Lantern sharks in danger


This video is about a rare frilled shark off the coast of Japan.

By Jennifer Viegas, Discovery News:

Glow-in-the-Dark Sharks at Risk?

July 17, 2007 — One of the first ever detailed studies on deep water lantern sharks, so named for their ability to glow in the dark, has found they are in danger of extinction.

Recent studies have linked declines in shark populations to the collapse of entire marine ecosystems. The loss of lantern sharks could devastate other ocean life globally, as many lantern sharks have wide ranges.

Researchers focused on one species in particular, the smooth lantern shark, commonly caught as by-catch in Portuguese trawling and longline fisheries. Since the bioluminescent shark has little commercial value, the fishermen usually just discard it.

“What we now know is that this species has a vulnerable life cycle characterized by slow growth rates, low fecundity and late maturity,” lead author Rui Coelho told Discovery News.

“When fisheries mortality increases, the populations start to decline and cannot compensate for this,” added Coelho, a shark researcher at the University of Algarve, Portugal.

He and colleague Karim Erzini analyzed 614 by-catch sharks over a two-year period. Their measurements showed the species grows anywhere from 5 to 19 inches long.

The sharks have special light-producing organs, called photophores, mostly found on their sides.

“These photophores may be used to allow individuals to escape from predators, approach prey without the sharks being detected or for species recognition, such as during the mating season,” explained Coelho.

The scientists developed a unique way to determine the age of the sharks: The inner portions of their spines grow continuously. By counting growth bands in this spinal area, similar to counting tree rings, the researchers could estimate each shark’s age.

Their findings have been accepted for publication in the journal Fisheries Research.

The oldest male they found was 13 years old, while the oldest females were 17 years old.

Eggs found within females numbered, on average, 10.44. Since this shark’s reproductive cycle may last as long as three years, the birthrate is extremely low when compared to most other animals and fishes. The researchers also noticed that many females miscarried — likely due to stress — when they became by-catch.

Prior studies conducted by Coelho and Erzini suggest that a number of strategies can reduce by-catch and help prevent lantern shark populations from declining further.

Since the sharks often swim in very deep water, the researchers suggest that fishermen remove hooks from their gear at these levels. For deep water trawling, rigid grids may help to keep fish out of desired crustacean catches.

Laws, such as one that now prohibits trawling in the Mediterranean at depths deeper than 3280 feet, might also afford some level of protection to the sharks and other deepwater species.

A glow-in-the-dark shark scares off predators with “lightsaber-like” spines on its back, a study suggests. The research was carried out on the velvet belly lanternshark, a small species found in the deep waters of the Atlantic Ocean and Mediterranean Sea: here.

Shark research and anglers: here.

Shark fin soup here.

7.5-inch Great Swallower Fish Dies While Swallowing 3-foot Snake Fish: here.

John Paxton from the Australian Museum in Sydney says scientists have found a large school of spawning lantern fish, which have never been seen in Australian waters: here.

Deep-Sea Lanternfish Eat Tons of Plastic: here.

7 thoughts on “Lantern sharks in danger

  1. 08-09-2011 15:33

    Glowing shark wears ‘Cloak of invisibility’since 75 mil. years ago

    The first detailed study of the rare splendid lantern shark reveals that not only does it glow in the dark, but the light effects create a “cloak of invisibility” that helps shield it from predators.

    The study, accepted for publication in the Journal of Experimental Marine Biology and Ecology, is also the first to document the cylindrical-shaped shark’s presence in waters around the Okinawa Islands of Japan, the Discovery News reported on Aug. 3.

    Previously, the shark was only confirmed to exist in the East China Sea, off Taiwan, and in the waters around southern Japan.

    Its natural light show, produced by light-emitting organs called photophores, serves many functions. The cloak of invisibility is perhaps one of the most beneficial, since it helps to protect the small, shark from upward-looking predators. The lantern shark is a member of the small dogfish sharks.

    “The photophores replace the down-welling light from the sun, which is absorbed by the shark’s body,” lead author Julien Claes explained to Discovery News. “The silhouette of the shark therefore disappears when seen from below.”

    Claes, a postdoctoral researcher in the Catholic University of Louvain’s Marine Biology Lab, and colleagues Keiichi Sato and Jerome Mallefet collected, and maintained in captivity, three specimens of the splendid lantern shark.

    Analysis of the sharks revealed that each had nine distinct luminous zones where light was emitted. Some of these zones, such as one on the belly, contribute to the “cloak of invisibility” effect. Other, even brighter, zones are present on the shark’s sexual organs, flanks, tail and pectoral fins. The researchers suspect these are probably used during schooling and sexual communication.

    “Sharks use internal fertilization, so the presence of photophores on the sexual organs may facilitate mating,” Claes said. “Moreover, it might also be a way for the sharks to signal that they are ready to mate or that they are a better candidate for reproduction in a light-induced sexual selection system.”

    The scientists believe nerves and hormones primarily control the light, with pigments also moving in cells as part of the process.

    The luminescence likely evolved when lantern sharks colonized the deep sea probably during the end of the Cretaceous, 65 to 75 million years ago. The splendid lantern shark to this day lives 656 to 3281 feet below the water’s surface, an area with extremely low light levels.

    Claes and his colleagues previously studied another member of this shark family, the velvet belly lantern shark. Both this and the splendid lantern shark share similar luminous zones and other features. It’s therefore probable that their ability to glow evolved long before their clades split up at least 31.55 million years ago.

    It’s even possible that many other prehistoric marine animals could glow in the dark.

    “Unfortunately bioluminescence is a soft-tissue phenomenon that leaves no, or extremely few, fossil tracks,” Claes said. “It is therefore very difficult to establish if a lot of prehistoric animals were luminous, but it is probably the case at least in the deep sea, since bioluminescence is currently widespread in this environment.”

    Nicolas Straube, a researcher at the Bavarian State Collection of Zoology, told Discovery News that he “fully agrees” with the new paper’s conclusions.

    Straube explained that this latest study supports previous theories about lantern shark evolution and luminescence, given both the similarities and differences between the two best-documented species: the velvet belly lantern shark and now the splendid lantern shark.

    At least 33 species exist in this diverse shark family, however, so much remains to be discovered about these dwellers of the ocean depths.

    http://www.koreatimes.co.kr/www/news/tech/2011/08/325_92438.html

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