Cookie Cutting Submarines
In our most recent episode on sharks, I briefly touched on the cookie cutter shark (Isistius brasiliensis), and I mentioned they have bitten chunks out of submarines before. So, I figured for the next free post, we'd take a deep dive (pun intended) on these weird little sharks.
A cookie cutter shark (Isistius brasiliensis) compared to a pencil.
They're a deep-sea species known for its distinctive feeding habits. Named for the characteristic, round scars it leaves on its prey—resembling the marks left by a cookie cutter—the shark is relatively small, typically growing to around 20-24 inches (50-60 cm) in length. They're also the most bioluminescent shark there is (see below). Although they can be found in water all around the world, we know very little about them.
On the left you can see the bioluminescence of the cookie cutter shark.
The cookie cutter shark is best known for its unusual feeding mechanism: It uses its specialized, serrated teeth to remove plugs of flesh from its prey in a manner akin to taking a core sample. This feeding method is highly effective in the deep-sea environment where these sharks reside, allowing them to target large animals like fish, squid, and even marine mammals. This feeding method allows them to inflict a precise, circular wound that minimizes the effort required for feeding while maximizing the amount of tissue consumed. A recent 2021 study found, using eDNA (we'll talk about that in an upcoming bonus forensics episode!), that their most common prey are small creatures like squid and crustaceans that live in deeper waters, but they'll supplement those animals with bites from larger things like whales, seals, and occasionally...Submarines.
One of the earliest documented cases of a cookie cutter shark bite on a submarine occurred with the USS Jacksonville, a U.S. Navy submarine, during the 1970s. Crew members noticed peculiar, round scars on the submarine's hull during routine maintenance. These marks were initially baffling, as they did not match the usual damage caused by collisions or underwater debris. After careful examination, it was determined that these circular wounds were the result of a cookie cutter shark's bite. This finding was significant as it was one of the first instances of a cookie cutter shark interacting with a human-made object. Throughout the 70s, 30 more submarines were targeted by these sharks, some cases even going as far causing damage to their neoprene-covered sonar domes, which caused the sound-transmitting oil to leak out and rendered the subs effectively 'blind'. Initially, it was thought there was an unknown weapon being used by the Russians to attack the United States' submarines, but the Navy came to find out that the Russians were having the same problem. Since then, the Navy has prevented this from happening again by installing a protective fiberglass shield over the neoprene covering of the sonar domes.
But just because the Navy made some changes doesn't mean the bites stopped there. In the 1980s, the USS Thomas A. Edison, another U.S. Navy submarine, reported similar incidents: During a deep-sea patrol, crew members discovered circular bite marks on the submarine’s hull. These marks were consistent with those made by cookie cutter sharks. The bites were not severe enough to compromise the submarine’s integrity but were a point of concern for the crew and a topic of interest for marine biologists studying the species.
A more recent case occurred in the 2000s with the USS Virginia, a modern Virginia-class submarine. During routine inspections, crew members found several circular scars on the submarine's hull, which were later identified as the result of cookie cutter shark bites. This case highlighted the ongoing nature of such interactions and the ability of these sharks to adapt to new objects in their environment. It also drew attention to the need for submarine designers to consider potential encounters with marine life in the design and maintenance of their vessels.
And then, in 2003, the British submarine HMS Tireless, while operating in the Arctic region, also reported finding circular bite marks on its hull. These marks were analyzed and identified as being consistent with the feeding patterns of cookie cutter sharks. The incident was notable for its occurrence in a region where cookie cutter sharks are not typically found, suggesting that there is much more to learn about these sharks.
So why do they bite submarines?
Cookie cutter sharks may mistake submarines for potential prey due to their shape or material, leading to these unusual encounters. The sharks are highly adapted to their deep-sea environment, and the presence of large, dark objects like submarines can attract their curiosity. It seems that these instances of them biting submarines is mistaken identity, like we so often see in shark attacks. But how incredible that they can take a chunk out of a submarine, right?
