NORWALK, Connecticut -- The culprit was gravel, that much is known. But the method of ridding the sharks of their once-mysterious lumps has become its own mystery.
For eight years, curators at the Maritime Aquarium at Norwalk pondered the cause of the protuberances on a few of their sharks' underbellies. They weren't pregnant, as visitors often suspected; they were male.
Aided by a few curious local veterinarians and their high-tech imaging equipment, about six months ago the aquarium staff determined that the sand tiger sharks were ingesting gravel from the tank's bottom. After making some phone calls, the staff learned this activity was unique to their sharks. So they were on their own in trying to change the sharks' behavior.
Since the gravel does not appear to hurt the sharks, the curators said, no quick fix was needed. Still, though, the aquarium would prefer to exhibit its most mesmerizing animals without bulges, which detract from the sharks' graceful and aerodynamic figures.
"It's more of an aesthetic issue than a health issue," said Jack Schneider, the aquarium's curator and education director. "Besides, we don't want people to think we have a pregnant shark, especially the males."
So for the past few months, Schneider and his staff have tested various strategies to banish the lumps, with mixed success.
First, they placed a Fiberglas grate over the tank's bottom, which allowed the rays sharing the Open Ocean Tank with the sharks and other fish to suction food from the bottom while -- theoretically -- preventing the sharks from scooping up gravel. The lumps remained.
Then they moved one of the two sharks with the lumps out of the main tank and into an outdoor holding tank that has no gravel. The other shark with the lump stayed in the Open Ocean Tank, but got fed less frequently -- from daily to two or three times a week.
"That made for fewer opportunities for the shark to go to the bottom and forage," Schneider said.
The lump in that shark disappeared. But, as Schneider noted, that shark's lump of gravel has randomly appeared and disappeared over the past eight years. "So whether it was causative or incidental, we're not sure," he said. "But the good thing is that its stomach has gone down to normal."
Nothing has changed, however, for the shark in the gravel-less tank, which has confounded the staff. If the lump is caused by eating gravel, then removing gravel from the shark's environs would, presumably, result in the shark passing it from its system.
"That was the hypothesis we were working under," Schneider said, "but that's not the case."
Tim Gagne, the aquarium spokesman, said the animal husbandry staff will continue to seek creative solutions, but since the animal does not appear to be in distress, they have the time to be deliberate and thorough.
In the short-term, the shark will likely be returned to the exhibit tank. "Moving it doesn't have a downside," Schneider said.
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