the secret life of eels
TRANSCRIPT
The University of MaineDigitalCommons@UMaine
Maine Sea Grant Publications Maine Sea Grant
3-2016
The secret life of eelsCatherine [email protected]
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Repository CitationSchmitt, Catherine, "The secret life of eels" (2016). Maine Sea Grant Publications. 115.https://digitalcommons.library.umaine.edu/seagrant_pub/115
&MAINEBOATS,HOMES HARBORS
A Truly Tiny Home ✯ The Amazing American Eel ✯ Father-Son Boat Project
+ADVENTURESin a Maine
Peapod
BOATS of theYEAR
2016
Special Section
The Secret Life
40
There’s still a lot to learn about these elusive and mysterious fishBY CATHERINE SCHMITT PHOTOGRAPHS BY HEATHER PERRY
of EELS OTHER MIGRATORY FISH get more atten-tion than the American eel. Salmon is theking of fish; the alewife, the fish that feeds all;
shad, the founding fish. Sturgeon are dinosaurs; smelt,the ice shack fish. Yet, historically, the eel was morewidespread and abundant than any of these in thenortheast United States. The undeserved neglect is like-ly a result of the eel’s snakelike nature, or perhapsbecause more than any other species of sea-run fish, theeel has evaded human explanation and understanding.
And so, around the world, the eel is a metaphor forthe elusive, the slippery, and the mysterious, mostlybecause of its unusual life cycle.
The American eel, Anguilla rostrata, differs from theother migratory or sea-run fish that live in Mainebecause it goes the opposite way: instead of living itsadult life in the ocean and entering fresh water to spawn(a lifestyle scientists call anadromy), the eel hatches inthe ocean, spends most of its life in rivers and lakes, andthen migrates back to sea (catadromy).
Maritime encounters with larval eels, flat and trans-parent willow leaves with teeth, led scientists to narrowdown the eel’s spawning grounds to the Sargasso Sea,an area of the Atlantic Ocean north of Puerto Rico. Thepresumption is that all American eels—the speciesranges from Greenland to Venezuela—travel to the Sar-gasso, which overlaps slightly with the Bermuda Trian-gle. It’s an extraordinary journey, considering the eelsmust retrace the route they took as larvae and, oncethere, die after spawning.
For nearly a century, scientists have searched thesewaters for adult eels. One such researcher, JamesMcCleave, professor emeritus at the University ofMaine, participated in several cruises to the Sargasso,the most recent in 2007. The researchers found noth-ing but floating patches and strands of Sargassum sea-weed. Then, in October 2015, a team of Canadianresearchers (some of McCleave’s colleagues and formerstudents) reported tracking an adult eel—one of sev-eral dozen affixed with satellite tags—from Nova Sco-tia to Bermuda, the first hard evidence of the eelmigration. One tagged eel, the only one that survived,traveled 1,500 miles in 45 days in pretty much astraight line.
41
Eels begin their lives in the Sargasso Sea and then migrate to theeastern coast of North America as leptocephali—clear and flattenedand very small. When they get the first hints of fresh water, theybegin to transform into the glass eel stage. At this point they are2 to 3 inches long, the thickness of spaghetti, and clear as glass.This photo was taken at the mouth of a creek in Boothbay Harbor.
While spawning activity remainsundocumented, larval eels appear in theocean currents in and around the Sar-gasso. After making a genetic note abouthow to get back someday, baby eels ridethe Gulf Stream north.
They spend about a year in the drift,somehow crossing the Gulf Stream andfinding their way into the Gulf of Maine.During that time they transform intotwo- to three-inch long glass eels thatcan swim upstream through estuaries(moving upstream with each flood tide,mostly at night). A darker, brownish-green color and four or so inches long,at this phase they are known as elvers. InMaine, this migration occurs betweenMarch and June, triggered by spring’swarming temperatures and high riverflows that carry the scent of land. Thoseelvers that escape the nets of commercialfishermen (see sidebar) grow into adultyellow eels. At this stage, the eels becomemale or female, a differentiation influ-enced by the environment. In southernareas where warm temperatures lead to
faster growth and where densities of eelsare higher, more become male. Males aresmaller. A northern clime, and lonely butclean headwaters and remote lakes, favorthe female tendency. Northern femalesare also larger.
At some point, after at least six yearsand perhaps as long as thirty, the yelloweel is ready to migrate back home to theSargasso and mate. It changes coloragain, turning metallic black-yellow,with thick skin and large eyes to facilitatemigration. These adult eels, now knownas silver eels, leave their freshwaterhomes in fall and make their way back tothe Sargasso.
It is not known how eels determineexactly where to stop and find a mate.According to James McCleave, there is“an idea that some oceanographicfrontal regions, where temperature andsalinity changes, might serve as oceano-graphic signals—a feature that eelsmight detect. Multiple researchers havefound lots of larval eels in and near thesefronts.”
42 MAINE BOATS, HOMES & HARBORS | March / April 2016 | Issue 139
Yellow eels are the freshwater life stagebetween elvers and reproductive adults. These
were filmed late at night in an algae bloomon the Sebasticook River in Winslow.
Migrating ever upward, mostly at night,adolescent eels can even climb dam walls.
Reprinted with permission of MAINE BOATS, HOMES & HARBORS • DIGITAL edition @ www.maineboats.com 43
As with salmon and shad, the eel’smigratory habits are affected by humans.Hydroelectric dams are particularlydamaging, as adult eels are killed orinjured as they move through turbines.Fishing and habitat loss, parasites, andpollution are additional threats. Theirlong life and tendency to accumulate fatmakes eels vulnerable to heavy metalsand other toxic chemicals that build upin body tissue over time.
The International Union for theConservation of Nature has placed theAmerican eel on the “red list” of endan-gered species. Several citizen-driven peti-
tions to designate the eel as endangeredin the United States so far have failed.
EMILY THORNTON, a first-year Ph.D.student at the University of Maine, hasbeen working with fish biologist JosephZydlewski to study eels in Maine rivers.In the fall of 2015, they set up a weir inSouadabscook Stream, a tributary of thePenobscot River, to trap migrating eels.They tagged the eels, and put them inthe Penobscot River above Milford Damto test how and whether they getthrough the dam safely.
The tags transmit signals to an
array of hydroacoustic buoys placedthroughout the river. The same buoysare used by multiple agencies andresearchers to track salmon, sturgeon,and other fish. “We don’t have a good,consistent idea of how these fish makeit through various hydro projects,”said Thornton. While she is looking atsurvival specifically at Milford Dam,which is now the first/last dam on thePenobscot, Thornton said that whatthey can learn about migration wouldbe applicable to fisheries managementthroughout the region. “If we canidentify migratory cues like how
THE SECRET LIFE OF EELS
Adult eels once were a popular food source for ancestors ofthe native Wabanaki people, who fished for eels with spears,weirs, and woven baskets or pots, primarily in fall and win-ter. An eel weir in Sebasticook Lake dates back 5,000 years.Major eel fisheries took place at Kenduskeag and Passad-umkeag streams in the Penobscot watershed. European set-tlers recognized and quickly began taking the eel, a favoreddelicacy from their side of the pond.
According to the Maine Department of MarineResources, Maine’s eel harvest peaked in the early 1900s.Though populations have declined, those looking to fish foreels (defined by the state as larger than nine inches) for per-sonal consumption can take “up to 25 eels per day from thecoastal waters of the state by spear gun, harpoon, pot, orhook.” A special eel license is required for commercial fish-ing, which is done only with eel pots (traps).
However, the majority of commercial fishing takes placefor the juvenile elvers (defined by the state as an Americaneel that can pass through a 1/8-inch-mesh net). Caught withhand-held dip nets and funnel-shaped “fyke” nets anchoredto river banks, elvers are sold to dealers in Asia, where theyare placed in constructed ponds and raised to adulthood forthe seafood market. While most stay in Asia (Japan even hasa traditional eel-eating holiday), there is a chance the “unagi”you enjoy at a sushi restaurant started its life in the SargassoSea, traveled to Maine, grew up in China, and was shippedback to Maine in a frozen package. Declines in Japanese andEuropean eel species, disruption of the Japanese eel indus-try due to the 2011 tsunami, and popularity of sushi have allcontributed to higher prices for Maine elvers ($900 a poundin 2011; $1,800 in 2012; $2,500 in 2015). High prices led toa “Wild West” scenario in the Maine fishery for several years,until the state implemented license and harvest restrictions,swapped cash for a credit card-type payment system, andcracked down on poaching and other criminal activity.
Despite elvers being a relatively “new” fishery in Maine(since the 1970s), there is something fitting about seeingnets in the rivers, and watching men and women work themidnight shores by lantern-light, making a living from whatthe sea offers. —CS
These glass eels have been harvested and are awaiting transport to Asia,where they will be grown to market size. They were photographed in an eelbuyer’s holding facility in Woolwich, Maine.
MAINE’S LUCRATIVE ELVER FISHERY
many are leaving, and when, theremight be implications for manage-ment.” For example, if scientists findthat most of the eels leave on a fewnights with certain conditions (rain,high-flowing rivers, new-moon dark-ness), managers can shut downhydroelectric turbines on those nightsto spare the eels.
Thornton said that eels are “incred-ibly slimy, really agile” and “tough towork with.” They can move forward andbackward. It’s hard to get them to liestraight for measuring. They can swimout of buckets and slither over land.
Eels from the Penobscot Riverdemonstrated this skill in November,when they moved through the rainy
streets of downtown Bangor. Accordingto the Bangor Daily News, “A store man-ager at the Shaw’s Supermarket on MainStreet confirmed that the eels were inthe store’s parking lot, and assumed theycame from the Penobscot River acrossthe street. Store employees swept theeels up and returned them to the riversafely.”
Surely this appearance was anencouraging sign of eel resilience, a char-acteristic that recently led the federalgovernment to decide not to place theAmerican eel on the Endangered SpeciesList. Citing stable, but depleted, popula-tions, the U.S. Fish and Wildlife Servicerecommended “continuing efforts tomaintain healthy habitats, monitor har-vest levels, and improve river passage formigrating eels.”
Thornton’s research will providemore information about eel migrationthrough dams and rivers. She will alsolook at how much time eels spend in thePenobscot estuary, by analyzing the ear-bones, or otoliths, of previously sampledeels. The salts in marine water leave a
44 MAINE BOATS, HOMES & HARBORS | March / April 2016 | Issue 139
THE SECRET LIFE OF EELSPh
oto
by C
ory
Gard
ner
Researchers from the University of Maine have been tagging eelssuch as this two-foot long one to learn more about their migration.
Reprinted with permission of MAINE BOATS, HOMES & HARBORS • DIGITAL edition @ www.maineboats.com 45
chemical signature in the bone, whichgrows in layers similar to tree rings.Some eels, rather than traveling to freshwaters, apparently remain in bays andestuaries their whole life.
Eels can take 20 or 30 years toreach maturity, and they only spawn
once. Every single eel, then, representsthousands of miles of open ocean trav-el and an ability to surmount obstaclesas they follow an ancient motivation toreturn whence they came, then sendforth in turn many millions more oftheir own. ✮
Catherine Schmitt is Communications Direc-
tor for the Maine Sea Grant College Program
at the University of Maine. She is the author of
The President’s Salmon: Restoring the King
of Fish and Its Home Waters, published in
2015 by Down East Books.
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This mature, or silver eel, was photographed in 25 Mile Stream, north of Benton, on a rainy fall night. The migration of adult eels back to the ocean in the fall is triggered by some combination of rain-swollen rivers, darkness, and cooling temperatures. New research suggests eels use magnetic signals,
among other things, to navigate through the open ocean back to the Sargasso Sea where they spawn and die.
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