Cookiecutter sharks prefer Swordfish

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Parasitic Cookiecutter sharks seem to prefer biting chunks from Swordfish as opposed to other species.

According to the results of a study by US biologists, parasitic Cookiecutter sharks, Isistius brasiliensis, preferentially attack Swordfish, Xiphias gladius, over other pelagic fish.

Experts from the University of Hawaii, the University of Rhode Island, the Monterey Bay Aquarium and California State University studied bite scars left by Cookiecutter sharks on fish landed at the Honolulu Fish Auction.

The results showed that 25% of Swordfish examined had scars from previous Cookiecutter shark bites, compared to 8.3% of Opah, Lampris guttatus, and much lower numbers for other pelagic fishes.

More bites than other fish

The findings, which have just been published in the journal Environmental Biology of Fishes, also state that most fish have just one Cookiecutter shark bite per individual.

However, Swordfish, often had more than five bites each, as well as a higher proportion of healed scars from previous shark attacks.

The study's authors, Yannis Papastamatiou, Brad Wetherbee, John O'Sullivan, Gwen Goodmanlowe and Christopher Lowe wrote: "Seasonal changes in the probability of hooked fish being bitten by sharks were apparent for Swordfish, Bigeye Tuna and Opah.

"Based on bite scar diameter, larger Cookiecutter Sharks may preferentially attack Swordfish rather than the other species of pelagic fish."

Bites left by a Cookie cutter shark

Daily migrations
Prior to the study, little was known about its feeding behaviour, but it's been reported to have taken chunks out of a range of things, including fishes, marine mammals, squid, human corpses and even inanimate objects such as submarines and undersea cables.

The Cookiecutter shark, Isistius brasiliensis, is a small dogfish-sized shark and is found in warm oceans across the globe.

The species often lives in deep waters and has been recorded as deep as 3.7km/2.3 miles down.

Every day, the Cookiecutter shark migrates vertically through the water column to feed on large pelagic fishes at night. As the sun rises in the morning, it descends into the depths.

The authors claim that their study also adds weight to the vertical migration hypothesis.

"When taken in conjunction with diving behavior of pelagic fish, and fishing depths, the results add further support to the hypothesis that Cookiecutter Sharks perform diel vertical migrations," they added.

Cookiecutter shark factoids
1. Cookiecutter sharks get their name from their characteristic circular bite marks, which resemble the cuts left by a cookie cutter.

2. Cookiecutters have a dark collar-like marking around the head, which is believed to mimic the silhouette of a fish, allowing them to creep up on potential victims.

3. Shipwreck survivors have reported small, deep, clean bites after being attacked in the water at night. Several post-mortems of human corpses have also revealed bites by Cookiecutter sharks.

4. Cookiecutter sharks are luminescent and glow green for several hours after being removed from the water. Their glowing body is believed to attract victims.

5. They reach sexually maturity at just 36-39cm/14-15" long and give birth to 6-12 live pups.

6. Cookiecutter sharks have caused problems for the US Navy several times. In the 1970s, it is claimed that the US Navy believed that enemies had a new weapon that they were using against its submarines. They later learned that the neoprene covered sonar domes had been attacked by Cookiecutter sharks.

For more information see the paper:  Papastamatiou YP, Wetherbee BM, O'Sullivan J, Goodmanlowe GD and CG Lowe (2010) - Foraging ecology of Cookiecutter Sharks (Isistius brasiliensis) on pelagic fishes in Hawaii, inferred from prey bite wounds. Environmental Biology of Fishes, 10.1007/s10641-010-9649-2.