Do Sharks Make Sounds?
In response to a question about whether or not sharks make any sounds, I wrote:
Pioneer undersea explorer Jacques Cousteau called the ocean realm the "Silent World", but nothing could be further from the truth. Whales sing haunting songs, dolphins yap and click, snapping shrimps crackle like castanets, and teleost fishes produce all sorts of grumbles, burbles, grunts, croaks, buzzes, and clicks. But, although they are very much attuned to this great oceanic opera, sharks are — by and large —the quintessential silent hunters.
Unlike their noisy neighbors, sharks have no organs for producing sound. Even their scales are modified to allow them to slip through the water in ghost-like silence. But there are persistent reports from New Zealand of a type of shark that actually barks like a large dog. It's called the Draughtsboard Shark (Cephaloscyllium isabellum), and among New Zealand fishermen it is well known for its sound-producing proclivities. But no one knows for sure how, exactly, these sharks manage to bark. I'd like to propose the following theory:
The Draughtsboard Shark is a member of the same shark genus that includes the Balloon and Swell Sharks. Like its close relatives, the Draughtsboard Shark can inflate itself like a pufferfish when threatened by a potential predator. If attacked underwater, any of these sharks can rapidly pump water into the forward portion of its stomach, increasing the fish's diameter up to three times. Water is prevented from exiting the stomach by a ring of muscle called the cardiac sphincter. The sudden increase in size is enough to startle or intimidate most would-be predators. After the danger has passed, the inflated shark relaxes its cardiac sphincter, allowing the gulped water to gush from the stomach and out the mouth.
But, if caught by net or hook and line and rapidly hauled to the surface, a Draughtsboard Shark may sometimes inflate with air instead of water. The cardiac sphincter renders the Draughtsboard Shark's stomach reasonably air-tight. But when the inflated shark must relieve that gastric pressure, the cardiac sphincter functions in a way that may be termed less-than-refined. When the sphincter relaxes, trapped air passes out the shark's stomach in an explosive rush, creating a hoarse 'bark' as it goes.
So, at least one shark, the inflatable Draughtsboard Shark from New Zealand can produce sound. But I think there's something deeper here. Many people admire sharks because, no matter what they're doing, they look so cool doing it. But no matter how cool they are, even sharks are not immune to the occasional noisy belch.
Thanks for your question, and bon appetit!