Showing posts with label sharks. Show all posts
Showing posts with label sharks. Show all posts
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linda
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Flying gurnard. Credit: cralize via Wikimedia Commons. / Spotted eagle ray. Credit: john norton via Wikimedia Commons. / Green sea turtle. Credit: Mila Zinkova via Wikimedia Commons. / Weedy sea dragon. Credit: Richard Ling (Rling) via Wikimedia Commons. / Lionfish. Credit: Jens Petersen via Wikimedia Commons. / Cuttlefish. Via. / Icefish. Credit: Uwe Kils via Wikimedia Commons. / Humpback whales. Via. / Hammerhead shark. Via. / Manatee. Via. / Sea lions. Credit: NOAA. / Manta ray. Via. / Flying fish. Via.
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linda
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| Catshark egg casings. Credit: OpenCage.info via Wikimedia Commons. |
The fascinating deep-water cold-seep worlds of mud volcanoes and methane seeps are powered by the process of chemosynthesis not photosynthesis—a difference that gets them branded as 'extreme' environments.
But it turns out that cold seeps are also fantastically rich nursery grounds for deep-water sharks—specifically for catsharks, Galeus melastomus—and for skates—possibly of the genus Bathyraja.
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| Glass skatefish, Bathyraja transpicia. Credit: Sergio Gabriel Nahk via Wikimedia Commons. |
The authors of a new paper in MEPS (Marine Ecology Progress Series) found living egg casings at two modern sites:
- the North Alex Mud Volcano in the eastern Mediterranean Sea, at water depths of about 500 meters/1,640feet
- the Concepción Methane Seep Area in the south-east Pacific Ocean, at depths of about 700 meters/2,300feet
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| Close-up photograph of the tubeworm Lamellibrachia luymesi from a cold seep at 550-meter/1,800-foot depth in the Gulf of Mexico. Credit: Charles Fisher via Wikimedia Commons. |
They also found evidence in the fossil record at the Bear River Cold-Seep Deposit in the North Pacific off Washington that cold deep-water ecosystems have been important to elasmobranchs for at least 35 million years:
[W]e collected 30 fossilized shark egg capsules and fragments thereof. All of the capsules were found closely associated with abundant remains of bathymodiolin mussels, hexactinellid sponges, and tubeworms... The most similar extant egg capsules to those found at the BRSD are those of the deep-water catshark Apristurus spp.
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| Spongehead catshark, Apristurus spongiceps. Credit: NOAA Ocean Explorer. |
As to why some sharks and skates lay their eggs in deep-water cold seeps—and have done so for so long—the authors suggest:
- that coral reeflike marine life in chemosynthetic ecosystems provide holdfasts for egg capsules—on tubeworms, gorgonians, and sponges, and between carbonate boulders
- that enhanced currents around the reefs provide ventilation important for the development of the egg capsules
What's not yet known is the role—if any—that seeps play in the ecology of the hatchling sharks and skates:
We do not know if the seep biostrome is still of importance for the neonate and juvenile sharks and skates after hatching because we could not confirm their presence in the vicinity of the egg capsules. Neonate catsharks and skates are reported to leave their nurseries, probably to escape predation, and to migrate into deeper or shallower depths until they return for mating. However, the seep biostrome could provide ample and localized food sources in the form of small fishes, crustaceans, mollusks, and annelids.
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| Black catshark, Galeus melastomus. Via. |
The authors conclude that 'extreme' seeps are hardly isolated from the 'non-extreme' waters around them:
By serving as nurseries for deep-water marine predators, cold seeps are important components of deep-sea ecosystems and should not be considered as only extreme and exceptional habitats; their presence or absence is likely to influence faunal diversity along continental margins.
The paper:
- ♥ Treude T, Kiel S, Linke P, Peckmann J, Goedert JL (2011) Elasmobranch egg capsules associated with modern and ancient cold seeps: a nursery for marine deep-water predators. Mar Ecol Prog Ser 437:175-181. DOI:10.3354/meps09305
♥ Open access.
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linda
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| A whale shark tilts upright and yanks on a net, trying to make off with a fisherman's catch. Credit: ©Michael Aw/National Geographic. |
An amazing National Geographic photo essay in the October issue—due on newsstands 27 September—tells of the novel relationship between whale sharks and fishermen off Papua, Indonesia.
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| Vying for position under a feeding platform, male whale sharks—two of about twenty that visit this spot—scramble for a snack. Credit: ©Michael Aw/National Geographic. |
Normally these 50,000-pound/22,680-kilogram behemoths are tough to find. They cross ocean basins and can dive more than a mile/1.6 kilometers deep. Some travel to Australia's Ningaloo Reef for the annual coral spawning—a feast for filter feeders. No one yet knows where they mate or give birth.
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| Sarmin Tangadji, the Papua police officer who escorted the photographic team to where the sharks congregate, was so excited to see them up close that he jumped in. Credit: ©Michael Aw/National Geographic. |
Whale sharks also gather off Papua, where artisanal fishermen—hoping to keep their nets and catches intact—offer the whale sharks food.
From the National Geographic article Sharing With Sharks:
Whale sharks are ordinarily loners. But not in one corner of Indonesia. The photographs on these pages, shot some eight miles off the province of Papua, reveal a group of sharks that call on fishermen each day, zipping by one another, looking for handouts near the surface, and nosing the nets—a rare instance when the generally docile fish act, well, like the rest of the sharks.
You can see all the images and read the photo essay here.
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linda
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| Cookiecutter shark. Via FMNH. |
*Warning: graphic images below.*
Ouch. All bite and no bark. The first ever recorded instance of a human bitten by a cookiecutter shark is described in a paper now online in early view in Pacific Science.
An unfortunate human swimmer on a 47.5 kilometer/29.5 mile haul across the Alenuihaha Channel between the Hawaiian islands of Hawai‘i and Maui got nailed twice by this fearsomely ninjalike denizen of the deep, Isistius sp.
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| Two cookiecutter shark bites in a pomfret. Credit: PIRO-NOAA Observer Program via Wikimedia Commons. |
If you've spent any time at sea outside polar waters, chances are you've seen the toothwork of this gnarly little predator. It leaves deep round scars on whales, dolphins, tuna, billfishes, squids, and other larger marine life.
As Kramer used to say: Nature, she is a mad scientist... and never more so than with the hunting technique devised by the cookiecutter shark. Here's how FishBase describes it:
The cookie cutter shark has specialized suctorial lips and a strongly modified pharynx that allow it to attach to the sides of it prey. It then drives its saw-like lower dentition into the skin and flesh of its victim, twists about to cut out a conical plug of flesh, then pull free with the plug cradled by its scoop-like lower jaw and held by the hook-like upper teeth.
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| Cookiecutter sharks live in the mesopelagic zone and below and swim to the surface to feed at night. Credit: Nicholas Felton via Mother Jones. |
Cookie cutter sharks spend the daylight hours below the cusp of darkness—that is, below 1,000 meters/3,280 feet. They migrate to or near the surface at night, travelling 2,000-3,000 meters/6,560-9,840 feet on a diel cycle. That's nearly two miles a day for a fish that maxes out at 56 centimeters/22 inches in length.
They ascend and descend alongside a massive community of marine life known as the deep scattering layer. (I wrote extensively about this community in my Gulf of Mexico oil piece in Mother Jones last year called The BP Cover-Up.)
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| Scars on a dead Gray's beaked whale, Mesoplodon grayi, possibly from cookiecutter shark bites. Credit: Avenue via Wikimedia Commons. |
But here the mad-scientist design gets even madder. The skins of cookiecutter sharks glow strongly bioluminescent—reported to radiate light for as long as three hours after death—part of their underwater camouflage wherein they hide among schools of glowing squid.
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| Bioluminescent squid. Via. |
The human swimmer off Hawaii was attacked at night when the stern deck lights from the escort boat were lit and shortly after the escort kayak lit red and green bow lights. Here's what the Pacific Science paper says:
About ten minutes after the kayak's bow light was turned on, the victim was bumped by a squid. Over the next twenty minutes he was bumped by squid two or three more times in the shoulder and side areas at irregular intervals. At 2003 hrs, the victim suddenly felt a very sharp pain on his lower chest, and assumed it was a triggerfish bite. The sensation was instantaneous and localized, like a pin prick, and felt like a bite from a very small mouth. The victim yelped and swam over to the kayak, turned off the bow light, and was in the process of getting into the kayak with his legs vertical and "egg-beatering" to maintain position when he felt something bite his left calf. The time interval between the two bites was less than 15 seconds. The sensation of the bite to the leg was slightly more prolonged (but still very quick, less than a second), involved some pressure, and was less painful than the chest bite.
After extensive surgery, the deep leg wound was plugged, grafted, and healed. You can read the whole paper and see more images here.
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| Top photo: shallow chest wounds. Bottom photo: deep calf wound. Credit: Honebrink, R., R. Buch, P. Galpin and G. H. Burgess. Pacific Science. |
Not dangerous to people because of its small size and habitat preferences.
The Pacific Science paper concludes:
Humans entering pelagic waters at twilight and nighttime hours in areas of Isistius sp. occurrence should do so knowing that cookiecutter sharks are a potential danger, particularly during periods of strong moonlight, in areas of manmade illumination, or in the presence of bioluminescent organisms.
