How Do These Hideous Blood-Sucking Parasites Fit Into the Ecology of Pacific Salmon?
Because of their distinctly elongated, tubular, disturbingly “snake-like” features, lamprey are often identified and referred to as eels. Although reactions to these creatures vary—anywhere from mild disgust to stomach-churning revulsion—according to one’s sensitivity to rather squirmy looking life forms, the following ditty by Ogden Nash seems particularly apropos:
I don’t mind eels
Except as meals.
And the way they feels.
Clearly, upon first glance, lamprey and eels are strikingly similar in appearance.
But, as the old maxim goes, appearances can be deceiving. In fact, the Pacific lamprey (Entosphenus tridentatus) is not an eel at all. It’s an entirely different species, belonging to the ancient lineage of fishes classified under the order Petromyzontiformes.
Eels, by contrast, are Anguilliformes, a slightly more modern, divergent order of fish related to tarpon and bonefish.
Despite the superficial similarities, eels are distinguished from lamprey by two traits: jaws and fins. Though not as pronounced as in other fishes, eels possess paired fins—a dorsal and anal fin that’s fused with the caudal (tail) fin in a single ribbon-like appendage running most of the length of its body. Eels also have hinged jaws, which in some species, such as Moray and wolf eels, are equipped with formidable, indeed scary, rows of wickedly sharp teeth.
While the lamprey does have fins located on the upper (dorsal) rear of its body, they are so slight and rudimentary as to appear vestigial, though perhaps providing some small aid in navigation. Speaking of which, lamprey are less than impressive swimmers, managing to negotiate rivers by creeping along the bottom in the slower current channels and clinging to rocks with their sucker-like mouths, thus accounting for the origin of its name.
The term lamprey is derived from the Latin conjunction lamptera, which translates to “stone licker” (lambere, to lick, + petra, stone).
Adult lampreys have large eyes, one nostril on top of the head (strange or what?), seven gill pores (smallish slits) on each side of the head, no scales, a cartilaginous skeleton and, yes, a Hooverish suction-nozzle mouth with concentric rings of back-curving teeth. When viewed up close or magnified, staring into the sucker-toothed maw of a Pacific lamprey is not unlike submitting to the big screen version of one of Hollywood’s most malevolent scifi aliens.
Vampires of the Deep
Pacific lamprey live in the ocean for a period ranging from about six months to over three years. During its adult stage in the marine environment the Pacific lamprey begins its parasitic phase, feeding upon the blood and bodily fluids of whatever species it can manage to clamp onto, including salmon, halibut, flatfish, rockfish, pollack and even whales (incidentally, lamprey do not kill their host).
Exactly how such a pathetically slow swimmer performs the feat of latching onto considerably swifter and more agile prey species remains a mystery. Ambush? Sneak attack? Mere proximity and glancing chance? What is known (having been caught in commercial haul nets) is that lamprey frequent depths from 300 to 2,600 feet, and as far out to sea as 60 miles or more. Upon reaching full size, typically 15 to 30 inches, and sufficient body composition—storage of fats and nutrients—
Pacific lampreys cease feeding and migrate back to freshwater, presumably to their natal streams. While living off reserves of fat tissue, lamprey gradually work their way upriver, reaching sexual maturity en-route, before finally completing the spawning cycle. Like salmon, lamprey are anadromous—born in freshwater, prospering as juveniles at sea, then returning as adults to freshwater to reproduce—and also like salmon, lamprey are semelparous—doomed to die after spawning.
Lamprey typically spawn in the same type of well-oxygenated, coldwater habitat favored by salmon and trout. Though far from pretty—defintely not the Brad and Angelina of the animal kingdom—the mating behavior of lamprey is downright romantic. The ritual begins with both the male and female carrying pebbles in their mouthes one at a time in order to construct the nest (redd). Upon completion of the nest the male wraps his body around the female and expresses the eggs, up to 100,000 of them, from her abdomen. He then unclenches and free fertilizes the eggs, after which they both fade and die. The embryos hatch at approximately 19 days and the blind larva, called ammocoetes (Greek for “sand dweller”), drift downstream to areas of slow current and fine silt deposits, a k a muck, where they burrow or bury themselves in a U-shaped form, with mouths near the surface. From their hideouts in the muck, the larvae filter-feed on a banquet of algae, diatoms and detritus. As they age and grow over a period of three to seven years, the larvae change locations to progressively deeper water and coarser matrixes of sand. Upon reaching the eyed-juvenile stage—now officially earning the title “lamprey”—they forsake the sedentary, buried-in-mud lifestyle and enter the water column, thereby harnessing the current for migrating out to the big blue Pacific.
Once again, sharing traits with salmon, Pacific lamprey distribution patterns roughly approximate those of other anadromous species on the West Coast. While river lamprey, Kern brook lamprey and Western brook lamprey (a non-parasitic species) are found in specific pockets and stretches scattered along drainages in western North America between the Sacramento River basin and SE Alaska, Pacific lamprey are widely distributed along the entire Pacific Rim. They have been found in an arc of locations from Baja, Mexico to major drainages in California, Oregon and Washington, and from there to the Alaskan Peninsula, and continuing on around to Japan and Korea.
Unfortunately, while the distribution of Pacific lamprey is wide and far ranging, their population numbers have become distressingly shallow.
Once so many lamprey jammed the pool below Willamette Falls—hundreds of thousands, weighing in the tons—that their abundance easily supported a commercial fishery. Now there are few. In the 1960s counts at Bonneville Dam pushed 400,000; in recent years a few hundred would be considered a banner run on the lower Columbia. At Winchester Dam on the North Umpqua, the run count of Pacific lamprey dropped from almost 50,000 in the 60s to less than 50 today. And so it goes in most of the watersheds in the western U.S. and Canada.
Should this be a concern? After all, lamprey are the Addams Family of fishes:
They’re creepy and they’re kooky, mysterious and spooky
They’re all together ooky, they’re the Lamprey fam-i-ly.
Sinuous, slithery, slippery and slimy. Hey, there’s not much to recommend the appallingly ugly lamprey, at least not as far as surface appearance goes. But wait a minute, it turns out there is. Indeed, there’s much to vindicate the lowly lamprey.
To start with, consider the prey/predator dynamic. True, during the adult stage Pacific lamprey have the annoying habit of trying to suck the lifeblood out of salmon and other fish species. To turn the table, however, because they’re high on the menu for other marine predators, especially seals and sea lions, adult lamprey function as a buffer to reduce predation on salmon, both in the ocean and river environments.
Think about it: what would be easier to chase down and devour, a swift streamlined salmon or a sluggish beast shaped like an overstuffed kielbasa?
Similarly, lamprey are commonly found in the gullets of other predatory fish and birds, particularly gulls and terns, that might otherwise prey more heavily on young salmon, especially smolts. At the other end of the spectrum, colonies of lamprey larva—sometimes referred to as “earthworms of the river”—provide a high fat food source for juvenile salmon. And just as spawned-out, decaying salmon supply nutrient-loading to freshwater ecosystems, so does a spawning/dying lamprey ultimately enrich the stream of its origin.
Then there’s the human equation.
Although for most of the populous lampreys are an acquired taste, for the tribes of the Columbia River basin the Pacific lamprey has long held special cultural significance. Historically the tribes maintained large lamprey fisheries at the confluence of the Snake and Columbia rivers, at the mouth of the Walla Walla River and at the base of Willamette Falls. The tribes dried and roasted lamprey not only as a dietary staple, but for use in ceremonies and celebrations. Furthermore, they extracted the oils from lamprey (which are considerable, given their lipid content) for medicinal purposes and last, but not least, as a hair grooming product, the progenitor of Brylcreme.
In contemporary times, lamprey oil has been found to have a medical application as an anticoagulant. And in the field of biomedical research lampreys are used as a model organism due to their large reticulospinal axons. In fact, lamprey axons are of sufficient size to allow for the microinjection of substances for experimental manipulation and to investigate synaptic transmission. In other words, the lowliest, most primitive of animals—dating back in the fossil record 450 million years (250 million years before sturgeon) —may one day help us, supposedly the highest form of animal, fully understand the fundamental principles of motor control in vertebrates.
The Lamprey’s Lament
So, where have all the lamprey gone? Part of the answer can be summed up in one word: concrete. The rest of the answer is far more complicated, uncertain and perplexing.
Recent data indicate that Pacific lamprey populations have been drastically reduced in many, if not most, of the river drainages in the West. Basically, they no longer exist above dams (concrete) and other impassible barriers in the larger river systems throughout Washington, Oregon and California, including most tellingly in the upper Snake and Columbia rivers. Some might argue that many other factors are to blame. Well, yes, there are a host of other problems. But the circumstantial evidence overwhelmingly points to dams as the main culprit.
Artificial barriers impede both the upstream migration of adult lamprey and the downstream movement of ammocoetes (lamprey larva) and macropthalmia (eyed- juveniles). The sad fact is that fish ladders designed to pass salmonids do not effectively pass lampreys. Pacific lamprey are not equipped with the high energy locomotion necessary for negotiating the water velocities and sharp and/or steep angles inherent in most fish ladders. Furthermore, since lamprey travel deeper in the water column (no air bladders) than salmon, traditional spill gates often block their passage.
Fish and Wildlife agencies in Washington and Oregon, along with the Army Corps of Engineers and the Columbia River Inter-Tribal Fish Commission (CRITFC), have in recent years been experimenting with new dam passage structures called “lamp ramps.” The ramps are basically a network of steel chutes, resembling rain gutters, with just enough water volume and flow to allow the lampreys to pass through, while also providing flat surfaces for them to latch onto. Because (as already noted) lamprey have difficulty making it into the entrance of the fish ladder, biologists determined that placing boulder-like mounds in the concrete channels may provide enough current breaks for the lamprey to more easily navigate their way into the structure. However, according to Brian McIlraith, Pacific lamprey project leader at CRITFC, they’re still “working out the kinks in terms of getting the lamp ramps situated where the lamprey can consistently find them.”
Of course, as Corps fish biologist David Clugston pointed out, any changes to the existing fish ladders must be carefully monitored to make sure they don’t interfere with salmon passage. He further posited that because the two species are so intertwined and cross-share habitat, one will probably not flourish without the other. “We’re not going to get salmon recovery unless we get lamprey recovery,” Clugston said. “They’re a forgotten species, but these are really important animals.”
Naturally, given that lamprey share the same rivers with salmon, they also share the same list of threats. In addition to the biggie—dams—lamprey declines can be attributed to a host of issues, including: dewatering (irrigation, diversion, reservoir management, etc.); pollution and degraded water quality; dredging (channel maintenance and mining); predation by non-native species (bass, walleye, northern pike-minnow); and that ever-looming catchall, ocean conditions (resulting in less prey/more predators). The threats involving water levels, water quality and stream structure are especially critical to the survival of ammocoetes because they’re more or less stuck in place, unable to simply pack up and move away from areas that get dewatered, contaminated, or physically disturbed. All it takes is one dewatering event, particularly in the upper reaches of small streams or in a lagoon to wipe out an entire local population of lamprey. An egregious example of the impact of stream degradation occurred in the upper John Day River where it appears that extensive dredge-mining operations (beginning in the late 1800s) totally annihilated lamprey populations in the basin, from which there has been no recovery.
Ironically, while agencies are scrambling to save the Pacific lamprey in major watersheds in the West, notably the Columbia, back East in the Great Lakes sea lamprey (Petromyzon marinus), a parasitic species endemic to the Atlantic, have become a scourge. Having first entered the Great Lakes by means of artificial canals constructed during the early 20th century, the sea lamprey are now considered an invasive species in the lakes, and with no natural enemies to thin their ranks they’ve become a menace, preying upon fish of commercial value, such as salmon and lake trout. As complicated and expensive as it has become to eradicate the seemingly intractable sea lamprey, the corollary of that is the ongoing effort to preserve what’s left of Pacific lamprey populations. So in case there’s any confusion between the two species, think of it this way: sea lamprey—bad; Pacific lamprey—good.
One of the most imposing obstacles to mounting a recovery effort for Pacific lamprey is the woeful lack of information. From the mid-1960s through the ‘80s there was little or no biological monitoring of lamprey. No numbers, no data, no nothing. Consequently, there’s a critical data gap regarding population baselines, methods to assess distribution and abundance, population dynamics, and even the ascertainment of a complete biological and life history picture. In the words of Brian McIlraith, “We’re about 30 or 40 years behind on what we know about what’s going on with Pacific lamprey in the West and here in the Columbia River.”
Some biologists have warned that Pacific lamprey may be viewed as a bio-indicator—a not so pretty canary-in-the-coal-mine species, a creature whose immediate wellbeing may be used to monitor the condition of a particular ecosystem.
Hopefully, man will get his act together on the Columbia and on river systems elsewhere asap, because in a very real sense, a bio-indicator is just modern parlance for “omen”, a word that musters the same dark connotations today as it did during the medieval ages.
- written by Sean Connolly
Division of Fisheries Resources
U.S. Fish and Wildlife Service