Cookiecutter shark

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For other species of cookiecutter sharks, see Isistius.

Cookiecutter shark
side view of a slender brown shark with small fins and large green eyes, with a pencil alongside to show that it is of small size

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Subdivision: Selachimorpha
Order: Squaliformes
Family: Dalatiidae
Genus: Isistius
Species:
I. brasiliensis
Binomial name
Isistius brasiliensis
(Quoy & Gaimard, 1824)
world map with blue areas scattered through the Atlantic, Indian, and Pacific Oceans, excluding the polar regions
Range of the cookiecutter shark
Synonyms

Isistius labialis Meng, Chu & Li, 1985
Leius ferox Kner, 1864
Scymnus brasiliensis Quoy & Gaimard, 1824
Scymnus torquatus Müller & Henle, 1839
Scymnus unicolor Müller & Henle, 1839
Squalus fulgens Bennett, 1840

The cookiecutter shark (Isistius brasiliensis), also called the cigar shark, is a

caudal fin. It is dark brown, with light-emitting photophores covering its underside except for a dark "collar" around its throat and gill slits
.

The name "cookiecutter shark" refers to its feeding method of gouging round plugs, as if cut out with a

undersea cables, and human bodies. It also consumes whole smaller prey, such as squid. Cookiecutter sharks have adaptations for hovering in the water column, and likely rely on stealth and subterfuge to capture more active prey. Its dark collar seems to mimic the silhouette of a small fish, while the rest of its body blends into the downwelling light via its ventral photophores. When a would-be predator approaches the lure, the shark attaches itself using its suctorial lips and specialized pharynx and neatly excises a chunk of the flesh using its bandsaw-like set of lower teeth. This species has been known to travel in schools
.

Though rarely encountered because of its oceanic

fisheries
.

Taxonomy

French

Egyptian goddess of light.[4][5]

One of the earliest accounts of the wounds left by the cookiecutter shark on various animals is in ancient Samoan legend, which held that atu (

parasites.[6][7] In 1971, Everet Jones of the U.S. Bureau of Commercial Fisheries (a predecessor of the National Marine Fisheries Service) discovered the cigar shark, as the cookiecutter shark was then generally known, was responsible. Shark expert Stewart Springer thus popularized the name "cookiecutter shark" for this species (though he originally called them "demon whale-biters").[8] Other common names used for this shark include luminous shark, smalltooth cookiecutter shark, and smooth cookiecutter shark.[9]

Description

The cookiecutter shark has an elongated, cigar-shaped body with a short, bulbously rounded snout. The nostrils have a very short flap of skin in front. The large, oval, green eyes are placed forward on the head, though not so that binocular vision is extensive. Behind the eyes are large spiracles, positioned on the upper surface of the head.

The mouth is short, forming a nearly transverse line, and is surrounded by enlarged, fleshy, suctorial lips. The upper jaw has 30–37 rows of teeth, and the lower jaw has 25–31, increasing with body size. The upper and lower teeth are extremely different; the upper teeth are small, narrow, and upright, tapering to a single, smooth-edged cusp. The lower teeth are also smooth-edged, but much larger, broader, and knife-like, with their bases interlocking to form a single saw-like cutting edge. The five pairs of gill slits are small.[3][5][6]

The

dermal denticles
are squarish and flattened, with a slight central concavity and raised corners. The cookiecutter shark is chocolate brown in color, becoming subtly lighter below, and a dark "collar" wraps around the gill region.

The fins have translucent margins, except for the caudal fin, which has a darker margin.[5] Complex, light-producing organs called photophores densely cover the entire underside, except for the collar, and produce a vivid green glow.[5] The maximum recorded length for this species is 42 cm (17 in) for males and 56 cm (22 in) for females.[9]

  • The cookiecutter shark has a short, rounded head with large, anteriorly placed eyes and a transverse mouth.
    The cookiecutter shark has a short, rounded head with large, anteriorly placed eyes and a transverse mouth.
  • Head
    Head
  • Jaws
    Jaws
  • Lower teeth
    Lower teeth
  • Upper teeth
    Upper teeth
  • Jaw diagram
    Jaw diagram

Distribution and habitat

Inhabiting all of the world's major tropical and warm-

Bahamas and southern Brazil in the west, Cape Verde, Guinea to Sierra Leone, southern Angola, and South Africa in the east, and Ascension Island in the south. In the Indo-Pacific region, it has been caught from Mauritius to New Guinea, Australia, and New Zealand, including Tasmania and Lord Howe Island, as well as off Japan. In the central and eastern Pacific, it occurs from Fiji north to the Hawaiian Islands, and east to the Galápagos, Easter, and Guadalupe Islands. Fresh wounds observed on marine mammals suggest this shark may range as far as California in warm years.[3][5][6]

Based on catch records, the cookiecutter shark appears to conduct a

Euprotomicrus and Squaliolus.[6] It is frequently found near islands, perhaps for reproductive purposes or because they hold congregations of large prey animals.[6] In the northeastern Atlantic, most adults are found between 11°N and 16°N, with the smallest and largest individuals being found in lower and higher latitudes, respectively.[10] There is no evidence of sex segregation.[11]

Biology and ecology

Ventral view of a shark's head with teeth visible in the open mouth
The suctorial lips and large lower teeth of the cookiecutter sharks are adaptations for its parasitic lifestyle.

Best known for biting neat round chunks of

cartilages.[12] With small fins and weak muscles, this ambush predator spends much of its time hovering in the water column.[6][13] Its liver, which can comprise some 35% of its weight, is rich in low-density lipids, which enables it to maintain neutral buoyancy. This species has higher skeletal density than Euprotomicrus or Squaliolus, and its body cavity and liver are proportionately much larger, with much higher oil content.[6][14] Its large caudal fin allows it to make a quick burst of speed to catch larger, faster prey that come in range.[14]

The cookiecutter shark regularly replaces its teeth like other sharks, but sheds its lower teeth in entire rows rather than one at a time. A cookiecutter shark has been calculated to have shed 15 sets of lower teeth, totaling 435–465 teeth, from when it was 14 cm (5.5 in) long to when it reached 50 cm (20 in),[11] a significant investment of resources. The shark swallows its old sets of teeth, enabling it to recycle the calcium content.[6]

Unlike other sharks, the retina of the cookiecutter shark has ganglion cells concentrated in a concentric area rather than in a horizontal streak across the visual field; this may help to focus on prey in front of the shark.[15]

This shark has been known to travel in schools, which may increase the effectiveness of its lure (see below), and discourage attacks by much larger predators.[12]

Bioluminescence

a small shark lying belly-up, with a clear dark brown band around the throat
The dark collar of the cookiecutter shark is believed to act as a lure.

The intrinsic green luminescence of the cookiecutter shark is the strongest known of any shark, and has been reported to persist for three hours after it has been taken out of water.

photophores serve to disrupt its silhouette from below by matching the downwelling light, a strategy known as counter-illumination, that is common among bioluminescent organisms of the mesopelagic zone. The individual photophores are set around the denticles and are small enough that they cannot be discerned by the naked eye, suggesting they have evolved to fool animals with high visual acuity and/or at close distances.[12]

Set apart from the glowing underside, the darker, nonluminescent collar tapers at both sides of the throat, and has been hypothesized to serve as a lure by mimicking the silhouette of a small fish from below. The appeal of the lure would be multiplied in a school of sharks. If the collar does function in this way, the cookiecutter shark would be the only known case of bioluminescence in which the absence of light attracts prey, while its photophores serve to inhibit detection by predators.[12][13] As the shark can only match a limited range of light intensities, it has been suggested that its vertical movements might serve to preserve the effectiveness of its disguise across various times of day and weather conditions.[12]

Feeding

a silvery fish with round concavities gouged from its side
Pomfrets are one of the many species parasitized by the cookiecutter shark.

Virtually every type of medium- to large-sized oceanic animal sharing the habitat of the cookiecutter shark is open to attack; bite scars have been found on

bristlemouths, copepods, and other smaller prey.[11]

beached Gray's beaked whale
.

Parasitic attacks by the cookiecutter shark leave a round "crater wound", averaging 5 cm (2.0 in) across and 7 cm (2.8 in) deep.

beached melon-headed whales with dozens to hundreds of recent and healing cookiecutter shark wounds, while such wounds are rare on non-emaciated beached whales.[22] The impact of parasitism on prey species, in terms of resources diverted from growth or reproduction, is uncertain.[21]

The cookiecutter shark exhibits a number of specializations to its mouth and

electric carving knife.[20] This shark's ability to create strong suction into its mouth probably also helps in capturing smaller prey such as squid.[12]

Life history

Like other dogfish sharks, the cookiecutter shark is

gestation period. The embryos had developed brown pigmentation, but not the dark collar or differentiated dentition. Newborn cookiecutter sharks are 14–15 cm (5.5–5.9 in) long.[23] Males attain sexual maturity at a length of 36 cm (14 in), and females at a length of 39 cm (15 in).[3]

Human interactions

dorsal view of the front part of a small shark
A cookiecutter shark is caught on a longline near Hawaii; large spiracles are located behind the eyes.

Favoring offshore waters and thus seldom encountered by humans, the cookiecutter shark is not considered dangerous because of its small size. However, it has been implicated in a few

Kailua-Kona, Hawaii was bitten on the right foot and calf.[30] In March 2023, Andy Walberer was attacked by two cookiecutter sharks while swimming the Molokai channel. He was able to grab and throw both sharks before serious injury was inflicted.[31]

There are several records of human bodies recovered from the water with post-mortem cookiecutter shark bites.[14][32][33]

During the 1970s, several

Oceanographic equipment and telecommunications cables have also been damaged by this species.[3][18]

The harm inflicted by cookiecutter sharks on

least concern.[1] In June 2018 the New Zealand Department of Conservation classified the cookiecutter shark as "Not Threatened" with the qualifier "Secure Overseas" under the New Zealand Threat Classification System.[36]

References

  1. ^
    doi:10.2305/IUCN.UK.2018-2.RLTS.T41830A2956761.en
    . Retrieved November 12, 2021.
  2. ^ Quoy, J.R.C.; J.P. Gaimard (1824–1825). "des Poissons. Chapter IX". In de Freycinet, L (ed.). Voyage autour du Monde...exécuté sur les corvettes de L. M. "L'Uranie" et "La Physicienne," pendant les années 1817, 1818, 1819 et 1820. Paris. pp. 192–401.
  3. ^
    ISBN 978-0-520-23484-0
    .
  4. ^ Gill, T.N. (1865). "Synopsis of the eastern American sharks". Proceedings of the Academy of Natural Sciences of Philadelphia. 16 (5): 258–265.
  5. ^ a b c d e f Bester, C. Biological Profiles: Cookiecutter Shark Archived April 9, 2013, at the Wayback Machine. Florida Museum of Natural History Ichthyology Department. Retrieved on January 26, 2010.
  6. ^
    ISBN 978-92-5-101384-7
    .
  7. ^ Jones, E.C. (1971). "Isistius brasiliensis, a Squaloid Shark, the Probable Cause of Crater Wounds on Fishes and Cetaceans" (PDF). Fisheries Bulletin. 69 (4): 791–798.
  8. ^
    ISBN 978-0-8117-2875-1
    .
  9. ^ a b Froese, Rainer; Pauly, Daniel (eds.) (2009). "Isistius brasiliensis" in FishBase. November 2009 version.
  10. S2CID 86259333
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  11. ^
    JSTOR 1441272
    .
  12. ^
    S2CID 45347124
    .
  13. ^ a b Milius, S. (August 1, 1998). Glow-in-the-dark shark has killer smudge. Science News. Retrieved on December 15, 2014.
  14. ^ a b c d e f g Martin, R.A. Deep Sea: Cookiecutter Shark. ReefQuest Centre for Shark Research. Retrieved on January 26, 2010.
  15. S2CID 26648368
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  16. ISBN 978-0-12-350403-6
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  17. ISBN 978-0345547118
    .
  18. ^ a b c Martin, R.A. Squaliformes: Dogfish Sharks. ReefQuest Centre for Shark Research. Retrieved on January 26, 2010.
  19. S2CID 86420663
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  20. ^ a b Martin, R.A. Attacked by a Dogfish. ReefQuest Centre for Shark Research. Retrieved on January 26, 2010.
  21. ^
    ISBN 978-0-8493-1514-5
    .
  22. doi:10.1111/j.1748-7692.1996.tb00582.x
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  23. ^
    doi:10.1111/j.1095-8649.2002.tb01723.x
    .
  24. ^ Perry, B. (March 21, 2009). "Cookie-cutter sharks 'sort of a mosquito of the sea'" Archived March 3, 2016, at the Wayback Machine. The Maui News. Retrieved on January 26, 2010.
  25. S2CID 85627382
    .
  26. ^ "Rare Cookiecutter Shark Bite in Hawaii". March 18, 2019.
  27. ^ "Second cookiecutter shark bite reported in Hawaii". April 17, 2019.
  28. ^ "In rare third incident for year, swimmer attacked by cookiecutter shark". November 20, 2019.
  29. ^ McMurray, Kevin (November 1, 2017). "7-year-old bitten by cookiecutter shark in Australia". Tracking Sharks. Retrieved January 18, 2023.
  30. ^ McMurray, Kevin (December 15, 2022). "Man fights off shark attack with diving knife". Tracking Sharks. Retrieved January 18, 2023.
  31. ^ McMurray, Kevin (April 24, 2023). "Hawaiian swimmer fast-pitches attacking cookiecutter sharks". Tracking Sharks. Retrieved April 29, 2023.
  32. PMID 15166773
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  33. PMID 27623973
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  34. ^ Johnson, C.S. (1978). "Sea Creatures and the Problem of Equipment Damage". U.S. Naval Institute Proceedings. August 1978: 106–107.
  35. ^
    ISBN 978-1-60239-021-8
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  36. OCLC 1042901090
    .

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