The Pacific Lamprey – Salmon’s Excellent Friend by Dave Vedder

Few finny denizens of Northwest waters are less understood or more misunderstood than the salmon’s friend the Pacific Lamprey.

“Wait a minute” many of you are saying. Aren’t lampreys, eels that suck the blood out of our salmon and steelhead, and endanger swimmers? The answer is no, no, and no.

First off, the lamprey is NOT an eel.

As this photo illustrates many river dwellers feast on adult lamprey. Here a bald eagle tries to wrest a lamprey from a sea lion

Secondly, they do use salmon and many other creatures as a food source during one part of their life cycle, but they help the salmon in several ways you will learn if you read a bit farther, and lastly, while they are fierce-looking, I can find no record of a lamprey every attacking a human in the wild.

So let’s learn a bit about this misunderstood critter that once inhabited almost every creek, stream and river in the Northwest and even today keeps a toehold in many river systems.

The Pacific lamprey begins its life cycle when an adult female deposits as many as 230,000 eggs, typically in midsummer. Many of these eggs overflow the nest and become food for trout, salmon smolts, and other river dwellers.

The larvae sink into silty river beds and soft banks where they feed on microscopic nutrients for as long as six years. No doubt many Northwest anglers have unknowingly tramped over silty areas holding lamprey larvae.

Those who have actually seen the immature Lamprey typically assume they are salamanders, eels, ditch eels, or some alien river form.

And while we are at it, let’s clear up the misnomer almost all of us use. These guys are NOT eels. I repeat they are not eels. They are, in fact, a fish, in the family tridentata.

After three to six years the Lamprey larvae go through a simply amazing metamorphosis.

The scientific folks I interviewed have several multisyllabic terms for this change, but it is just flat amazing. The sightless, worm-like critter that has been hidden under the riverbed transforms itself into as something else altogether.

The sightless lamprey larvae drift downriver, where they can be an important food source for salmonids, birds, and other predators. As they move downriver, typically in the spring, they develop fins, eyes, teeth, and the distinctive sucker mouth we all associate with an adult lamprey.

By fall they are ready to enter the ocean where they spend 20 to 40 months looking for hosts that unwillingly provide them with nutrients that allow the lamprey to grow rapidly.

The adult lamprey is an opportunist and will attach itself to almost any fish or mammal they can find.

While they are, in fact, parasites, they typically do not kill their host. In most cases they drop off the host after a few hours. Normally, the lamprey does no harm to its host.

After their journey in the ocean, adult lamprey, typically weighing one to three pounds and approximately 24 inches long, return to their natal stream. This journey is not without its dangers. Because lampreys are extraordinarily high in fat (lamprey have a body fat content roughly twice that of a spring Chinook!), every predator in or near the river is looking for them.

When lampreys are abundant they constitute a significant portion of seal and sea lion diets. Of course, that is a huge plus for salmon migrating past the marine mammals. Eagles also relish the lamprey as the run timing often coincides with the baby eaglets' need for protein.

If the lamprey is fortunate enough to make it past the predators, dams, dewatered stream and polluted water, they mate, deposit their eggs and perish within a few weeks. But once again the lamprey provided the salmon an unintended benefit by providing food to smolts and resident trout as well as bringing ocean nutrients to the river systems.

(Studies have shown that a significant portion of nutrients needed by trees and insects is transported from the oceans by anadramous fish.)

Dead adult lampreys are a prime source of protein for many river dwellers, but perhaps more so the sturgeon than most. Several studies have documented sturgeon gorging of lamprey carcasses.

Today the Pacific lamprey is nowhere near its previous abundance.

But when the runs were strong native tribes harvested them in large numbers. The oily lamprey made an ideal food source that sustained them for months each year. Today, some first nation’s people still harvest small numbers of lamprey where the stocks are strong enough to allow limited harvest.

The Pacific Lamprey once ranged from Japan, the U.S. coast from Alaska to California, and well into Mexico. Sadly, their range is decreasing as are their overall numbers. Much like the Pacific salmon runs are declining at an alarming rate. All the usual suspects play a roll. Dams have significantly harmed lamprey populations, as have extreme weather events, pollution, dewatering areas where the larvae live, and very likely other factors not fully understood.

We know that Pacific Lampreys are in trouble.

In many systems, they are nonexistent above man-made obstructions. In those rivers where they do have a toehold, that hold is tenuous. For example, a study in 1966 found 46,758 lampreys in the Umpqua River; and only 34 in 2001. Similarly, the Snake River was estimated to hold 49,454 lamprey in 1963 and only 203 in 2001.

While the outlook for Pacific lamprey is dismal there are many dedicated biologists in a number of organizations, including The U.S. Fish and Wildlife Service, tribes and, several state agencies working hard to turn things around. This article came about because I met Ann Grote of the U.S. Fish and Wildlife Service while she and several biologists from the Yakima Nation were planting adult lampreys in the lower Wenatchee River.

Curious as to what they were up to, I struck up a conversation and soon became fascinated with the Pacific lamprey and the efforts to improve their numbers. Ann told me there are many obstacles to recovery including poor passage systems at dams, loss of prey in the ocean, including salmon, dewatered streams, pollution, diversions, and poorly designed culverts.

She said they are currently working on inexpensive modifications to fish ladders to improve access for lampreys. Chelan County PUD recently made modifications to the fish ladders at Rocky Reach Dam including installing ramps up the ladder to help the weak swimming lamprey make the passage. They also closed small discharge vents to keep the lamprey from getting swept back down the ladder. In tests conducted last year, dam operators found a 96% passage rate for lampreys, the best rate seen at any dam to date. 

If you are fortunate enough to see either adult lampreys or the worm-like larvae, please do not bother them and for goodness sake please do not even consider using the larvae for bait. They are important if an unsuspecting ally of our salmon trout and steelhead.

As in so many cases in nature, all systems need to be working for any to work well.

If you want to see live adult lampreys check out the Bonneville dam fish counting windows at night in midsummer.

-written by Dave Vedder