Lamprey legacy: Eel-like fish return after dam removal

The Pacific lamprey, a native eel-like fish wiped out by construction of the Elwha dams, is making an extraordinary comeback today, adding to species diversity in the river and increasing the food supply for other aquatic creatures.

Lamprey as a species have been largely ignored, even despised at times, while major ecosystem-restoration projects throughout the Northwest have focused on the needs of salmon. The black, slimy appearance of lamprey along with their parasitic nature do not help them forge a large fanbase, yet in recent years fisheries biologists have come to recognize the ecological importance of this ancient fish species.

“What I love about lamprey is that they are one of the oldest fish on Earth, and they are virtually unchanged from 360 million years ago,” said Rebecca Paradis Mahan, who studied lamprey as a biologist for the Lower Elwha Klallam Tribe. “They have persisted through time and massive habitat loss, and they are the rock stars of recolonization.”

Lamprey are important culturally to Native Americans, especially in the Columbia River system where tribes traditionally catch and eat them, as they have for centuries. As dams were built, they greatly inhibited lamprey migration and nearly drove the species to extinction.

By all accounts, Pacific lamprey, Entosphenus tridentatus, were abundant in the Elwha River before the dams were built, and they are still hanging on in most rivers on the Olympic Peninsula, said Mahan, who took a job last June as Clallam County’s habitat biologist. After dam removal, lamprey quickly moved upstream in the Elwha, where a growing number flourished in Indian Creek — above the lower Elwha Dam site — and a few migrated all the way upstream to Boulder Creek — beyond the upper Glines Canyon Dam site, she said.

“They were first seen in Indian Creek, where we saw spawned out adults in 2014,” she said. “That tells us that they went right up and into the creek.”

Typically, lamprey leave the saltwater and head into freshwater starting in the spring as they prepare to spawn. Swimming upstream, they eventually find a place to hide out, often under a rock, where they will wait until the following spring to find a mate. During this time, they live off their stored fat without eating. After spawning in the riverbed, adult lamprey soon die.

After about two weeks, larval lamprey, known as ammocoetes, hatch from the eggs and drift downstream until they come to silty sediment in which to burrow. The larvae are filter-feeders, consuming organic debris, algae and bacteria. They may live as ammocoetes for up to seven years and grow to about 6 inches before undergoing a dramatic physical restructuring, transforming from eyeless, wormlike filter-feeders to active, eyed predators. This juvenile stage then heads downstream to saltwater. They attach to fish, including salmon, flatfish, rockfish and hake, and occasionally marine mammals. The attachment does not seem to seriously injure most hosts, although they may display a scar on the skin where the lamprey hooked on with its mouth.

All three lamprey life forms can provide a good food source for fish, birds and mammals, with relative size a factor. When fat-rich lamprey are plentiful, they may serve as “buffers” for salmon and steelhead, meaning that predators may turn their attention to the more abundant lamprey while reducing predation on salmonids.

Lamprey are important culturally to Native Americans, especially in the Columbia River system where tribes traditionally catch and eat them, as they have for centuries. As dams were built, they greatly inhibited lamprey migration and nearly drove the species to extinction. Today, ambitious restoration projects involve moving adult Pacific lamprey upstream past the dams on the Columbia.

Adult lamprey are known to climb up steep waterfalls by attaching to rocks with their suction-cup mouths and inching their way along. What causes them problems are concrete culverts and fish ladders, especially those with sharp edges. Lamprey have no way of navigating around a 90-degree corner, so they are often stopped by structures built for salmon passage.

The Elwha Dam was erected without a fish ladder, and the lamprey had no chance of survival above the dam. The Lower Elwha Klallam Tribe mourned the loss of the lamprey, most often used as bait fish to catch a wide variety of available fish, said Mahan, who has interviewed tribal elders. Occasionally, an adult lamprey would come into the river below the dam, but habitat was sparce for the critical larval stage of life.

Genetically, lamprey are more alike than different throughout their range along the West Coast. One reason is that the adult lamprey often hitch a ride on fish that travel great distances. When lamprey drop off to spawn, they may be far from where they started, thus mixing their genes in distant places.

With samples from lamprey coming out of Indian Creek as well as samples from migrants leaving the river, the researchers were able to report a 12-fold increase in population within three years of dam removal.

Unlike salmon, which want to return home, lamprey tend to seek out any good place to spawn. Salmon use their sense of smell to follow the unique chemical signature back to their home streams, whereas adult lamprey will key on the smell of pheromones produced by larval lamprey. As a result, lamprey spawners tend to head toward places where lamprey have been before.

This tendency to seek out larval lamprey might not produce the best outcome for the Elwha River, where suitable habitat for lamprey has been unoccupied for 100 years, Mahan said. Fortunately, it appears that lamprey wander around enough to find good habitat if given enough time.

“These fish will go into a system and just nose around — even where they don’t smell pheromones,” she said. “They’ve proven in the Elwha and in other watersheds that they can recolonize places where they weren’t before.”

Indian Creek has emerged as one of the best places in the Elwha to produce lamprey as well as coho salmon and certain other fish. Higher temperatures because of Lake Sutherland and the connection to extensive wetlands are likely factors, experts say. A year after the first adult lamprey moved into Indian Creek in 2012, young ammocoetes were observed. Annual counts of ammocoetes caught in a trap on Indian Creek grew from 132 in 2014 to 407 in 2015 and to 1,805 in 2016. By last year, the number had grown to 3,914.

Because the ammocoetes are known to stay in the stream for several years, researchers were surprised when a significant number of migrating juveniles were trapped starting in 2016 with 71 individuals, increasing to 600 in 2017 and rising to 675 this past year.

Advanced genetic techniques were used to reveal likely kinship among 773 individuals (larvae, juveniles and adults) captured in the Elwha River. The technique compares the genetic makeup of individuals by focusing on 263 segments of DNA used as markers (single-nucleotide polymorphisms). Analyzing the data with computers connects the dots to reveal characteristics of the population — such as number of lamprey likely to have the same parents, according to Jon Hess, senior fisheries geneticist for the Columbia Inter-Tribal Fish Commission who has been studying lamprey genetics for the past 10 years.

“This process gives you an idea about how many spawners there were, based on how many individuals could be considered siblings,” Hess said. “One of the things we wanted to know was how the production was distributed, what proportions were coming from different streams.”

With samples from lamprey coming out of Indian Creek as well as samples from migrants leaving the river, the researchers were able to report a 12-fold increase in population within three years of dam removal. They also found that 41 percent of the production to that point was coming from Indian Creek. The study was published in 2020 in the journal Transactions of the American Fisheries Society.

Some 40 lamprey were moved into the Elwha from other rivers, yet the genetics analysis showed that all or nearly all of the lamprey in the river were the result of colonization, not production from those transplants. Those findings support the strategy of natural recolonization over time rather than transplanting more lamprey from other areas.

Although similar genetic makeup is seen for all Pacific lamprey along the West Coast, extensive studies have been able to tease out subtle differences on a regional scale — presumably because of the greater likelihood that lamprey will be closer to their stream of origin than far away, Hess said. Based on this ongoing analysis, lamprey recolonizing the Elwha are associated with a group that includes Puget Sound, Vancouver Island and the Lower Columbia River, as opposed to groups farther north in Canada, farther south in Oregon and California or farther to the interior of the continent.

Despite a high rate of gene exchange among lamprey and only slight regional differences, Hess and a wide-ranging group of collaborators have discovered a gene that strongly influences body size, often described by measuring overall length. Lamprey that must swim far upstream, such as those in the Columbia River, tend to have a gene variant that makes them relatively long. Those in more coastal areas tend to have a variant that makes them relatively short.

Presumably, the larger body size gives the long-distance migrants an advantage by having more stored fat to use for energy, Hess said. Based on studies in the Willamette River of Oregon, an individual lamprey that inherits a “long gene” from one parent and a “short gene” from the other parent tends to travel an intermediate distance when compared to those with two “long genes” and those with two “short genes.”

So far, most lamprey in the Elwha, like other coastal lamprey, have been found with two “short genes.” It appears that the shorter Elwha lamprey are making it safely upstream without the extra fat stores found in their cousins from the upper Columbia River.