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July 20, 2011
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From flesh-eating monster to ecosystem engineer

Redemption for the sea lamprey

by Dr. Heather Deese and Catherine Schmitt

Graduate student Rob Hogg holds a sea lamprey found in the recently restored Sedgeunkedunk Stream.
Graduate student Rob Hogg holds a sea lamprey found in the recently restored Sedgeunkedunk Stream. Photo: Stephen Coghlan

“Body elongate, eel-like. Jaws absent, mouth forming broad, elliptical hood armed with horny, hooked teeth arranged in 11 or 12 rows, innermost teeth largest.”

This is not a detail from some alien encounter, but the opening lines of Henry Bigelow’s description of the sea lamprey, Petromyzon marinus, an ancient fish with a lineage that extends back some 530 million years.

Like some other sea-run fish native to the Maine coast, lamprey have long suffered from a bad reputation, mostly because of the damage the species has caused in some of the Great Lakes.

Yes, adult lamprey do eat other fish in the ocean, including salmon, cod, haddock, swordfish and bluefin tuna. “They fasten on to the side of their victim, where they rasp away until they tear through the skin or scales and are able to suck the blood,” wrote Bigelow. But now, researchers are finding that when it comes inland to spawn in late spring, this primitive, resilient fish actually does some good in Maine rivers, from cleaning out streambeds to playing architect for nesting Atlantic salmon.

Dr. Stephen Coghlan, an assistant professor of freshwater fisheries ecology at the University of Maine, and his graduate student Robert Hogg have been getting to know this creature with its small, dark eyes and slimy skin mottled black brown and greenish gray. A fish without scales or jaws, the strong, fast swimming lamprey has found a home in Sedgeunkedunk Stream, a tributary of the Penobscot River in Orrington and Brewer, Maine.

“To our knowledge, our study is the first to quantify effects of spawning sea lamprey on stream habitat in the context of Atlantic salmon restoration,” said Coghlan, whose lamprey research is funded by Maine Sea Grant. Like salmon, lamprey require fast-moving water and a gravelly stream bottom for spawning. As they prepare to mate and lay eggs, sea lamprey spend hours building nests. Working together, males and females use their mouths to pick up stones as big as a man’s fist and drag them into a pile, excavating pits, building mounds, loosening silt and mud from the stream bottom and improving water flows. The male and female will mate upstream, and the spawn will drift into the nest, settling in the cracks between rocks. They don’t feed when they migrate inland to reproduce, and apparently they don’t return to the stream where they hatched, but follow the scent of larval lamprey to find good spawning habitat. The adults die within days of spawning; larvae leave the nest within a week and burrow downstream. It could be months or years before they emerge, transformed, into juvenile lampreys and head for the sea.

Coghlan is also looking at how decomposing lamprey carcasses affect nutrients in the stream. When they come from the ocean, sea-run fish like alewives, salmon, and lamprey bring with them large quantities of ocean nutrients and energy. They enter freshwater streams, rivers and lakes, areas that regularly lose nutrients through normal processes of rainfall, runoff, and river discharge. In the past, the millions of fish that moved from the Gulf of Maine into inland watersheds to spawn helped to fertilize the landscape. And, of course, these fish were food for people. The thousands of dams erected throughout Maine in the last 250 years severed these links, preventing sea-run fish from providing valuable services and eliminating a local source of food.

Despite current momentum for restoring connections between rivers and the sea, fewer than five percent of all dam removals in the U.S. are coupled with rigorous biological monitoring procedures. The lamprey study is part of a recent restoration project on Sedgeunkedunk Stream that is serving as a case study for scientists interested in documenting how quickly fish populations and stream food webs respond to barrier removal.

Since 2009, when one dam was bypassed with a rock-ramp fishway and another dam was removed entirely, sea-run or anadromous fishes have regained access to six kilometers of Sedgeunkedunk Stream and 1,300 acres of upstream pond habitat. Coghlan began studying the stream before the dam removals to collect baseline data. A nearby stream outside of the restoration is serving as a reference site.

In summer 2010, after removal of the Mill Dam, salmon quickly moved upstream, and lamprey and alewife swam past the old dam site the following spring, almost as if they had been waiting. Prior to dam removal, Coghlan and his co-investigators estimated that 47 sea lamprey constructed 31 nests along 700 meters of habitat in the lowermost portion of Sedgeunkedunk Stream. In 2010 after dam removal, they estimated that 150 sea lamprey constructed 130 nests along five kilometers of stream.

Come summer, Atlantic salmon and brook trout will move into the stream where the lampreys have done their architectural work. “We don’t know for sure that salmon use old lamprey nests for their own spawning, but it’s likely,” said Coghlan, “and if they do, we’re not sure if they seek out abandoned nests actively, or those old nests happen to be in the right habitat.”

It appears that, in their reclamation of Sedgeunkedunk Stream, the sea lamprey have also begun to redeem their image as valuable participants in the dynamic food web of Maine’s coastal waters.

This article is made possible in part by funds from Maine Sea Grant.

Heather Deese holds a doctorate in oceanography and is the Island Institute’s senior programs director – marine initiatives. Catherine Schmitt is communications coordinator for Maine Sea Grant.

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