The thrashing black and amber fish in Stephen Coghlan’s grip is unsightly, but its humble appearance — a snake-like body, milky eyes and parasitic funnel of yellow teeth -— belie the sea lamprey’s importance to the small Sedgeunkedunk Stream and, possibly, Coghlan contends, some of the state’s most majestic rivers.
Coghlan, an associate professor of freshwater fisheries ecology at the University of Maine, has spent many hours ankle-deep in the Sedgeunkedunk (pronounced Sej-E-unk-e-dunk) studying the lamprey’s impact on the stream since the removal of two dams about three years ago allowed the fish to return to their traditional spawning grounds. In that time he has seen steady increases in the number of lamprey building nests on the stream bottom and, in the process, changing the environment, possibly making it more hospitable to highly prized sea-run fish, including Atlantic salmon.
“We’re trying to tell a story, and each year we get a little bit more information,” Coghlan says, carefully placing the now-weary lamprey into a submerged basket and jotting down the measurements of others caught and tagged that morning by his student researchers.
The story is set in the living laboratory of the Sedgeunkedunk Stream, a small tributary running north about 3.7 miles from Orrington, Maine, and into the Penobscot River in South Brewer.
On this sunny morning, Coghlan and his team of undergraduate and graduate students are on their daily “lamprey safari,” walking the stream and carefully hand-catching and tagging any lamprey they see. Each captured fish receives both a visible tag and an electronic tag that can be scanned for identification.
Part of the reason the lamprey are so easy to catch is that they’re very busy building their nests. And there’s some heavy lifting involved, too, as they use their sucker-like mouths and thrashing bodies to move rocks — some as big as grapefruits — into a mound where they will lay their eggs. An oval pit, worn clean and smooth by the lamprey’s slow, constant wriggling, is at the base of the mound.
Once sea lamprey spawn, they die. That’s it. But they leave behind three important things: their bottom-changing nests, their nutrient-rich carcasses and the next generation of lamprey.
Since the removal of the dams in 2008 and 2009, Coghlan and his team have documented increasing numbers of sea lamprey returning to the Sedgeunkedunk to build or enlarge their nests, which, in some cases, can be several feet across. Five years ago, there were about 60 fish. This year, he and his team tagged a record 250, and the fish are moving farther and farther upstream to spawn, expanding their range.