29 November 2010

A WAVE OF SCIENCE—BUT WHERE'S ADA?


The seventh and latest installment in John Boswell's Symphony of Science. Great, as usual. Though surely he will manage to come up few more women thinkers next time? Twenty-first century, and all that.

(Ada Lovelace, first ever computer programmer.)

The entrenched refusal to acknowledge the many women, past and present, at the forefront of science led in 2009 to the declaration of March 24th as Ada Lovelace Day—an international day of blogging to celebrate the achievements of women in technology and science. Lovelace is today recognized as the world's first computer programmer. From Finding Ada:

Ada Lovelace was one of the world’s first computer programmers, and one of the first people to see computers as more than just a machine for doing sums. She wrote programmes for Charles Babbage’s Analytical Engine, a general-purpose computing machine, despite the fact that it was never built. She also wrote the very first description of a computer and of software.

From Rebecca Thomson at New Scientist's Culture Lab:

Today it's fairly well accepted that women are under-represented in both science and technology fields: for example just one in five of the UK's technology workforce are female.

But the negative nature of the debate, and the complaints raised within it, mean the considerable achievements of women who do work in the industry can slip under the radar. A recent piece by gadget magazine T3 neatly highlighted important contributions to the field made by women largely forgotten.
It included Mary Lou Jepsen, whose work on holographic video systems at the MIT Media Lab and in optics resulted in important developments in the fields.
One of her biggest achievements was her part in the One Laptop Per Child project, which delivered laptops to 1.5 million of the world's poorest children. She helped get the project off the ground by inventing display technology that is readable in sunlight, and working on the power system that made the laptops energy efficient.

Then there's this sadly enlightening piece in last week's The Observer: The Royal Society's Lost Women Scientists.

So how about a Wave of Ada segment to your next movement of the symphony, John Boswell?

28 November 2010

SUNDAY POETRY: "THE LOBSTER"



THE LOBSTER
by Carl Rakosi

Eastern Sea, 100 fathoms,   
green sand, pebbles,   
broken shells.


Off Suno Saki, 60 fathoms,   
gray sand, pebbles,   
bubbles rising.


Plasma-bearer   
and slow-
motion benthos!


The fishery vessel Ion
drops anchor here
                           collecting   
plankton smears and fauna.


Plasma-bearer, visible
sea purge,
                sponge and kelpleaf.   
Halicystus the Sea Bottle


resembles emeralds   
and is the largest   
cell in the world.


Young sea horse   
Hippocampus twenty   
minutes old,


nobody has ever   
seen this marine   
freak blink.


It radiates on   
terminal vertebra   
a comb of twenty


upright spines   
and curls   
its rocky tail.


Saltflush lobster   
bull encrusted swims


backwards from the rock.
(Slipper Lobster larva. Photo by Peter Parks. From the Australian Museum.)

27 November 2010

ENDLESS SUMMER FOR SEABIRDS

(Streaked shearwater. Photo by marj k Marj Kibby, at Flickr.) 

Shearwaters are long-winged, strong-flying seabirds of the open ocean who come ashore only to breed. The rest of their lives—including the time between fledging and sexual maturity, up to 12 years in some species, maybe more—are spent entirely at sea. They're long-lived birds, with reports of one 55-year-old Manx shearwater still breeding in Ireland as of 2003.

Their time aloft and afloat is not without pattern. The more we learn, the more we see how these oceanic travellers follow vast systems of winds and waves across hemispheres and even oceans.

First up, there's an interesting paper out in the current issue of The Auk about a presumed foraging association between streaked shearwaters (Calonectris leucomelas) and skipjack tuna (Katsuwonus pelamis).

Foraging associations—as the term implies—are the result of a follower species (here, the shearwater) commonly following a nuclear species (here, the tuna) to capture prey flushed in the course of the nuclear's feeding or travels. The deep blue home is full of foraging associations... including the way savvy human fishers follow seabirds to find fish.

(Skipjack tuna. Photo JFontes—ImagDOP, from here.)


(Streaked shearwater at breeding colony on Mikura Island, Japan. Photo by Kanachoro, courtesy Wikimedia Commons.)

A little background: Streaked shearwaters breed on the islands and coastlines of Japan, China, and Korea, and make impressive winter migrations (≤5,400 kilometers /3,300miles) to the waters off Vietnam, New Guinea, the Philippines, and Australia.

























(Movement of a streaked shearwater from Japan to the Gulf of Carpentaria, Australia, between 16 October 2004 and 13 January 2005. Figure from Ornithological Science.)

In the figure above you can see the flight of one shearwater between its breeding grounds in the Northern Hemisphere during the boreal summer and its "wintering" grounds in the Southern Hemisphere during the austral summer. Those results are reported in a 2008 paper in Ornithological Science by some of the same members of the shearwater-skipjack team during an earlier phase of study.


(From Ornithological Science.)

In their latest investigations, the researchers attached small global location sensors to 48 breeding birds in 2006, 38 of whom returned the following year with their geolocators intact. Their findings, from the abstract:

Most Streaked Shearwaters wintered off northern New Guinea, an area of low primary productivity but high Skipjack Tuna (Katsuwonus pelamis) abundance. Streaked Shearwaters flew for longer periods and landed on the water more frequently around dawn and dusk during the wintering period. This pattern of activity is similar to that of subsurface predators such as tuna, and to that of tropical seabirds that are known to feed with subsurface predators. We suggest that Streaked Shearwaters probably forage in association with subsurface predators in the tropical oceans during the wintering period. Foraging in association with subsurface predators and morphological adaptations for gliding may allow Streaked Shearwaters to forage efficiently in both temperate and tropical environments.


(You might have to divert here to watch the video.)

This Blue Planet video shows the dynamics of shearwaters (not sure which species) working schools of mackerel herded up to the surface, initially by dolphins, then by skipjacks... I love the way they've mixed shearwater calls into the underwater video—dramatic, but inaccurate, at least to the extent heard here.

(Sooty shearwaters. Photo by marlin harms, courtesy Wikimedia Commons.)

In an incredible piece of scientific detective work a few years back, a different team of researchers found that another species, sooty shearwaters (Puffinus griseus), embarked on remarkable 64,000-kilometer/40,000-mile annual migrations through the entire basin of the Pacific Ocean from Antarctica to the Bering Sea—the longest migration of any animal tracked to that point.

(From PNAS.)

Their map shows the geolocation tracks of 19 of their tagged sooty shearwaters at New Zealand breeding colonies (light blue); their migration pathways north (yellow); and their wintering grounds and southward transits (orange). Figures bd represent the figure-eight movement patterns of individual shearwaters travelling to one of three "winter" destinations in the North Pacific.

The authors suggest the figure-eight  pattern is facilitated by prevailing wind patterns and by the Coriolis effect—which influence the long-range trajectories of the birds as they rocket between hemispheres at rates of up to 910 kilometers/565 miles a day, and as they chase the waves of summer from one hemisphere to the other.

(Credit: NASA/Seasat.)

You can correlate something of the travels of the sooty shearwaters to this map of prevailing winds over the Pacific.

The 2006 sooty shearwater paper appeared in Proceedings of the National Academy of Sciences. From the abstract:

Electronic tracking tags have revolutionized our understanding of broad-scale movements and habitat use of highly mobile marine animals, but a large gap in our knowledge still remains for a wide range of small species. Here, we report the extraordinary transequatorial postbreeding migrations of a small seabird, the sooty shearwater, obtained with miniature archival tags that log data for estimating position, dive depth, and ambient temperature. Tracks (262 ± 23 days) reveal that shearwaters fly across the entire Pacific Ocean in a figure-eight pattern while traveling 64,037 ± 9,779 km roundtrip, the longest animal migration ever recorded electronically. Each shearwater made a prolonged stopover in one of three discrete regions off Japan, Alaska, or California before returning to New Zealand through a relatively narrow corridor in the central Pacific Ocean. Transit rates as high as 910 ± 186 km·day−1 were recorded, and shearwaters accessed prey resources in both the Northern and Southern Hemisphere’s most productive waters from the surface to 68.2 m depth.
But now the flying record of the sooty shearwaters been topped by a diminutive seabird, the Arctic tern, who not only crosses hemispheres but ocean basins as well.


(From PNAS.)

These are the geolocation tracks of 11 Arctic terns tracked from breeding colonies in Greenland and Iceland. The green lines are their autumn postbreeding migration (August–November). The red their "winter" range (December–March). The yellow their spring return migration (April–May). Two southbound migration routes are adopted in the South Atlantic, either (A) West African coast or (B) Brazilian coast. Dotted lines link locations during the equinoxes.

The research is reported in a February 2010 paper in PNAS, revealing migrations for Arctic terns of more than 80,000 kilometers/48,000 miles a year.


(Arctic tern. Photo by Malene Thyssen, courtesy Wikimedia Commons.)

Such globe-trotting transits keep these butterflies-of-the-sea hopped up on the endless summers of the high-latitudes. They barely know night.


The papers:
  • Takashi Yamamoto, et al. At-Sea Distribution and Behavior of Streaked Shearwaters (Calonectris leucomelas) During the Nonbreeding Period. The Auk. 2010. 127 (4) 871–881. DOI: 10.1525/auk.2010.1002
  • ♥ Akinori Takahashi. Post-breeding movement and activities of two Streaked Shearwaters in the north-western Pacific. Ornithological Science. 2008. 7 (1) 29-35. DOI: 10.2326/osj.7.29. ♥
  • Scott A. Shaffer, et al. Migratory shearwaters integrate oceanic resources across the Pacific Ocean in an endless summer. PNAS. 2006. 103 ( 34) 12799-1280. DOI: 10.1073/pnas.0603715103. ♥
  • Carsten Egevang, et al. Tracking of Arctic terns Sterna paradisaea reveals longest animal migration. PNAS. 2010. 107 (5) 2078-2081. DOI: 10.1073/pnas.0909493107. ♥
I ♥ open-access papers.

    24 November 2010

    ILLUSTRATED: THE EKMAN SPIRAL

    (The ocean off Tasmania, Australia. This is an unfiltered false-color MODIS {Moderate Resolution Imaging Spectroradiometer} satellite view designed to enhance the reflections from phytoplankton, dissolved organic matter, sediments, and bubbles in the sea—though it may have also picked up reflections from Earth's atmosphere and even from the spectroradiometer itself. Normally, the MODIS images we see have been filtered clean of most of these data. This unfiltered image gives a sense of the ocean's dynamic complexity. HT Discovery Earth. Credit: NASA/GeoEye.)

    I've been getting feedback from readers of my book DEEP BLUE HOME wishing for photos or illustrations of some of the species and subjects I wrote about. So I thought I'd post some clarification here on the blog.

    First up, the Ekman Spiral, from Chapter 7, "Whorls." Here's the excerpt from the book, now illustrated:

    Upwellings are the most biologically productive of all currents: vertical conveyor belts rising from the abyss to the surface, bearing the sunken components of dead plants and animals in the form of dissolved organic matter. This rich broth is destined to fertilize the phytoplankton in the sunlit zone, whence much of the dissolved organic matter originally came. 

    (Upwelling in the Northern Hemisphere. Image courtesy of Sanctuary Quest 2002, NOAA/OER.)

    Upwellings occur anywhere, including in midocean, though the superproductive ones develop along coastlines, where prevailing winds blow parallel to the shore, pushing the surface waters ahead of them. But because the flow of wind-driven water is also influenced by the Coriolis effect (a spin-off of the Earth’s rotation), the wind-driven current is deflected to the right of the wind in the Northern Hemisphere and to the left in the South. 


    In the image above you can see how the Coriolis effect causes ocean gyres in the Northern Hemisphere to spin in a clockwise direction and those in the Southern Hemisphere to spin in a counterclockwise direction as a result of Earth's spinning rotation.


    (Credit: Eumetsat.)

    The same process drives low pressure storm systems in the atmosphere. You can see a low sweeping across Ireland and Britain in the top of this image, and numerous southern hemispheres lows swirling around Antarctica at the bottom.

    BTW, if you really want to trip out in this image, check out this super high-res close-up of it.

    The Coriolis effect is a deceptively complex process, as you can see when BBC filmmakers spring the question on some unsuspecting experts in the video below.



    Annoyingly, you may have to go here to be amused by this BBC clip.

    Back to the excerpt:

    And because the ocean is stratified into density layers, the Coriolis effect redirects these tiers too. The surface-driven current, spun by the Coriolis effect, tugs on the layer below it, which tugs on the layer below it, to successively lesser degrees. The end result is a downward whorl known as an Ekman spiral, which corkscrews miles below its originator, the wind. The net work of all the layers is known as the Ekman transport, with a theoretical power to deflect water ninety degrees off the wind. 
























    (This schematic shows how ocean currents change direction in relation to the wind direction as a result of the Coriolis effect: (1) wind (2) force of water from above (3) direction of current prior to the Coriolis effect (4) direction of water after the Coriolis effect. Each layer of ocean water exerts pressure on the layer below it and the process is repeated downward. Courtesy Wikimedia Commons.)

    Consequently, breezes blowing parallel to a coastline actually result in water flowing offshore at a right angle. The offshore flow is then replaced by water rising from the deep, bearing its Miracle-Gro of nutrients destined to feed blooms of phytoplankton, which feed zooplankton, who feed the sardines, who feed the tuna, dolphins, whales, and seabirds. The plankters that escape being eaten sink to the seafloor upon death, their ghosts eventually resurrected back to the surface to fertilize their own kind, maybe their own kin, some generations hence. Thus the deep blue home recycles matter and energy with impeccable efficiency. 

    22 November 2010

    BEACH, FIRST DATE


    I've noticed whenever a Vimeo filmmaker gets a new camera or piece of equipment, he or she takes it to the beach—if there's a beach nearby... first date with expensive gear. Lucky for us.
























    (Art: Ruth Eastman. From GlamourSplash... awesome site.)

    21 November 2010

    SUNDAY POETRY: "TOR HOUSE"



     





















    If you should look for this place after a handful of lifetimes:
    Perhaps of my planted forest a few
    May stand yet, dark-leaved Australians or the coast cypress, haggard
    With storm-drift; but fire and the axe are devils.
    Look for foundations of sea-worn granite, my fingers had the art
    To make stone love stone, you will find some remnant.
    But if you should look in your idleness after ten thousand years:
    It is the granite knoll on the granite
    And lava tongue in the midst of the bay, by the mouth of the Carmel
    River-valley, these four will remain
    In the change of names. You will know it by the wild sea-fragrance of wind
    Though the ocean may have climbed or retired a little;
    You will know it by the valley inland that our sun and our moon were born from
    Before the poles changed; and Orion in December
    Evenings was strung in the throat of the valley like a lamp-lighted bridge.
    Come in the morning you will see white gulls
    Weaving a dance over blue water, the wane of the moon
    Their dance-companion, a ghost walking
    By daylight, but wider and whiter than any bird in the world.
    My ghost you needn’t look for; it is probably
    Here, but a dark one, deep in the granite, not dancing on wind
    With the mad wings and the day moon.


    (Robinson Jeffer's Tor House. From the Robinson Jeffers Tor House Foundation.)

    19 November 2010

    MYSTERY OF THE ICE WHALES
























    (The whale within the iceberg. 1884. By George R. Halm. From the New York Public Library Digital Gallery.)

    Believe it or not, whales sometimes end up frozen in glaciers, some of which may then calve out with icebergs to float around the ocean for a spell. 

    The illustration above, by New York artist George R. Halm (1850-1899), tells a visually compelling story—though the words to this tale have been forgotten, as best I can tell.












    So what could the picture be about? Well, the engraving includes images of men at work on the sea. Maybe whalers.









    Handwritten at the bottom of the print is the word "Whaling"—perhaps a catalogue notation from an early librarian.















    The detail in the lower left might be an image of a sunken ship. Maybe a whale-wrecked ship. With nothing left afloat but the crow's nest? I'm not sure. Was there once a story of a wronged whale and a haunted iceberg on an intercept course with a few doomed sailors?

    Moby Dick was published 33 years before George R. Halm's engraving—priming the public mind for tales of vengeful behemoths.



    moby dick intro from Carys Banks on Vimeo.

    Interestingly, in his description about the the blubber of sperm whales, Herman Melville included an eerie reference to ice seamen:

    For the whale is indeed wrapt up in his blubber as in a real blanket or counterpane; or, still better, an Indian poncho slipt over his head, and skirting his extremity. It is by reason of this cosy blanketing of his body, that the whale is enabled to keep himself comfortable in all weathers, in all seas, times, and tides. What would become of a Greenland whale, say, in those shuddering, icy seas of the North, if unsupplied with his cosy surtout? True, other fish are found exceedingly brisk in those Hyperborean waters; but these, be it observed, are your cold-blooded, lungless fish, whose very bellies are refrigerators; creatures, that warm themselves under the lee of an iceberg, as a traveller in winter would bask before an inn fire; whereas, like man, the whale has lungs and warm blood. Freeze his blood, and he dies. How wonderful is it then—except after explanation—that this great monster, to whom corporeal warmth is as indispensable as it is to man; how wonderful that he should be found at home, immersed to his lips for life in those Arctic waters! where, when seamen fall overboard, they are sometimes found, months afterwards, perpendicularly frozen into the hearts of fields of ice, as a fly is found glued in amber.







    For another ice whale story only slightly less mysterious, I found a 1959 paper in Nature, about the 1958 discovery of a whale entombed in a glacial moraine beyond which the glacier had retreated in Svalbard (also known as Spitzbergen), north of mainland Norway.


    (The Isefiorden, Spitzbergen, Norway, c. 1890-1900. From the Library of Congress' Flickr photostream.)

    Disappointingly, I can only read the abstract, since even with my exorbitantly expensive personal subscription to Nature I am not entitled to read back issues from 1959. (O, ♥less policy.)

    The abstract is tantalizing:

    THE preservation of Pleistocene or Recent land mammals in the Siberian permafrost has long been known, but the literature does not appear to include mention of marine mammals preserved in ice. Particular interest, therefore, is attached to the discovery in 1958 of part of a whale carcass entombed in the ice-cored moraine of Sveabreen, Ekmanfjord, in Vestspitsbergen. The north-eastern lateral moraine of Sveabreen projects into the fjord about two miles beyond the ice-front, and the find was made by members of the Birmingham and Exeter Universities Spitsbergen Expedition near the seaward tip.
























    (Bowhead whale. Photo by Ansgar Walk, courtesy Wikimedia Commons.)

     What species of whale was it? Were they able to determine? 

    There was a huge whaling and walrusing industry in Svalbard beginning in 1604—a piratical affair between British, Dutch, Danish, and French mercantile companies, who built forts to defend their commercial interests.

    (Photo from the BBC.)

    Their primary targets were bowhead whales—the real ice whales.


    (The whale-oil factory of the Amsterdam Chamber of the Greenland Company on Amsterdam Island near Spitzbergen. 1639. Cornelis de Man.)

    In 1996 a bowhead whale melted out from another Svalbard glacier, bringing with it a few juicy clues about its past... including a death date circa end of the Little Ice Age... perhaps from the time of the earliest commercial whalers.

    Here's the abstract of the 1997 paper in Polar Research:

    An 8 m long carcass of a bowhead whale (Balaena mysticetus) melted out from remnant glacier ice in the lateral moraine of the Jemelianovbreen glacier in August 1996. Folded and sheared sediment bands in the ice suggest that the whale was incorporated during an advance of the glacier. The whale's longitudinal axis was oriented parallel to the direction of the ice-flow, with the thinnest posterior part dipping upflow. The posterior section was best preserved with muscles and blubber, although the entire skin surface was strongly decomposed and only a thick fibrous surface was left of the blubber. The abdominal wall was holed, most likely by marine organisms, and partly filled with a compacted mixture of well-sorted gravelly beach sediments and fat. the whale seems to have been incorporated into the glacier together with glaciomarine sediments and carried by the flowing ice to an altitude of ca. 15 m. Jemelianovbreen is a tidewater glacier with two known surge-episodes. The first and most extensive of these occurred ca. 1900 AD and reached ca. 7 km outside the present coast-line. Radiocarbon dating of a fragment of a caudal vertebra yielded 345 ± 40 14C years BP (1535-1660 cal. AD), suggesting that the whale lived some time during the last part of the cold period known as the Little Ice Age.

    (Antarctic toothfish, Dissostichus mawson, a Nototheniid. Photo by Paul Cziko, courtesy Wikimedia Commons.)

    Whales aren't the only mysteries trapped in ice. A 1962 paper in the Polar Record recounted all kinds of entombed marine life found by early Antarctic explorers. The abstract:

    In February 1902, members of Scott's Discovery expedition found the remains of a fish 18 in. long on the surface of the "pinnacled ice" near the ice front of the Ross Ice Shelf in McMurdo Sound. In 1903, a party under Wilson found three Nototheniid fishes, sponges, shells, and seaweeds among similar ice on the floating section of the Koettlitz Glacier. The fishes, which were up to 48 in. in length, were all headless. They resembled a specimen caught in a seal blow-hole near the Discovery winter quarters, whose head was bitten off by a seal before it could be landed, but whose body weighed 40 Ib. and was 46 in. long. This fish was a Notothenia, close to N. colbecki Boulenger. In 1911, a party under Taylor found another large headless fish, which may have been as much as 4 ft. long, embedded in the ice of the Lower Koettlitz Glacier some 5 miles from its seaward end, and among the pinnacled ice near the Dailey Islands the same party found corals, shells, sponges, patches of sediment, and about a dozen small fish. The ice in this region was so rich in sponges that it was difficult to get spicule-free ice for cooking.



    (The pinnacled ice of McMurdo Sound, photographed by Reginald Skelton for the British National Antarctic Expedition—aka Scott's Discovery expedition—1901-1904. From the Royal Collection.)

    A news story out of Greenland in 1985 aroused the mystery again, along with a new round of theorizing:
    A dead whale frozen in an iceberg 13 feet above the surface of the frigid waters off south Greenland is mystifying scientists and curious residents of a tiny Greenland settlement. No one can figure out how the 59-foot sperm whale died or how it ended up in an icy grave high above the water drifting a few miles off the tiny settlement of Alluitsup. First came speculation the beast was a prehistoric creature buried for eons in the ice cap that makes up 85 percent of Greenland. But examination showed that the whale, the size of which indicates it was a male, was identical to contemporary sperm whales. And it emitted a rank smell, making fossilhood unlikely... Close inspection reveals the whale may have been the victim of a hunter`s harpoon. In its neck is a cylindrical hole 15 inches in diameter and three feet. But that does not explain how the beast came to rest in an icy grave bobbing 13 feet above the water. One theory is that it sprang into the air and landed unluckily on a large iceberg, perhaps stuck in a narrow crevice. Marine biologists in Greenland theorize the whale may have been attacked by killer whales, or, stranded in a shallow area, became disoriented and died. They believe the whale, weakened or dead, could have drifted over the submerged portion of an iceberg and become an involuntary hitchhiker when the iceberg separated and a submerged portion rose under the whale.


    Cutting Room Floor: "Deep at Sea" from Tristan Bayer on Vimeo.

    (The filmmaker describes: "This cut is made with unused footage that we shot in Dominica which would otherwise be left on the 'Cutting Room Floor.''')

    The papers:

    14 November 2010

    SUNDAY POETRY: "SEA-WARD, WHITE GLEAMING..."


    (Common gull, or mew gull, or sea-mew, or Larus canus. Photo by Tomasz Sienicki, courtesy Wikimedia Commons.)

    by Samuel Taylor Coleridge

    Sea-ward, white gleaming thro' the busy scud
    With arching Wings, the sea-mew o'er my head
    Posts on, as bent on speed, now passaging
    Edges the stiffer Breeze, now, yielding, drifts,
    Now floats upon the air, and sends from far
    A wildly-wailing Note.

    12 November 2010

    THE GREAT EEL QUESTION

    Photo from here.
    Two closely-related species of shapeshifting fish inhabit the North Atlantic: the American eel, Anguilla rostrata; and the European eel, Anguilla anguilla.

    They share a catadromous lifestyle, that is, they live in freshwater but breed in saltwater. That's the opposite of the better-known anadromous fish, like salmon.

    Few animals have eluded human understanding for so long as these eels. For centuries, no one knew that a variety of lifeforms found in both fresh and salt water were members of the same species at different stages of a life history. Here they are:
    • leptocephalus
    • glass eel
    • elver
    • yellow eel
    • silver eel 
    European eel. Photo by Ron Offermans, courtesy Wikimedia Commons.
      
    After lifespans of perhaps 20 years, maybe many more, the Atlantic eels abandon their riverine or shoreside homes and swim back to the Sargasso Sea to spawn. The sexually mature adults, called silver eels, die after spawning. 

    12-day-old larva of the European eel, Anguilla anguilla. Photo by Jonna Tomkiewicz, DTU Aqua.
    In amongst the sargassum, the fertilized eggs hatch into ferocious-looking larvae (above). 

    Photo by Uwe Kils, courtesy Wikimedia Commons.
    A larva of the anguillid eels is known as a leptocephalus. The name's left over from the time (until 1893) when these 5-centimeter/2-inch-long larvae were considered a species all their own: Leptocephalus brevirostris.

    Photo by Uwe Kils, courtesy Wikimedia Commons.
    Leptocephali larvae metamorphose into juveniles, the glass eels, during their first migration, as they drift from their hatching grounds in the Sargasso Sea.

    The postlarval glass eels in the photo above are in the process of transitioning from salt to fresh water. Their skin is still transparent enough that you can see their red gills and hearts.

    Elvers. Photo by Uwe Kils, courtesy Wikimedia Commons.
    As glass eels begin to develop coloration, they become known as elvers. By this stage they've made riverfall in North America or Europe, depending on their species.

    Elvers were favorite foods throughout much of old Europe. In his writings from 1679, the British philosopher John Locke (1632-1704) suggested sampling elver-cakes when visiting Bristol. Perhaps some of the eels' transformational powers rubbed off, gastronimocally speaking, to influence Locke's transformed thinking?

    My OED tells me the word eelet was also used for elver, and that the state of being a young elver was known as elverhood. Good words worth reviving.

    Illustration: Ellen Edmonson and Hugh Chrisp, courtesy Wikimedia Commons.
    The insoluble problem of eels and elvers was outlined in wonderfully antique language in a 1923 paper to The Royal Society.

    We know, then, that the old eels vanish from our ken into the sea, and that the sea sends us in return innumerable hosts of elvers. But whither have they wandered, these old eels, and whence have the elvers come? And what are the still younger stages like, which precede the "elver" stage in the development of the eel? It is such problems that constitute the "Eel Question."

    The great eel question befuddled some notoriously fine minds—including Sigmund Freud, who in his student days dissected hundreds of immature eels in search of their elusive male sex organs.

    Photo by Max Halberstadt.

    He eventually quit the eel business to famously spend his post-elverhood dissecting female minds in search of the equally elusive envy of male sex organs.

    Many years, countless nautical miles, and some finer science minds later, the strange pieces of the anguillid puzzle began to fall into place.

    In 1920, Danish biologist Johannes Schmidt (nicknamed Eel-Schmidt... it was he who posed the "Eel Question" in the 1923 paper, above) discovered that Atlantic eels migrate to the Sargasso Sea to spawn.

    There they join a floating community of life centered around protective drifting forests of sargassum.



    Sargasso Film - Off Nantucket from Eric Savetsky on Vimeo.

    BTW, the sargassum weed in this gorgeous bit of film is probably full of leaf-mimic leptocephali too small and too transparent to easily discern.

    Young eels get caught in the currents swirling around the edges of the ocean gyre that is the Sargasso Sea, and ride with mats of sargassum drifting northward.

    Credit: Jim Gower, Stephanie King, Casey Jones, Institute of Ocean Sciences, Department of Fisheries and Oceans, Sidney, BC Canada. From NASA's Earth Picture of the Day, (EPOD).
    In the image above, you can see a dense concentration of sargassum trapped in a northbound eddy of the Gulf Stream far off New Jersey. This was the first ever sargassum eddy recorded by satellite. From the EPOD caption:

    Here water is shown in blue colors and haze and cloud is dark blue and black. Lighter blue, green and yellow indicate increasing concentrations of weed at the sea surface. The floating weed tends to be concentrated into lines by converging flow. On this day a high concentration of the floating weed has been trapped in a Gulf Stream eddy. Other lines of weed can be seen nearby, stretched along the flow of the Gulf Stream. Satellite data (MERIS Reduced Resolution imagery for 4 Oct 2006) are provided by the European Space Agency—MCI is the Maximum Chlorphyll Index. Our report on the first satellite images of Sargassum weed recorded in the Gulf of Mexico is in press. [I've cited their paper, below.]


    Credit: Uwe Kils, courtesy Wikimedia Commons.
    European eels spawned in the Sargasso Sea migrate on the North Atlantic's currents more than 5,000 kilometers/3,100 miles to Europe (above), where they work their way up river systems. Some swim up underground rivers to populate landlocked lakes. The numbers in the graphic refer to the size of the eels along their migratory route.

    Credit: Uwe Kils, courtesy Wikimedia Commons.
    American eels jump off the currents and work their way inland after shorter migrations (above).

    New research from those eel leaders, the Danes, just published in Proceedings of the Royal Society B, illustrates the great marriage between oceanic currents, sea surface temperatures, and oceanic migrations, and how all work to disperse some leptocephali larvae to North America and others to Europe—even though their larval ranges overlap, at least in small part, in the Sargasso Sea. The same drivers, apparently, drive the two species differently:

    The small spatial overlap implies that a large proportion of larvae of each species could be influenced differently by prevailing hydrography and currents.

    From the abstract:

    Our findings suggest a key role of oceanic frontal processes, retaining eel larvae within a zone of enhanced feeding conditions and steering their drift. The majority of the more westerly distributed American eel larvae are likely to follow a westerly/northerly drift route entrained in the Antilles/Florida Currents. European eel larvae are generally believed to initially follow the same route, but their more easterly distribution close to the eastward flowing Subtropical Counter Current indicates that these larvae could follow a shorter, eastward route towards the Azores and Europe. The findings emphasize the significance of oceanic physical-biological linkages in the life-cycle completion of Atlantic eels.

    Dioarama: Sargasso Sea, floating jungles of the Atlantic, from the Milstein Hall of Ocean Science at the American Museum of Natural History.
    Another paper in the same issue of Proceedings of the Royal Society B, reports the success or failure of nesting loggerhead sea turtles is driven in part by the currents—including some of the same currents utilized by the eels—that sweep past their nesting beaches. From the abstract:
    For marine animals whose offspring must migrate long distances, natural selection may favour reproduction in areas near ocean currents that facilitate migratory movements. Similarly, selection may act against the use of potential reproductive areas from which offspring have difficulty emigrating. As a first step towards investigating this conceptual framework, we analysed loggerhead sea turtle (Caretta caretta) nest abundance along the southeastern US coast as a function of distance to the Gulf Stream System (GSS), the ocean current to which hatchlings in this region migrate. Results indicate that nest density increases as distance to the GSS decreases... Similar factors may influence patterns of abundance across the reproductive ranges of diverse marine animals, such as penguins, eels, salmon and seals. 

    Loggerhead turtle, Caretta caretta. Photo by ukanda, courtesy Wikimedia Commons.
    The new great eel question is all about their decline. There are 90-98 percent fewer European eels now than in the 1970s.

    Might it be these travellers are having a hard time finding their optimal "nesting beaches" amid changing ocean conditions?


    Tale of a bucket with a Tail from 5 Gyres on Vimeo.

    Or might the leptocephali be suffering from the tons of plastic garbage collecting in their birth-gyre in the Sargasso?

    The causes of the eels' decline are manifold and may be as difficult for us to decipher as their beginnings.

    Finally, another new paper in Biology Letters presents findings on the mysterious origins of the anguillid eels... did these species originate in fresh or salt water? From the abstract:

    Of more than 800 species of eels of the order Anguilliformes, only freshwater eels (genus Anguilla with 16 species plus three subspecies) spend most of their lives in freshwater during their catadromous life cycle. Nevertheless, because their spawning areas are located offshore in the open ocean, they migrate back to their specific breeding places in the ocean, often located thousands of kilometres away. The evolutionary origin of such enigmatic behaviour, however, remains elusive because of the uncertain phylogenetic position of freshwater eels within the principally marine anguilliforms. Here, we show strong evidence for a deep oceanic origin of the freshwater eels, based on the phylogenetic analysis of whole mitochondrial genome sequences from 56 species representing all of the 19 anguilliform families.



    May the cycle never end.

    The papers:
    I ♥ open-access papers.