I went out on my dock yesterday to see if it was good sailing weather, and was surprised to see a bonnethead shark swimming around and around, in that typical lazy way that everything down here in Key West moves.
This bonnethead shark was narrow, and about three feet long, which is a common size. It was a light tan color. Viewed from the side, it has the common shark look, and when it's dorsal and tail fins broke the surface of the water it illicited a strange fear reaction. Jaws taught us that sharks are killers, after all. As he swam under my dock I could see the odd shovel shaped head. A friend of mine caught one while fishing once, so I can tell you that they are tough hombres, with thick skin and surprising strength for their size.
But enough personalizing, let's talk about some bonnethead shark facts.
Bonnethead sharks are of the hammerhead shark family, with a smooth, rounded head. They are a timid shark, with only one incident of attacking a human on record. They migrate only enough to stay in warmer waters, but can be found as far North as New England, and as far South as Brazil, in both the Atlantic and Pacific waters.
Their diet consists of mostly small crustaceans such as the blue crab. Younger bonnethead sharks prefer shrimp. Like most sharks, they are also an opportunistic feeder, so squids, mollusks and small fish are in their diet. Examinations of bonnethead sharks stomachs commonly find seagrasses. Some speculate that the seagrasses are eaten to provide padding so the crustacean shells do not damage the gut, but it could also be that the seagrasses are accidentally devoured as the bonnethead captures its prey. Sharks vomit by turning their stomachs inside out through their mouths, so what they have eaten can be studied without injuring the shark.
Bonnethead sharks must swim continuously. The forward motion causes their gills to open. If they stop swimming, they sink to the bottom and suffocate.
Bonnethead sharks use cerebrospinal fluid, or "CI-excess" to let other sharks know they are in the area.
The purpose of the shovel shaped head is still arguable, but it does at least serve a purpose in holding small prey to the ground as a cover. Also, the shape of the head can provide some degree of hydrofoil, or lift, effect.
A female bonnethead shark in the Henry Doorly Zoo in Omaha gave birth sometime around January 11, 2002, with no access to a male within the last three years. This was widely publicized as a "virgin birth". It is speculated that the female might have been fertilized while still too young to ovulate, and simply carried live sperm inside her for three years, until old enough to give birth. DNA tests are currently ongoing to determine which of the three female sharks gave birth, and perhaps find a clue to who the father is.
Species Name: Sphyrna tiburo
Common Name:(Bonnethead Shark)
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