Slippery Customer

Throughout the Middle Ages and even in our modern times, there has been a veritable frenzy to find a male eel.

—Sigmund Freud, Letters to Eduard Silberstein

Aristotle’s mystery would go unsolved for at least two millennia. Nobody in all that time could divine how eels reproduced, nor even whether there were distinct males and females. Finally, in the year 1707, a suspiciously plump female eel sold in the Italian port of Comacchio was found to be swollen with eggs. Eels, it would appear, did indeed have gender. But where were the males? This new puzzle would vex scientists for 200 more years, until the arrival of another towering intellect. Sigmund Freud, just nineteen years old and newly enrolled in the University of Vienna, was dispatched to Italy in 1876 to search for eel testes. One year earlier, a Polish zoologist named Syrski had written of mysterious “lobed organs” in larger eels netted near Trieste (some over 12 feet in length!) that he suspected were the long-lost gonads.² Young Sigmund was given more than 400 specimens to dissect and examine under a microscope, which he described in meticulous detail. He was stymied, however, by the simple fact that he did not know exactly what he was looking for. After weeks rummaging for testes, he was becoming testy himself. “Recently, a zoologist in Trieste claimed to have found testicles and thus to have discovered the male eel,” Sigmund groused in a letter to a classmate, “but since he apparently didn’t know what a microscope is, he failed to provide an exact description of them.”³ In the end, however, he convinced himself that he had indeed identified the elusive testes, using a bit of logical double-negativity that would have done Aristotle proud. “The microscopic examination of the lobe organ does not contradict the view that the lobe organ is the testicle of the eel,” he wrote in his very first scientific publication.⁴

Freud seemed to know instinctively why his eel examinations were inconclusive. “I found the most advanced state of the lobe organ only in the larger eels, from about 400 to 430 cm, more frequently in September and the following months than in March. During the whole period of my investigations, however, I came across forms of the lobe organ in smaller eels which I must regard as underdeveloped.”⁵ Demonstrating an impressive grasp of the eel life cycle, having only handled immature specimens, Sigmund hypothesized that the testes were not yet fully formed because “the eels are not in the least prepared for the reproduction business when they go out into the sea.” Freud made his way back to Vienna, perhaps to prepare for the reproduction business himself, as he would soon propose to his wife Martha. Twenty years after he left Italy, a mature male eel with fully formed testes was finally caught near Sicily, dispelling Aristotle’s mystery once and for all.⁶

There was one very good reason why the reproduction of eels had stumped Aristotle, Freud, and the long line of scientists that stretched between them. That reason is that eels mate very far from Europe. Eels belong to a select group of fishes that are diadromous, traveling between salt and fresh water to breed. Specifically, eels are catadromous, a crossword vowel bonanza describing fish who reproduce in salt water and later swim into freshwater streams and ponds where they spend the majority of their lives. European eels, triggered by a complex set of environmental and hormonal cues, swim downstream from their freshwater home until they reach the ocean, and only then begin to develop the sexual organs that Freud sought. Autumn marks the onset of the breeding season, explaining nicely why young Sigmund found more advanced organs in the largest (and oldest) eels caught in September.

Johannes Schmidt, a Danish biologist who started his career at the dawn of the twentieth century, was already aware that eels reproduce at sea. Less celebrated than the scientists who came before him, he would outwork both Aristotle and Freud to solve the last outstanding puzzle: where do eels mate? Having completed his doctoral research on mangroves, Schmidt stumbled across a single eel larva in the North Atlantic, a transparent ribbon just three inches long. Eels share the same larval form as tarpon and bonefish, a leptocephalus. From that serendipitous beginning in 1904, it would take him seventeen years, three research vessels, twenty-three sampling freighters, and the whole of World War I before he had his answer. He began finding smaller larvae the further southwest he traveled from Europe: first two inches off the coast of Africa, then just an inch and a quarter in the middle Atlantic, under an inch as he approached the Caribbean, then nearly microscopic. After capturing and examining more than 6000 leptocephali, and painstakingly documenting their locations, he had his map: the smallest larvae all came from an elliptical area now known as the Sargasso Sea. “Hosts of eels from the most distant corners of our continent,” he summarized with a certain flair, “shape their course south-west across the ocean, as their ancestors for unnumbered generations have done before them. How long the journey lasts we cannot say, but we know now the destination sought: a certain area situated in the western Atlantic, N.E. and N. of the West Indies. Here lie the breeding grounds of the eel.”⁷ The coda of this epic detective story was contributed by a young biologist working for the New York Zoological Society, appropriately named Marie Fish. In 1926 she discovered actual eggs of the American eel in samples collected from the Sargasso Sea, proof positive that the Western Atlantic was indeed the cradle of eel reproduction. Triumphantly, she laid to rest a scientific riddle that had persisted for 2300 years: “the sea has given up the last secret concerning the life history of the American eel which it has jealously guarded for so many centuries.”⁸

At the heart of these concentric mysteries are several species of freshwater eels, cousins to morays and their coral reef ilk, but residing primarily in freshwater lakes and rivers across the globe. Aristotle and Freud were bamboozled by the European eel (Anguilla anguilla), but in the Sargasso their eggs and larvae mix with those of American eels (A. rostrata). As the larvae develop, they enter the Gulf Stream and make their way north and east. American eels (distinguished only by their number of vertebrae and muscle segments) develop quickly, and after a single year are strong enough to fight the current, turn west, and hightail it for the coast of North America. Their European counterparts grow more slowly, requiring two to four years to attain the same degree of independence, and consequently are swept by east-flowing currents to the opposite side of the Atlantic. Amassing near their respective coasts, in their respective graduation years, great shoals of juvenile eels gather. By now they have transformed out of their ribbon-like leptocephalus form into slender versions of their adult selves. Still they are nearly transparent, earning them the moniker of “glass eels.” By the millions, glass eels wait for slack river flows and rising tides before plunging into river mouths and battling their way upstream, onto the continental land mass where they will spend their entire adult life. At least, that is, until the siren call of mating summons them back to the sea.

Of the remaining eighteen species of eels, some glide through Australian streams (short-finned eel, A. australis), slip amid ponds in Japan and China (Japanese eel, A. japonica), or meander the rivers of Southeast Asia (giant mottled eel, A. marmorata). Despite their far-flung distribution, most eels are quite similar in form and behavior. Highly elongated fishes, with long and supple backbones that permit them to swim with a distinctive side-winding motion (appropriately dubbed “anguilliform”), they can even swim backwards. Adult eels are draped with minute scales, so small they barely can be detected, but their bodies also are covered with a thick mucus that renders them slippery, slimy, and probably better protected against parasites. Forward-facing eyes and prominent nostrils allow them to see and smell prey, which they pursue voraciously. Along their muscular back a ribbon-like dorsal fin extends all the way down the body, wraps around the pointed tail tip, and joins with a similarly fringing anal fin, like a low fence that outlines two-thirds of their body. European eels have slightly underslung mouths giving them a faintly bemused appearance; their American cousins are distinguished by a more pointed snout (their scientific name rostrata means “beaked”). Most eels are a dark brownish-yellow as adults, though populations inhabiting clearer waters tend to be lighter in color. At this stage they are sometimes referred to as “yellow eels,” and they may live in their freshwater homes for thirty years or more. They are biding their time, waiting for a signal, and they are exceptionally patient. Captive eels have been known to survive fifty or even eighty years in aquariums. In Sweden, where it once was not uncommon to toss an eel into a freshly dug well so as to keep it free of insects and other non-potable creatures, one well-dweller is alleged to have survived for 150 years.⁹

While eels pass the time in ponds and rivers, they grow steadily from the glassy immature phase into large, brawny predators. Formidable hunters, they stalk prey by night, taking crustaceans, insects, and all manner of fishes, occasionally even surging from the water’s edge to seize an unwitting frog or baby bird. During the day, eels retire beneath stones or sediment. If a hard winter should strike, they survive by burrowing into the mud for a few months. Should their pond or stream dry up, they are capable of traveling significant distances overland, winding through wet herbs and grass, even climbing low walls and other obstacles by braiding themselves together into a pillar. If moved from its home, an adult eel will migrate many miles to return, showing tremendous navigation abilities. After several decades spent in upland waters, however, subtle signals prompt the eel to embark on a final, and massively ambitious migration. Rachel Carson, in many ways the poet laureate of conservation, dramatized how a female eel might sense these cues: “A strange restiveness was growing … For the first time in her adult life, the food hunger was forgotten. In its place was a strange, new hunger, formless and ill-defined. Its dimly perceived object was a place of warmth and darkness.”¹⁰ That strange new hunger is the song of the sea, summoning eels from Europe and America to enter the ocean and make their way to the balmy Sargasso Sea.

The magnitude of this transoceanic undertaking is staggering. An eel must navigate downstream and evade all manner of dams, sluices, dikes, mills, power plants, and other obstacles.¹¹ Its wall-climbing and grass-clambering skills become invaluable, even life saving. Along the way predators from bears to hawks and more seize the chance to dip a paw or talon into a stream positively boiling with tasty flesh. Should the eel survive its overland journey and reach the ocean, its migration will have barely begun. For this voyage, however, the eel’s old body no longer serves. Prompted by entry into salt water, its fins grow longer, for better propulsion. Eyes enlarge, and turn blue, the better to see in the open ocean. Its sense of olfaction sharpens, allowing the eel to smell its way toward the Sargasso.¹² The yellowish color is replaced by silver on the belly, and stripes on the flanks. Reproductive organs begin to develop; at the same time its stomach and intestines cease functioning and nearly disappear. From this moment on, the eel will eat no more, subsisting only on fat stores built up during years of freshwater hunting.¹³ In readiness for deep diving, the eel’s swim bladder prepares for frequent use: the gas gland ramps up its pumping ability, and guanine crystals are deposited in the bladder walls to decrease its gas permeability.¹⁴ Swim bladders in silver eels are five times as effective at generating and retaining gas as they were just a few weeks earlier, in their yellow-bodied selves. But its very entry into the ocean, where the eel is surrounded by salty water, represents the most fundamental challenge of all. The eel must adapt, and quickly, or risk dehydration and death.

All living organisms are composed mostly of water, and if immersed in an ocean, the salt inexorably draws out that internal moisture. This is why fish are cured (i.e., dried) with salt, and why you get thirsty after a swim in the sea. It is not, however, why your fingers get “pruney” when swimming, a reaction actually driven by the nervous system; as evidence, people with nerve damage to their hands never get wrinkled fingertips. Fishes who spend almost their entire lives in freshwater begin to dehydrate as soon as they enter the sea. In response eels drink seawater, and now a desalination battle begins. Proteins like prolactin and hormones like cortisol and angiotensin course through the body, initiating a wave of physiological changes to fight salt.¹⁵ When the first mouthful hits the esophagus, salts are absorbed so the water reaching the stomach is a third less salty.¹⁶ Next, the swallowed water passes into the intestine, where both water and salt are absorbed into the bloodstream by newly stimulated cells lining the gut. Those intestinal wall cells spend energy to actively pump salt out of the gut, and water is drawn along passively: the eel actually gains some internal water from the sea. But the blood is now higher in salt, and as it reaches the gills, that excess salt must be eliminated. Salt is actively driven across the delicate folds of the gills, shed back into the ocean while precious water is retained. Eel gills are six times more water-impermeable in the ocean than in a lake, a vital adaptation that blocks internal water from diffusing into the sea.¹⁷ Fish kidneys, unlike those of land animals, are not capable of making concentrated urine, so they are of little use in this transition; however, in a few pages they will help salmon survive entry into fresh water. Thanks to the sweeping changes from mouth to gills, eels are able to survive in their new briny environment within a matter of days. Now they are ready to venture across an ocean.

From the shores of Europe, a migrating female eel sets out toward the southwest, along with tens or hundreds of thousands of kinfolk, and follows the seaboard as far as the coast of Africa. There she turns to the right and hitches a ride on a powerful west-flowing current that carries her across the Atlantic. The round-about route is actually easier to swim, thanks to the current, than if she had set a straight course to the Sargasso Sea. Since migrating eels have ceased eating, she must power her peregrination entirely with stored energy, converting fat and protein into miles as she swims methodically toward the New World. Now her highly efficient side-winding style comes to the fore, as she has just embarked on a journey of some 3500 miles: anguilliform swimming burns only one-sixth the energy of a typical fish to cross the same number of miles.¹⁸ Still, upon arrival at the breeding grounds she must court a mate and lay eggs—from 2 million in smaller eels to 5 million in larger individuals—so energy saved by hitching a ride on a cross-Atlantic current will become invaluable.¹⁹

As she swims, she adopts an odd habit of changing depths. During the night she will swim at depths of around 500 feet, but by day she descends to 1500 or even 3000 feet. Predator avoidance may partly drive this yo-yo profile, but the leading hypothesis suggests thermoregulation is the cause. Swimming in deep, cold water (around 50 °F) may delay development of her reproductive organs, stalling their depletion of precious energy until absolutely necessary; ascending by night into warmer waters boosts her metabolism and swimming speed, giving her the best of both climates.²⁰ Along the journey, she will rely on her newly honed olfactory system, and an internal compass, to navigate. Eels can detect the intensity and bearing of Earth’s magnetic fields, allowing them to maintain a westerly course while crossing an ocean largely devoid of landmarks.²¹ Even with all these advantages, when this eel reaches the Sargasso she will have melted 40 percent of her fat stores to fuel the voyage;²² the remaining 60 percent will be mobilized to produce millions of eggs.²³ After six months or more at sea, this eel has reached the end of her journey and the culmination of her long story arc. Soon after releasing her eggs to float to the surface of the Sargasso, she will perish, her life’s work—and a round-trip crossing of the Atlantic Ocean—complete.

Most species of eels are semelparous: they reproduce just once in their lifetime, then they expire, making every baby eel an orphan. When the microscopic, leaf-like larvae hatch they drift into currents bearing them to Europe and North America. A young eel does not return to the stream where its parents lived, a homing instinct found in other fishes who migrate between fresh and salt waters, such as salmon. Across Europe the entire eel population is genetically similar, since parents from thousands of freshwater sources all mix together in the Sargasso, and their offspring upon returning select rivers nearly at random.²⁴ Still, for reasons not yet understood, some streams are more appealing than others, and glass eels assemble in enormous numbers at the mouths of these rivers in preparation for the uphill march. Gathered there, they make easy targets.

Fishes strike from below, birds plunge from above, all manner of hungry animals feast on the defenseless glass eels, also known as elvers. People also stalk them, stretching nets across river mouths and scooping up juvenile eels by the millions. Since Aristotle’s time and before, people around the world have captured eels for food, but today in the state of Maine a pound of elvers can fetch more than $2000. Mostly the elvers are shipped to Asia, where aquaculture programs raise them into adults for sale to fish restaurants and sushi shops. In part due to this booming demand, eel populations worldwide have plummeted. European eels are now critically endangered, their numbers having fallen by 99 percent since the early 1980s.²⁵ Once they made up as much as half the fish biomass in freshwater ponds and streams, an abundance almost unimaginable today.²⁶ American eels—who, like cod, helped the Mayflower pilgrims survive in their new land—are faring little better, now listed as endangered.²⁷ Fishery catches of adult eels are sternly managed around the world in an effort to rebuild their populations, and glass eel harvests have been banned in all but a select few streams. For eels, fishing is not the only threat. Widespread installation of dams, diversions, dikes, power stations, and hundreds of other structures that interrupt river flows also block downstream eel migrations.²⁸ Industrial chemicals like PCBs leach into freshwater systems and are gradually absorbed by eels, coming to rest in fatty tissues. During their oceanic migration, fat reserves are mobilized to power the journey, and those toxic chemicals exact a heavy toll.²⁹ And like most fishes, eels suffer the attentions of parasites, including one worm that invades the swim bladder, impairing the eel’s buoyancy and ability to swim properly across the wide ocean. For animals who spend so much time in both fresh and salt water, it is no surprise they are affected by the hazards of both worlds.

Little wonder, then, that the mysterious eel baffled Aristotle. He was stumped because it seemed impossible that a fish could live for so long without mating, could travel far from home to do so, and could show no signs of reproductive organs until the very end of its life. That they can swim halfway around the world to court, mate, and die is almost beyond comprehension. One theory postulates that the warm seas sought by eels were much closer a few tens of millions of years ago when these remarkable fishes evolved, because the Atlantic Ocean was much narrower. As the continents drifted, the Sargasso Sea slid further and further away but eels kept adapting to cross the ever-widening gulf, like ultra-marathon runners gradually upping their distance. Despite more than two millennia of study, to this day there is much about the life history of eels we do not know. Consider this: an adult eel has never been found in the Sargasso Sea, nor has any living person ever observed two eels mating. Slippery in action and origin, eels yet guard a few secrets; like an enchantment, mystery shrouds them still.

What Comes Down Must Go Up

Although the habit of migrating in and out of fresh water is rare (just 1 percent of all fishes do so), over 440 species in fifty-eight different families have adopted the diadromous lifestyle. Anadromy—breeding in lakes and rivers, like salmon—is more common than the eel’s catadromy, with one-third of species choosing this route to reproduction. Of no little significance is the fact that more than half of diadromous fishes are commercially important species, such as salmon and eels, shad and sturgeon.³⁰ This unique life history must provide substantial benefits to those species able to cope with the transition between two very different environments, but there is disagreement over the origin of diadromy. The leading hypothesis posits that resource availability enticed fishes to expand their watery horizons.³¹ Near the equator, ocean productivity is relatively poor while freshwater streams boast considerable resources. In these places, catadromy would have arisen as saltwater fishes invaded the land in search of more food. Conversely, near the poles, crystal clear rivers and lakes on land offer scant nutrition, but the seas are booming with productivity, tempting freshwater species to descend toward the ocean and the promise of a ready meal.

This explanation has a certain elegance, though not all diadromous species fit the pattern: both giant mottled eel and African longfin eel (A. marmorata and A. mossambica), for example, live near the equator.³² An alternative theory postulates that in cold latitudes fresh water would be invaded less frequently since ponds fluctuate dramatically in temperature and can even freeze solid. Others contend the abundance of saltwater predators make streams a safer place to rear young. Combinations of all the above likely apply, in varying permutations, to different fishes: if the cost of migration outweighs the cost of staying put, then adopting a diadromous lifestyle becomes advantageous. And, if the ocean is a pathway rather than a barrier, an additional set of benefits kick in. Take New Zealand, where half that isolated nation’s fishes (including eels) are diadromous.³³ Genetic evidence reveals that sea-swimming allowed species to colonize new streams around the main islands, bolster established populations that were declining, and re-colonize waters where local extinctions had taken place. Crossing the ocean even permitted mainland fishes, over geological time, to settle on remote offshore islands. The Australian longfin eel (A. reinhardtii), for example, appears to have reached New Zealand within only the last fifty years, having successfully swum over from the continent of koalas and kangaroos to reach the land of kiwis.³⁴ Where most freshwater fishes treat the ocean as a salt-ridden, poisonous barrier, diadromous species know an opportunity when they see it.

What may be considered a colonist on one continent, however, can be an invader on another. Take the alewife (many in the Great Lakes would add an emphatic “please!”). This innocuous-looking member of the herring family is a foot-long, silver-sided fish with a dark and shallowly forked tail, and a propensity to swim upstream in huge numbers. The alewife (Alosa pseudoharengus) is native to the northwestern Atlantic, where it routinely enters rivers of eastern North America for breeding: like salmon, it is anadromous. Unfortunately, one inquisitive alewife eventually discovered Canada’s Welland Canal, built in the early 1900s for shipping traffic to bypass Niagara Falls. Alewives seized an opportunity to circumvent the falls, which heretofore had been an insurmountable barrier to these underpowered little fish, and by the 1930s they had reached the Great Lakes.³⁵ Their population soared in this new freshwater universe, and soon they were the most abundant fish in Lake Michigan, exceeding half of all fish biomass.³⁶ Municipal drinking water intakes were routinely clogged by dense knots of alewives.³⁷ By 1974, commercial fishers were harvesting in excess of 20,000 tons annually, without so much as denting the population.³⁸ Ballooning schools savaged the larvae of resident fishes such as lake trout, a popular sport fish, whose numbers plummeted like a barrel tumbling over Niagara.³⁹ Another anadromous pest, the sea lamprey (Petromyzon marinus), also had entered the great lakes with devastating effect. Known as the vampire fish, these eel-like parasites attach a round mouth bristling fearsomely with teeth to the flanks of larger fishes and proceed to gnaw, tear, and slurp the life from their unfortunate victims. Lake trout, hit with a double whammy of predator and parasite, were headed for extinction.

But alewives and lampreys decimated their own food supplies, swiftly eating themselves out of house and home. Seasonal fluctuations in prey abundance, water temperature, and nutrient levels led to mass alewife die-offs: millions upon millions of fish corpses piled high on lake beaches where they rotted, to the considerable visual and olfactory distress of would-be sunbathers. Here was an invasive species in desperate need of control. Fisheries managers would eventually find a savior in two non-native species, chinook and coho salmon (Oncorhynchus tshawytscha and O. kisutch). Voracious predators in their own right but native to the Pacific Ocean, chinooks and cohos were stocked into Lake Michigan in the 1960s, and the other Great Lakes soon followed suit. Over the following forty years, nearly 1 billion salmon were poured into alewife-dominated lakes in the United States and Canada.⁴⁰ They soon became flagships of a resurgent sport fishing boom and took pressure off lake trout by making significant inroads in alewife numbers. Chinooks in particular devour alewives the way moviegoers plow through popcorn: in some years alewives made up more than 90 percent of chinook stomach contents.⁴¹ Bottom trawl surveys in Lake Huron showed alewife numbers sank by 50 percent in the 1980s, and by the early 2000s had nosedived by 99 percent.⁴² Eventually, the popularity of salmon sport fishing encouraged lake managers to maintain alewife populations as food to sustain valuable coho and chinook stocks. Today these Pacific and Atlantic newcomers have established permanent populations that oscillate in response to environmental factors and each other’s abundance. A new equilibrium has been reached, in a novel ecosystem that North Americans accidentally created but learned to manage for environmental stability and food production.

When European colonists first reached the New World, they nearly starved to death; arriving in winter, without agricultural know-how, or even farming tools, will tend to do that. But they were saved by the bounty of the sea. When the Mayflower pilgrims could no longer reach nearshore cod, they would rely on anadromous species that came to them. “In the year 1623 the Plymouth colonists had but one boat left,” wrote a historian in the early 1800s, “which then was the principal support of their lives, for that year it helped them for to improve a net wherewith they took a multitude of bass, which was their livelihood all that summer.”⁴³ Fortune, and migratory pathways, smiled on the pilgrims, as they had set up their colony near spectacularly rich runs of striped bass (Morone saxatilis). Also known as stripers, or rockfish for their habit of congregating and cavorting around river rocks, some robust individuals can weigh over 100 pounds and live up to thirty years or more.⁴⁴ Stripers are handsomely shaped, with a pointed nose and a deep belly tapering gracefully to a shallowly forked tail fin. Silver flanks are boldly striped from head to tail with eight or nine dark lines. Like sports fans wearing team jerseys, striped bass can herald their origin with colors: the dorsal side of coastal individuals is tinted olive green, while offshore residents exhibit more a bluish cast.⁴⁵ After reaching maturity (females in eight years, males in just four), they migrate into estuaries and up freshwater rivers to mate. Striped bass are impressively fecund, with the largest females releasing as many as 5 million eggs. Juveniles frolic in fresh water for one or two years, then make their way back down to the sea where they devour smelt, herring, alewives, and lots of crustaceans.⁴⁶

Reports of their abundance while running upriver are awe-inspiring, and it is little wonder that their bounty was once a mainstay of coastal dinner tables. Residents of Plymouth in 1637 gushed, “there are such multitudes, that I have seene stopped into the river close adjoining to my house with a sande [seine net] at one tide, so many as will loade a ship of 100 tonnes.”⁴⁷ Even in the 1960s researchers recorded “an aggregation of large striped bass forming a 4- to 8-foot-wide band along the east bank of the river. This band, which was formed by several thousand fish, was about 1,000 yards long.”⁴⁸ That this latter report was from California’s Sacramento River, where only 435 fish had been introduced a century earlier and 2500 miles from their native Atlantic, shows just how adaptable and prolific are striped bass.

As has been seen with cod, however, seemingly inexhaustible populations of fish can collapse after only a few years of overfishing. In the case of New England, the colonists soon conceded that striped bass was on the decline. In probably the first wildlife conservation statute enacted in North America, the General Court of the Massachusetts Bay Colony decreed in May of 1639 that “it is forbidden to all men, after the 20th of next month, to imploy any codd or basse fish for manuring the ground.”⁴⁹ In other words, no more grinding up stripers into fertilizer, something the pilgrims had also done with menhaden. Instead, striped bass would be protected solely as a food fish, and a delicious one at that. “The Basse is an excellent Fish, both fresh and Salte. They are so large, the head of one will give a good eater a dinner.”⁵⁰ Commercial fishing in the twentieth century unfortunately overwhelmed even their immense reproductive output, and numerous striped bass fisheries were closed outright in the 1970s. Strict catch limits were applied, and later modified to implement a “harvest slot”: only medium-sized fishes can be caught, a policy that protects both developing juveniles and large, reproductively important females.⁵¹ Populations today are rebounding to the delight of fisheries biologists as well as sport fishers.⁵² As far back as 1849, the exhilaration of hooking a striper was trumpeted, when guide books sang the praises of “the boldest, bravest, strongest, and most active fish that visits the waters of the midland States.”⁵³ It seems only fitting that anglers, whose annual licenses provide substantial funding for striped bass management, today play a key role in conserving a fish that has sustained Americans for centuries.

And Miles to Go before I Sleep

The Waters of this river is Clear, and a Salmon may be Seen at the deabth of 15 or 20 feet. Passed three large lodges on the Stard Side near which great number of Salmon was drying on Scaffolds.

—William Clark, Journals of the Lewis and Clark Expedition

They called the place Celilo, meaning “echo of falling water” in several tongues, and the thunderous roar of the cataracts could be heard for miles. Indigenous peoples had gathered at this site for some 11,000 years, making it the oldest continuously occupied settlement in North America.⁵⁴ Wishram, Wasco, Wyam, Chinooka, and many others were drawn to the broad river and its roaring waterfalls by a fish; more precisely, by the yearly arrival of millions upon millions of salmon. Nets the size of dinner tables were deployed on long handles from steep banks, dipped into roiling waters to catch salmon disoriented by the raw power of the falls. Chinook salmon (Oncorhynchus tshawytscha) can attain weights exceeding 120 pounds, and annual harvests at Celilo were turned into thousands of tons of pressed and dried fish.⁵⁵ A portable and eminently tradeable source of protein that could be stored for two years or more, preserved fish from winter salmon runs helped build a sprawling economy and some of the richest cultures in the world. When Lewis and Clark passed the area in 1806, on their return journey from the Pacific coast, they were astonished by the sheer size of Indigenous populations. Contrary to popular belief, theirs was not an exploration of a vast, empty continent; instead, the expedition found itself leapfrogging from one native settlement to the next, through a densely populated and intricately managed landscape where they were repeatedly rescued by the kindness and generosity of local tribes. At Celilo, they traded for fish and other goods side by side with people from Indigenous nations across the West. From ornamented shirts and deerskin moccasins to onions, horses, and tools, “all of those articles they precure [sic] from other nations who visit them for the purpose of exchanging those articles for their pounded fish of which they prepare great quantities.”⁵⁶ A born marketer, William Clark dubbed the place, “the Great Mart of all this Country. Ten different tribes who reside on Taptate and Catteract Rivers visit those people for the purpose of purchaseing their fish … and Such articles as they have not.”⁵⁷

Today, the bustling mart—and indeed the waterfall itself—is no more. Celilo Falls (also called Horseshoe Falls, or Columbia Falls for the name given its river by white settlers), plus an impressive series of downstream cataracts and rapids, were drowned by the construction of the Dalles Dam in 1957. Part of an extensive system of hydroelectric power production in the West, the dam is 200 feet high, nearly 9000 feet wide, and takes its name from a French voyageur term for rapids. On the eve of construction more than 5000 Indigenous fishers still plied their nets from nearly 500 sites along the steep banks.⁵⁸ But the salmon runs were soon finished, blocked by an insurmountable wall of concrete. Cold waters that drained from high mountain snowpacks, ideal for rearing juvenile salmon, would no longer flow unimpeded to the sea. Native communities on both sides of the Columbia were displaced as rising waters flooded fishing sites and market grounds. Although fish ladders were built for salmon migrating upstream, and a spillway added in 2010 for juveniles heading downstream, the dam remains a colossal impediment. For the salmon, not to mention Pacific Northwest native peoples, life would never be the same.

Most salmon grow to adulthood in the richly productive waters of the northern Pacific, devouring crustaceans and small fishes who are slurping a rich stew of plankton. But those planktivores also devour eggs, so salmon—like striped bass—enter the mouths of freshwater rivers and swim furiously upstream to reach mating grounds where their eggs can be deposited safely. There are seven species of Pacific salmon (all in the Oncorhynchus group like the chinook), separated by a continent from their cousin the Atlantic salmon (Salmo salar). In both oceans, these fishes grow from juveniles to brawny, powerful adults: some 95 percent of their weight gain occurs in the marine realm. Most salmon are shaped like muscular torpedoes, with dorsal and anal fins affixed fairly far aft, as is characteristic of strong, swift swimmers. The mouth is set slightly low on a pointed snout, and jaws are studded with sharp teeth befitting a carnivore. Body color ranges from greenish-yellow to silvery, depending on the species, as do diverse patterns of ornate spots, speckles, and stripes. Thick flanks drive powerful thrashes of a salmon’s shallowly forked tail, pink-orange muscles that provided abundant food to Indigenous Americans and now to diners around the globe. The exact color of salmon muscles reflects their diet and geography, seasoned with a dash of genetics. Astaxanthin, a carotenoid pigment (named after carrots), cannot be synthesized by salmon but is abundant in their diet of shrimp, krill, and other marine crustaceans.⁵⁹ Sockeye (Oncorhynchus nerka) and coho muscles are the darkest red, while some chinook harbor a recessive gene that programs for ivory-colored flesh; a few oddballs even show white on just one flank while the other is pink.⁶⁰

Assigning common names to living organisms can be fraught with confusion, and the words “salmon” and “trout” offer befuddling examples. There are salmon who skip migration entirely, remaining landlocked in fresh water their whole lives like some sockeye, but still they are called salmon.⁶¹ Meanwhile among trout, typically seen as permanent freshwater residents, there are a few species who undertake migrations to salt water, such as the rainbow trout (Oncorhynchus mykiss). Even worse, salt-inhabiting rainbow trout often are labeled steelhead salmon. The unfortunate reality is that there is no concrete definition of the word trout, a term applied with distressing inconsistency to various species of Oncorhynchus and Salmo. “Char,” another moniker for freshwater members of the salmon family (in the group Salvelinus), muddies the waters further since some char are bewilderingly referred to as “sea trout.” All these fishes, however, are similar in appearance, streamlined and sporting an extra dorsal fin near the tail (the adipose fin); all are predatory in both fresh and salt waters, but only true salmon will migrate from oceans up into streams and rivers.

After three to five years of growth, a seafaring salmon reaches full adult weight and is ready to reproduce. By the millions, passionate salmon males and females gather along coastlines, readying themselves for an upstream journey that can range from a brief, casual jaunt to an arduous migration. Some king salmon (a regal synonym for chinook, reflecting their status as the largest of all salmon) will travel up the Yukon River from Alaska to British Columbia, traversing nearly 3000 miles.⁶² Around the Pacific thousands of rivers once hosted salmon migrations, although dams and other obstacles have reduced that list to a fraction of its historical number. Regardless of the count, when salmon depart the vastness of the sea and enter river mouths, they are funneled from a dispersed life in an open environment into dense parades up a narrow freshwater boulevard. That concentration of living animals, passing by river mouths and rapids in immense quantities at predictable times is what made salmon the largest Indigenous fishery in the Americas. The Pacific Northwest was home to some of the most advanced native civilizations on the continent, largely because a year’s supply of salmon could be caught and dried in a few hard-working weeks, leaving abundant leisure time during which wood carving, weaving, bead art, dancing, dramatic storytelling, and other forms of culture could flourish.

Before oceanic salmon test themselves against a gauntlet of fishing nets and human-imposed barriers, they undergo significant physiological changes. They have spent years at sea, fattening and preparing for migration, and now they are ready to return home. Sockeye salmon may travel 8000 miles or more through ocean waters as they develop.⁶³ King salmon spend four years at sea traversing more than 10,000 miles, but all these fishes unerringly return to the precise stream in which they were born.⁶⁴ Magnetic sensory cells have been found in salmon skulls, a trait they share with eels, that enable them to follow compass bearings. But it is this fish’s sense of smell that enables them to find a freshwater needle in a saltwater haystack. Salmon possess exceptionally acute olfaction and just need a whiff of a few scent molecules from their native stream to find their way. Experiments comparing blinded salmon (wearing dark sunglasses actually) to those with their noses plugged by cotton confirmed that only those fish with unblocked nostrils were able to find the stream of their birth.⁶⁵ Other ingenious experiments with juvenile salmon revealed they “imprint” on their home stream, meaning they can sense lower concentrations of odors to which they were exposed as youngsters.⁶⁶ A superior sense of smell may not be the only course-plotting tool salmon have at their disposal: juvenile salmon can even detect the sun’s position, and thus celestial navigation likely plays a role.⁶⁷ Despite these tools and skills, some salmon will inevitably swim up a river that is not their own. Known as “straying,” these migratory wrong-turns actually provide considerable benefits, since salmon could never colonize new rivers nor restock declining runs if they exhibited only error-free navigation.

Once an adult salmon reaches the mouth of its natal river, it stops eating and henceforth relies wholly on stored energy (though this is not true of Atlantic salmon, who do return to the ocean after inland breeding forays). Just offshore, they wait for spring floods to scour away tidal sandbars, clearing a path from the sea. Upon entering the river, however, they are exposed to fresh water, a liquid as dangerous to them as salt water is to eels. To fight bloating and the loss of salt, salmon rely on special cells in the gills to actively take up salt; membrane proteins that pump salt from those cells surge in abundance as a salmon readies for migration. Meanwhile, kidneys work overtime to draw excess water from the bloodstream and manufacture a very dilute urine. Even in the bladder, additional salt is pulled from the urine before it is jettisoned back into the river.⁶⁸ Adapting to fresh water uses valuable energy, and a salmon will need every volt in its battery banks to power the arduous journey through currents, rapids, and waterfalls. For this reason, salmon entering rivers are at the pinnacle of physical condition, tuned for a marathon swim upstream, dramatic physiological alterations, and protracted battles on the mating grounds. Fishers who target salmon runs—whether modern-day commercial fleets, Indigenous netters, or hosts of bears, herons, and more—are catching majestic fish at their muscular best.

Longer and more strenuous migrations require more energy and are undertaken only by the largest species: chinook, chum (Oncorhynchus keta), Atlantic, and coho, all of whom can bulk up to 30 pounds or more. On their way upstream, all salmon fight against river currents that range from feeble to firehose. Their streamlined shape, which permits speed and acceleration during ocean hunting forays, now allows them to slip through the onrushing waters. Powerful contractions of thick flank muscles drive vigorous tail thrusts, propelling them upstream and occasionally launching them into the air. Salmon are famous for leaping up rapids and waterfalls, circus stunts engrained in their DNA by some 50 million years of evolution. In Idaho, chinook will climb to over 7000 feet of altitude, so powerful is the drive to reach the cold, fast-moving, highly oxygenated waters ideal for rearing eggs and larvae. Along the way they may hurdle falls 10 or 12 feet high in a single bound, the equivalent of a pole-vaulter clearing a bar 30 feet above the mat. Some fish make the jump in a single attempt, others fail at first then circle to regroup and try again. Many shrewdly take advantage of a rapid’s standing wave, just below where a waterfall strikes the river, a counter-rotating eddy that thrusts water upward into a wavelike fountain and serves as a springboard for the salmon’s vault. After days or weeks of surmounting such obstacles, the strongest and most fortunate salmon reach the end of their migration: the spawning grounds.

In cold upland streams and ponds, males arrive first and await females. Once on the scene, a female sets about building a spawning nest called a redd, a shallow trench dug in gravel (though sockeye redds can be 5 feet long and a foot deep). Females compete vigorously for the best nesting sites, where pebbles are just the right size, and current sluices just enough cold, oxygenated water overhead but not so much as to wash away the eggs. Meanwhile, males have adopted dramatic costume changes in preparation for the big dance. Sockeye and coho exchange their mantles of silver and gray—excellent camouflage in the open ocean—for cloaks of the brightest carmine. In sockeye, the head is repainted a contrasting greenish-yellow; in coho (known in the ocean as a “silver”), olive-green wraps the head and back; chum salmon turn mostly olive, with large maroon blotches on their flanks. Skin pigments are repurposed from pink muscle tissue, at some energetic cost, explaining why the meat of late-run salmon becomes deathly pale. Male sockeye and pink salmon (Oncorhynchus gorbuscha) develop a pronounced hump on their backs, responsible for the latter’s nickname of “humpy.” The jaws of many species become grotesquely prolonged and bent, with the upper maxilla twisted into a hook and overlapping a curled lower mandible (Pacific salmon species share the scientific name Oncorhynchus, Greek for “hook snout”). Transformed males begin to battle for the attention of egg-bearing females: bright colors serve as a proxy for an individual’s physical health, while the hooknose gives an advantage when fighting rival suitors.

After digging her nest, a female selects a mate, as best as one can in waters roiling with fish, then deposits eggs into the redd. Her chosen male rushes in to fertilize the eggs with milt. Moving upstream, the female digs another redd, the current carrying some of the excavated gravel downstream to cover the preceding nest. Meanwhile, some males who might not win by virtue of color or fisticuffs try a different strategy. Chum salmon can adopt female coloration in mere minutes, a disguise they use to slip past rival males and quickly fertilize eggs while the macho boys still strut and wrestle. Over the course of several days, females will lay hundreds or thousands of eggs (depending on the species) and spend their final hours protecting their redds until the eggs settle safely into the gravel. Then, her work complete, she dies. All around her, vigorous scenes of life’s origin mingle with tableaux of death as the cadavers of spent fish fill the breeding grounds, and then are swept downstream. Still, in death there is life, as the bodies of dead salmon provide important fertilizer to aquatic environments below, and a valuable food source to scavengers like eagles. In Alaska’s Wood River basin, salmon even sustain a flower, a petite herb related to parsley and known as kneeling angelica. Umbrella-shaped clusters of white flowers are pollinated by a carrion fly that lays its eggs on salmon corpses; each year, the plant times its flowering precisely to coincide with the salmon run and blooms within ten days of their arrival.⁶⁹

In the redd, half the salmon’s eggs will be eaten or die of their own accord, the remainder hatching into tiny larvae after a month or three. Of those, just a quarter will survive to become parr, juvenile salmon.⁷⁰ Despite these heavy losses, they are nowhere near what ocean-breeding fishes experience (as much as 99.9 percent of larvae)⁷¹. Upland lakes and streams have fewer predators than the sea, and the farther uphill one travels, the more scarce egg-eaters become. Parr remain in their birth waters for anywhere from one to three years before succumbing, like adult eels, to the call of the ocean. A few depart early, like pink salmon who quit fresh water nearly as soon as they hatch. Whenever they begin, all embark on the reverse journey of their parents, over rapids and fish ladders, until they reach the river’s mouth and taste salt water for the first time. Now silvery in color, the youngsters are called smolt, a word sharing roots with “smelt,” and referencing the extraction of equally shiny metal from ore. Some will gather in nearshore eelgrass for a time, relying on those protective meadows for safety and food until they are ready to venture into the open ocean. Curiously, many smolt enter the sea tail-first, as they find it easier to face the down-rushing river current and swim with slightly less speed, traveling gently backwards.⁷² It is perhaps fitting that these juveniles, in culmination of a two-generation journey covering hundreds of river miles, rejoin the ocean facing the same direction as their parents: upstream, toward their origin.

These days, regrettably, many parr never smell the sea, and many adults never reach the breeding grounds. Around the world, rivers have been managed for priorities other than fish migrations, and countless salmon stocks have vanished. Dams like the Dalles have blocked upstream and downstream movement. Logging dumped tons of sawdust into rivers before the practice was banned, and winter-cut logs were floated downriver in the spring, just in time to barricade the annual upstream salmon migration. DDT, before it too was banned, was sprayed widely over forests to control pest outbreaks, but it savaged aquatic insect populations on which the parr rely for food. Mine tailings blocked rivers. Livestock to this day disturb river bottoms and trample streamside vegetation. Irrigation returns water to rivers warmer, saltier, and with less oxygen. Outflow from power plants also heats rivers. Global climate change is doing much the same, raising the temperature of lakes and streams and lowering their oxygen levels, changes that alter the timing of migration,⁷³ raise rates of disease and mortality,⁷⁴ and inhibit juvenile development.⁷⁵ Pitted against this parade of iniquities, it is astonishing that salmon have survived at all. But tenacity and adaptability are salmon’s strongest traits, and survive they do. Along the way they have received a little help from their friends in fisheries departments, who annually rear hundreds of millions of salmon fry in hatcheries then release them into streams to boost wild populations.

Yearly salmon runs are still strong on the Copper River in Alaska, where shoals of the regal chinook have been stable for years, under the watchful eye of fisheries managers and commercial fishers. Sockeye in Alaska’s Bristol Bay also continue to provide bountiful but sustainable harvests, as do coho in the southeastern waters of that state. Alaska in particular has done well to conserve its salmon, codifying their protection in the state constitution and preemptively stocking rivers with hatchery-reared larvae. Whereas overfishing has decimated populations in some regions—the Connecticut River, for example, and countless others in eastern North America—careful management in a few rivers has ensured consistent stock sizes and stable catches.

In some ways, the solutions are easy. Easy to identify, that is, but far more difficult to put into practice. As far back as the early 1800s, what was required to save salmon was widely known. Oregon Territory’s 1848 constitution mandated that all dams across rivers known to host salmon must include a bypass for both upstream adults and downstream parr. Earlier still, in 1824, a review of the declining state of salmon in Britain outlined a remedy that applies just as well today: “Remove the obstructions and the fish locks; keep the fish to the natural stream; prevent all unsizeable and unseasonable fish from being taken; protect them during the fence days and let no fish be taken but by fair and legal nets … and we soon will have no reason to complain of the scarcity of salmon.”⁷⁶ Sage advice that unfortunately was largely ignored for 200 years. Today, despite renewed interest in removal of obstructions (nearly 2000 dams have been eliminated from US rivers), we are prophetically facing a scarcity of salmon, and many other marine fishes too, and we all have reason to complain.