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American eel remains one of nature’s mysteries 5-22-15

American eel remains one of nature's mysteries

Martha's Vineyard Times
by Nelson Sigelman - May 20, 2015

A journey that began thousands of miles away from Martha's Vineyard continued with a struggle just beyond an Island roadway.

One week ago Monday, I joined a small group on the bank of Mill Brook, just below the aging Mill Pond dam, to assess the strenuous efforts of Johnny Hoy, West Tisbury herring warden, to fine-tune a fish ladder placed to provide a passage for herring over the concrete barrier that impedes an annual migration that predates the 17th century arrival of the first Mayhews.

Weeks earlier, herring in the hundreds had gathered in the pools below the dam, but hesitated to continue a journey that began in the Atlantic Ocean, then through the manmade cut in the barrier beach that separates Tisbury Great Pond from the sea, and on to the upper reaches of the pond in search of their natal waters.

Herring below the Mill Pond spillway, either unable or unwilling to use the fish ladder. Photo by Johnny Hoy.
Herring below the Mill Pond spillway, either unable or unwilling to use the fish ladder. Photo by Johnny Hoy.
John had tinkered with the boards that controlled flow, and used his considerable stonemasonry skills to create pools below the dam where migrating fish could stage. When he thought the fish were not honing in on the ladder outflow, he constructed a rock weir to direct fish to the opening of the fish ladder.

"It doesn't look bad. I don't know why this isn't passing fish," said Brad Chase, a Division of Marine Fisheries (DMF) senior marine fisheries biologist and diadromous fish expert. Brad and Ed Clarke, head of the DMF fishway crew, had arrived with materials, expecting to have to adjust the run, but after a close examination, they decided there was little they could improve upon.

"I think what you did is what needed to be done," Brad said. Still, the question remained, Why were the herring not using the run? Were they traveling at night? John could not say for sure.

Strong water flow, thought to be an issue, was discounted. John had watched what happened when after 40 years, the boards used to dam the Tiasquam and create a pond on the former Rainbow Farm were removed, with the support and permission of Grey Barn Farm owners Eric and Molly Glasgow. Herring had returned.

"I didn't think they were as powerful as I now know they are," John said, after watching the fish battle the pond outflow. "They just want to go up; they just want to keep going till they can't go any further."

Brad stepped into the pool below the Mill Pond dam for a closer look. He stooped and took a handful of gravel. When he opened his hand, a small natural miracle — an elver, or glass eel — wriggled in his palm.

Division of Marine Fisheries senior biologist Brad Chase holds a glass eel in the palm of his hand.
Division of Marine Fisheries senior biologist Brad Chase holds a glass eel in the palm of his hand.
The American eel is one of those species which remind us that natural mysteries remain in life. It is the only fish in North America that spawns in the ocean and grows to maturity in freshwater, a cycle we do not know a lot about. The juvenile eel Brad held in his hand was born in the Sargasso Sea.

"It is one of the most amazing migrations for fish that I know of in North America," Brad told me in a followup conversation to his morning visit. "Two thousand kilometers from the Sargasso Sea, heading westward toward the continent, and they end up almost anyplace from Brazil on up to Labrador. We just don't know where they are going to end up."

The eel that Brad picked up had traveled through Tisbury Great Pond in search of suitable habitat. If it survived, it could grow to more than one foot long before it returned to its birthplace in the Sargasso Sea.

Eels face many risks, not the least of which come from humans. The American eel is being considered for listing as an endangered species. Limited trap fishing is still allowed for adult eels. "Our commercial landings are at historic lows," Brad said. "They're absolutely the lowest that we've seen."

To add insult to injury, after cleaning out the European stocks, Asian buyers turned their attention to the U.S. Elvers are in high demand in the Asian market, where one pound commanded prices as high as $2,000 in 2012, according to DMF. Only South Carolina and Maine allow the limited harvesting of glass eels. With prices high, poachers are a continuing threat to any efforts to help restore eel populations. One poacher with a fine mesh net can set back a whole generation.

The eel Brad held had survived natural predators and poachers, and now was up against a dam. On the other side of the road, I dropped down to the dam and saw a remarkable sight. An elver struggled to snake its way up a moss-covered stretch of concrete, something they can do if the surface is wet and rough, Brad said. Ideally, Brad said, with no obstructions, the eel would follow Mill Brook up and feed until it reaches maturity.

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