any other conditions contributed to this shark's death.


It is difficult to know the exact age of a shark, but Aquarium experts estimate this animal was between the ages of 13 and 16. Studies have shown that sand tiger sharks have average life spans between 15 and 20 years in the open ocean.

Many shark species are amazingly resilient when they are injured. And this animal's ability to live with a hook inside her stomach for nearly five years (at least) is testament to that resilient nature. Had the hook been made out of metal rather than stainless steel, it might have dissovled over the course of that many years, but no one knows for sure.

We can also speculate that because commercial fishing for sand tiger sharks has been prohibited where this shark came from, it's possible that she was hooked and brought up alongside a fishing boat where a fisherman recognized the animal as a protected species, then cut the line to let her go with the hook. Again, no one will know for sure.

When this animal died, she weighed 252 pounds. All of the other sharks in this group have gained weight on exhibit.

There are four sand tigers and two sandbar sharks in the Secret Reef today. Tuesday night, I was a diver once again in "their world" helping to clean the exhibit. I was once again captivated by watching the sharks pass nearby or overhead. Flashes of light caught my eye as visitors snapped pictures of the animals from the other side of the acrylic. Today I observed them from "our world" among the Aquarium visitors and marveled at how many digital images were being captured of the sharks on cameras and cell phones. When visitors quiz the Aquarium's docents or volunteer divers during the interactive dive shows, they ask really good questions about these animals. By providing the answers and presenting these animals in the proper context, our visitors learn to appreciate these animals and their role in the natural world.


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