Mysterious lamprey and the invisible project

By Cori Reed
District 1 Public Information Officer

Below U.S. Highway 101 in rural Northern California, the Cedar Creek Arch Culvert Repair will have a huge impact for the Pacific Lamprey’s ecosystem.

The Cedar Creek project is 200 feet below U.S. Highway 101, approximately two miles south of Leggett in Mendocino County. The Pilot Fish Passage Assessment Study ranks Cedar Creek as sixth in priority in District 1. Cedar Creek flows into the South Fork of the Eel River, and the existing design of the fish ladder, weirs (low dams), and plunge pool were all listed as a partial barrier to fish. This project was initiated to repair a 21-foot-high by 22-foot-wide 763-foot-long, cast-in-place, reinforced concrete arch culvert and upgrade fish passage capacity. The culvert was one of the largest structures to be buried under that much fill when built in 1969.

Pacific Lampreys are a scary looking prehistoric fish that fish biologist don’t know a lot about. They played a role in the naming of the Eel River. Explorer Josiah Gregg mistakenly gave the Eel River its name after Native Americans gave lamprey to his starving party of men at the river in 1850. They are an eel-like nocturnal fish and hide in the stream bottom for the first five to seven years. During this time they are filter feeders and help preserve the water quality for other species. Once they are adults their bodies radically change: they develop eyes, rearrange internal organs, and grow a toothed, sucking disk mouth. Lampreys head to the ocean and use their new sucker mouth to become parasitic on larger fish and marine mammals. They return to the rivers to spawn after 2-3 years in the ocean. This is where they run into trouble. Adult Lampreys are about 2 feet long and weak swimmers compared to other spawning fish. They can’t jump or use common fish ladders to help ease their migration upstream to their spawning grounds.

Kristine D. Pepper, P.E., hydraulics engineer with 17 years of experience at District 1, attended a presentation in 2013 on Pacific Lampreys by Damon Goodman, with the Arcata U.S. Fish and Wildlife Service office. She was designing the Cedar Creek project at the time and researched if the lamprey’s passage was also being restricted by the old design of the culvert. Pepper reached out to Goodman and discovered that, with some modifications, the new weirs could be adjusted to help the lamprey navigate them. She proposed the top of the weir be rounded with a large radius on one side to allow lamprey to use their suckers and bodies to help climb over, while the other side would be square for the salmonids. This the first time lamprey passage of this type has been included in a Caltrans project. “If this is successful, then Caltrans will include this in future projects. I am also excited to see just what the results are and how we can improve the design for next time” Pepper said.

The modification for the lamprey was unusual since they are not on the endangered species listing and biologists know little about them. The lamprey have declined in numbers in recent years. However, 2017 seems to be banner year for them possibly due to the extremely wet winter. Lots of time and money has been spent on research and building fish passages for Pacific salmon and other salmonids, but the little-known lamprey has slipped through the cracks. Lamprey are important to the Native American culture and tradition. They are a traditional food source, high in protein, and available when salmon are not.  The lamprey, also high in fat, are a good food source for bears, eagles, raccoons, and other wildlife. “Even though the lampreys are not endangered, I don’t want to inhibit the natural flow of any species in the river with our projects” said Pepper.

Construction of the $5.7 million project started in May 2017 and is expected to wrap up October 2018.

“This was not an easy project” said Pepper. “I enjoyed it because it was a challenge. That is what I like about engineering at Caltrans.”