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Apr 10, 2018 11:34 AMPublication: The East Hampton Press & The Southampton Press

Eel Mysteries

This eel still has the yellow-brown colors of the species' immature phase. MIKE BOTTINI
Apr 10, 2018 11:52 AM

Geraldine Merida reported finding a large number of dead eels at the south end of Ligonee Brook on April 3. A closer inspection, and several photographs she sent, revealed that the eels’ heads were missing on quite a few.Ligonee is a mile-long narrow, shallow, ditched brook linking Long Pond, a freshwater body, with Sag Cove, part of the Peconic Estuary system. Its lower reaches, from at least the Bridgehampton Turnpike to the cove, is tidal, while its upper reaches rely on high groundwater levels to send water spilling out of the north end of Long Pond and down the creek. As such, it has provided a conduit, tenuous in some years and absent in others, for diadromous fish, those that spend part of their life cycle in freshwater and part in the sea.

The two prominent diadromous species utilizing the creek are the American eel and the alewife, and while they share the ecological distinction of migrating between salt and fresh waters, their implementation is quite different. Right now, and continuing throughout the spring, both migrate up tidal creeks to freshwater reaches. Alewives do this as mature adults to spawn, a strategy labeled anadromous or “upward-running.” The resulting young head back to sea in late summer and fall where they spend at least three years before maturing and joining the spawning run. Unlike eels, the adults do not perish after spawning but survive to spawn several years during their lifespan, less than 10 years.

The American eels migrating along with the alewives right now are juveniles in the form of several inch-long, whip-like elvers. These fragile-looking but amazingly resilient creatures have already journeyed a thousand miles from where they hatched a year ago in the Sargasso Sea. Under the cover of darkness, some will work their way up the tidal creeks toward their freshwater sources, scaling vertical dams and other obstacles en route. Others may decide to forgo the journey to freshwater and instead opt to take up residence in a stretch of brackish water within the estuary. Both will remain in their new haunts for five to as many as 40 years before undertaking the long, “downward-running” or catadromous trip to their ocean spawning grounds where they will mate and perish.

Geradine’s April 3, 2018, report reminded me of similar events documented at this location on April 16, 2014, by Callie Velmachos and on April 9, 2015, by Liz Joyce. Although neither of the latter reports included headless eels, nor as many as Geraldine tallied, all shared one unusual aspect: time of year.

The eels’ last journey begins in early fall and concludes in the Sargasso Sea in January. That begs the question: what were all these eels doing in upper portion of Ligonee Brook in April?

I wondered if they may have been unable to leave last fall because of low water levels, forcing them to overwinter at Long Pond and make a late departure. During the migration, eels undergo an amazing transformation. As NOAA fisheries biologist Vic Vecchio explained to me, “the silvering process changes the gross morphology of the American eel. That is, their eyes become much larger, their skin color changes, fins become dark or black, and they completely resorb their digestive system, turning all their energies into spawning. They essentially become a sack of gametes with just enough energy to make it to spawning, after which they die.”

Could their delayed start have depleted their energy stores, causing them to perish at the very start of their journey?

Vic added, “it is unlikely you are finding true “silver” eels here, especially in spring. My guess is that these individuals perished and began to lose their pigment leaving behind the pale or silvery color you are seeing. I’m not certain what to say about the dead eels. I know they are really hearty species, and it takes a lot to kill them. This is why they are a sentinel species for analysis of contaminants in surface waters.”

Vic suggests that we monitor this area and, should another episode occur, collect fresh specimens for examination by a wildlife pathologist.

As to the headless eels, it is not unusual to find predators keying in on consuming the highly nutritious brains when prey are very abundant and concentrated. This has been documented during salmon spawning runs out west, and in that case the headless fish carcasses are the work of bears. Every spring the North Sea alewife dreen is littered with headless alewives. The likely culprit in that case, as with the eels, is procyon lotor. Among the eel carcasses resting on the banks of Ligonee Brook were patches of snow, and imprinted in the snow were the telltale marks of the masked bandit: five-toes resembling a small human hand.

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