Today’s fish of the day is Isistius brasiliensis, the Cookie-cutter shark.
Found throughout the world’s deep oceans and growing to only 50 cm long, this tiny shark packs a surprisingly nasty set of teeth. It can open its jaws almost 90 degrees forming its mouth into a suction-cup. Though no-one has ever actually seen the cookie-cutter feed, it is suspected of causing the strange circular bites which have caused damage to a wide range of marine inhabitants including whales, seals, dolphins, large fishes, great white sharks, people and even nuclear submarines! The distinctive, round, gouge-like bite marks have been found on the neoprene sonar-absorbent coating of submarines.
How do we suspect that this tiny shark is the culprit of these strange bites marks? Well, plugs of flesh have been found digesting inside the stomachs of these sharks which match the shape of the gouges taken out of their victims.
In addition to a wicked set of jaws, the cookie-cutter shark is also highly bio-luminescent, meaning that it glows in the dark. It is reckoned that this glowing behaviour may help attract large animals towards it which may then surprisingly be attacked by the tiny cookie-cutter.
This broadbill swordfish with what look to be two distinctive cookie-cutter bite marks in the right hand side was recently landed in Lakes Entrance, Victoria by a recreational fisher. SETFIA members do also occasionally also come across evidence of the bite marks from these wicked little sharks on large fishes they catch.
For more information watch BBC’s video on Cookie-cutter sharks on YouTube.