The year was 1991. The company I worked for was repairing hydrostreamers being used in the Gulf of Mexico. The cables
are quite long, and are towed behind seismic survey boats. We began seeing a lot of cables coming in with very odd damage to the plastic skin. This skin, by the way, is very tough. It's hard to cut with a knife, and hard to puncture. Since these cables are used in the oceans, we've seen many kinds of damage. I've seen cables obviously bitten into by sharks. I found a shark's tooth at one time. Cables get torn on reefs and oil rigs. I still have a tooth that probably belonged to a seal at one time, that I found in another cable. The damage on this occasion, however, was something we'd never seen before. or, if we had, we'd assumed it was something else. Although there was some variation in the marks, there were enough similarities between them to show that they probably had a common source. These two images are of what I'd call the "classic" damage mode.
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All images on this page were taken 01/29/2001, but all of these are samples that I saved from back in 1991. There weren't any digital cameras even close to affordable that long ago. The following images show further examples of the damage we encountered. Most of them are in pairs, showing two views of each cut.
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The holes definitely looked like something had made them, instead of being the result of being dragged across an object. Also, the serrated nature of the cuts was interesting to me. Notice the peculiar scratches on the top surface of the flap above. These marks occur in other examples as well.
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The hole shown in the two views above was a rare occurrence--that of an entire plug pulled out. The image above right,
however, was another type. There was a small subset of these marks that showed this definite "v" shape, as opposed to the circular shape shown in the first two images at the top of the page. Another example is shown below.
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And then, finally, two more images of a "classic" cut in the skin. Those little scratches, or nicks directly opposite the cut are evident here, as well.
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So, we kept getting these sections in at the latter part of 1991. Then, in one of those flashes of inspiration that doesn't happen enough. An image popped into my mind of a book I'd looked through maybe a year or so before. I went back through all the bookstores I could think of (this is where I probably would have seen it.), and I finally did find the image. This was on page 27 in the hardcover book, "Sharks--Silent Hunters of the Deep" ((C)1987 Reader's Digest Services ISBN 0 86438 014 3). The image was actually a small sidebar on that page, and it referred to what is called a "cookie-cutter shark". The sidebar mentions an incident where the US Navy encountered strange damage on their rubber-covered listening devices. There were two photos. One was of a very nasty-looking sharp-toothed critter (which looked nothing a shark); and the other was of the damage done. A crescent-shaped tear in the rubber. Bingo! I knew I'd found the culprit.
Chances are good that as you read this, you are shaking your head, thinking I'm writing another joke. Well, when I went back to work and told my theory to my boss, his boss, and my coworkers, they didn't really believe me, either. We didn't have the access to information that the internet gives us now (Imagine that! Just 9 years, and look what we can find now!). Well, there was nothing for it but for me to buy the book, and show everyone. Then, a fax was sent to the Gulf of Mexico Fishery Management Center, after some other people made some phone calls. The image below left was the part of the fax that was sent. The image below center was the first reply. Then, someone involved in all this-I'm not sure who- contacted Dr. Jose Castro, at the Southeast Fisheries Center. The image below right was his reply. He was also kind enough to fax some pages from his book, "The Sharks of North American Waters" (Texas A+M University Press). Later, I sent him a few samples of the skin, and also, a video tape I'd taken of the majority of the samples. (Have I mentioned that having a digital camera can really make life easier?) I've just had an email correspondence with Dr. Castro, and got his permission to credit him here. So, thank you Dr. Castro, for sharing your knowledge. (What can I say? I doubt that all scientists would take the time to talk to me.)
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So, just what is a "cookie-cutter" shark? Well, I'll paraphrase from the books I've mentioned above . From these sources, I gather that there are actually 2 species of "cookie-cutter". The first is Isistius Braziliensis; and the second is Isistius Plutodus. The first half of the name refers to Isis, the goddess of light, since both of these sharks glow. These sharks get no longer than 50 cm long (around 20 inches). They are generally moderate to deep-water sharks (depending on the species), and Braziliensis is thought to make a daily migration of 1 mile--that is up and down. Nothing "cookie-cutterish" in all of this, is there? Well, now comes the good part. The lower jaw of these sharks contains huge teeth, that are, in effect, joined into a single curved structure. This looks exactly like a cookie cutter (well, one with really nasty points.). It gets even more interesting, though. What these sharks do, is swim up to larger animals (sharks, whales, seals, dolphins, tuna, etc.). Then, the shark latches on with its suckerlike mouth, and twists until it pulls off a circular plug of flesh (remember the hole in the cable skin above?) very much like a cookie-cutter would do. These sharks are poorly built as swimmers, at least compared to the predators that they seem to attack. It has been conjectured that the the cookie-cutter shark's luminescence actually acts as a lure. Then, when the larger predatory species doesn't find food (Who knows? Perhaps the shark can "turn off" its light. I'm guessing, here.), and passes by, or turns away, the cookie-cutter makes its move.