Cookiecutter sharks, deep-sea fish that are often seen only at night, are very rare and difficult to find. We don't know much about cookiecutter sharks as a result.
But if we have one thing to say, it is that they love to bite.
Over the years scientists have discovered tiny, cookie-cutter-shaped pieces taken from the bodies of whales and great white sharks as well as military submarines and humans.
Many scientists have concluded that these tiny predators (Isistius Brasiliensis), usually less than 50cm (1.5 ft) in size, prefer to eat larger prey. However, this is not always true.
"The paradigm was that sharks would prey on larger animals. But we didn't have any empirical data. Our question was "Are we biased by the evidence we see?" Aaron Carlisle, a University of Delaware marine scientist, explains.
(JSUBiology/Flickr/CC BY 2.0)
New research has revealed the contents of the stomachs of 14 cookiecutter sharks. The specimens were taken near Hawaii.
Contrary to our expectations, they tend to pick on prey of their own size. Researchers say that marine mammals and large fish make up less than 10% of the cookiecutter's diet in this area of the globe.
Moreover, only the most powerful cookiecutters eat whales, dolphins, and other sharks that frequent shallower waters. The majority of other cookiecutters were deep-sea dwellers, where they ate small amounts of prey such as cephalopods and crustaceans.
Carlisle says that these animals play a unique ecological function in the oceans of the world.
They eat everything, from the most powerful predators such as white sharks and orcas to the smallest critters. It's rare to find an animal that does something like this.
Female elephant seal bitten by a cookiecutter shark. (JSUBiology/Flickr/CC BY 2.0)
Prior to this study, less than 150 cookiecutter stomachs had been analyzed. Technology has advanced a lot in the past few years.
Many cookie cutters are found without food, but modern biochemical tracing can show what isotopes and fatty acids were absorbed into the water by other animals.
Three of the sharks that were collected did not have any food in their stomachs and even those who did had some, it was very limited. A series of biochemical tests was able to reveal the possible diet of the 14 sharks.
Cookiecutter sharks eat far less large prey than previously believed, according to the stable isotopes and fatty acids as well as environmental DNA found in their guts.
Their prey consists of more than half small animals from deep sea and mesopelagic zones.
Although the study's sample size is very small, it does suggest that cookiecutter diets might be more diverse than we thought.
Their desire to eat certain species seems very flexible. This could be due to the fact that prey moves and sharks grow bigger.
(NOAA/Wikimedia commons)
Cookie cutters can only chase larger, faster-moving prey with bigger fins.
"The little guys, we believe that they may remain down deep. Carlisle says that it appears they don't rise to the surface until they reach a certain size.
"But again, we don't know much because nobody has ever seen a baby Cookiecutter shark. These inferences are based on indirect metrics about what they eat and their ecology.
Scientists still ponder over the latest results. More data will be needed to learn more about these deep-dwelling parasites.
Scientific Reports published the study.
