Sharks play an essential rol in the health of our oceans

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The cookiecutter shark – a real cookie monster

The cookiecutter shark (Isistius brasiliensis) is named after the cookie-shaped wounds it leaves on its prey. It has lips that resemble suction cups and 25-31 large triangular teeth in the lower jaw as well as 30-37 small teeth in the upper jaw. The teeth are interconnected at the base and therefore are lost as a complete unit rather than just one teeth, as is common in other sharks.

The stomach of this shark also contributes to this sharks’ unique feeding method. It contains a network of light producing organs called photophores that produce a green glow, with a dark patch resembling a smaller fish. This lures fish from the depths and will get bitten by the shark once they get too close. The cookiecutter shark will attach itself to the fish with the sucking lips and pointy upper teeth, creating negative pressure by retracting its basihyal (tongue) and closing its spiracles (small holes in the side of the head that allows water flow into the mouth). Then the shark spins its body and removes a large cookie-shaped piece of flesh from the fish with the serrated bottom teeth. The prey is left with a cookie-cutter shaped hole in the side of its body on average 5 cm wide and 7 cm deep.

Round scars on the flank of a stranded female Gray’s beaked whale (Mesoplodon grayi), probably from cookie-cutter shark bites.

The cookiecutter shark is known to attack large fish such as marlin, wahoo, tuna, sharks and stingrays, as well as marine mammals and reports even exist of them leaving crater marks on the sonar domes of submarines! Until recently, no reports existed of attacks on humans, however in 2011 a marathon swimmer doing a 33-mile swim got bitten by one while he was swimming in a bait ball at night time.

 

Mark Spalding after meeting a cookiecutter shark

 

 

 

 

 

 

See a cookiecutter shark swimming:

Text: Dorien Schröder, Dorien@Dutchsharksociety.org

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