The School Cafeteria

Anchovies, a family of nearly 160 species, are distinctive from their small schooling brethren: sardines, herring, and menhaden. Reaching just over a foot in length (though many species are shorter), they resemble the others in their silvery scales, slender frame with dorsal fin set about halfway down the back, and acutely notched tail. But they are readily distinguished by their face: an underslung jaw, downward-pointing mouth, and pronounced snout have earned them the uncomplimentary epithet of “pig-like.” That snout contains the poorly understood rostral organ, a dense agglomeration of sensory antennae that puzzle scientists to this day. The perplexing organ is packed with neuromasts, sensory cells that may give anchovies a refined ability to sense minute water movements ahead of them; in ancient fishes like coelacanth, however, the rostral organ confers the ability to sense electrical fields, like an on-board voltage detector.¹¹ This sensory apparatus likely helps anchovies detect the jittery swimming of their prey, skittish zooplankton like copepods, giving the fish an extra ability to anticipate their quarry’s frantic escape moves. Anchovies, however, are not celebrated for being predators. They are famous as prey, abundant and delectable. For a tiny fish, the attack of a predator must be terrifying. Five hundred pounds of fins and teeth hurtle toward you at blinding speed, and in the open water there is nowhere to hide.

Anchovies play an invaluable role in marine food webs, whether they like it or not. They are the linchpin that connects the luxurious productivity of ocean plankton to the magnificent diversity of predatory fishes. On land there is nothing comparable: a small animal that grazes on tiny particles and is a mainstay food source for hundreds of larger species. It would be as if jaguars, lions, tigers, and eagles all subsisted solely on a diet of mice, and if those tiny rodents were so numerous as to carpet the plains with murine abundance (incidentally, a cluster of mice equivalent to a school of fish is charmingly called a “mischief of mice”). Unsurprisingly, anchovies are not particularly fond of their role as everyone’s favorite menu item in the ocean’s cafeteria. On their own, they can neither hide from an inrushing tuna or swordfish, nor can they outrun these muscular marauders. They can attempt the C-start maneuver, violently folding their body in half when a predator attacks, then rocketing into a 90 degree turn with an explosive contraction of the flank muscles. This escape reflex is aided by oversized neurons in the hindbrain known as Mauthner cells that can transmit impulses in as little as 10 milliseconds, ten times faster than the proverbial blink of an eye.¹² But a small fish is soon outpaced, so they have instead embraced a collaborative tactic to better their odds: swimming in mesmerizing, swirling schools that bob and weave around the thrusts and jabs of hungry predators.

Schools come in three flavors. Loose aggregations of fish that swim together, but without highly coordinated movements, are known as shoals. More tightly packed groups oriented all in the same direction are called polarized schools: changes in pace or course are mimicked instantly by their neighbors. Every turn, surge, dive, and about-face seems to be made by the entire school simultaneously, like a well-rehearsed ballet company. Fish may transition smoothly between these two flavors of schooling, as they continuously weigh the anti-predator benefits against the cost of feeding near schoolmates who would happily steal your lunch. But when the threat of attackers is imminent, a third form emerges. The panicking school retreats into itself, spaces between the fish shrink, and the densely swirling mass coalesces into a spinning sphere called a bait ball. The name was applied by fishermen who dip nets into such balls to catch bait for their hooks, an example of how a defensive strategy against one threat, predatory fishes, can leave anchovies at risk from another, fishing boats.

A catalog of benefits is delivered by schools to their enrollees, both offensive and defensive. If a predator strikes, each school member can just cross their fins and trust in the dilution effect: attackers are more likely to chomp any of a thousand schoolmates than you, the ultimate example of safety in numbers. But predator detection is a key advantage of schools: a few thousand eyes are more likely to see an incoming marauder. Characteristic movements by the sentinel reverberate swiftly through a polarized school, an alarm that travels up to seven times faster than the predator itself.¹³ This communication advantage is known as the Trafalgar effect, after the battle of the same name during which Admiral Nelson used signal flags to inform his fleet of enemy tactics.¹⁴ Schools and bait balls can also confuse their attackers, whether they are nearby or far off. From a distance, tightly packed clouds of anchovies may resemble much larger organisms, perhaps a shimmery whale, something a mackerel or tuna might not dare attack. If those predators do approach more closely, a different confusion effect sets in, the dizzying challenge of focusing on a single individual. When there are thousands of anchovies eddying around you, it is nearly impossible to lock on to just one to pursue and strike.

It is easy to see why small, defenseless fish so readily form schools and swim in such tight companies. But unlike a ballet, a polarized school has no choreography. Rather, each fish detects the movement patterns of his or her nearest neighbors and reacts accordingly. The school itself is referred to as an emergent phenomenon, one that arises from individual fish obeying a surprisingly simple set of dance rules. Schooling fish rely on their hyper-responsive vision to trigger those rules, but another sensory system is responding, one that is peculiar to fish and works only in a watery world.

Seawater is about 800 times denser than air, and it transmits waves of pressure far more effectively. Marine researchers working above the Arctic Circle in the 1960s could detect small underwater explosions at a distance of more than 700 miles, and there is evidence that a whale singing in Newfoundland can be heard by another in the Bahamas, over 2000 miles away.¹⁵ Fish can hear quite well, but they also can detect vibrations in water that are below the threshold of sound. A unique network of pressure sensors, whose origin dates back more than 400 million years, allows fish to perceive and respond to minute movements of water produced by neighbors, prey, or attackers. The network is known as the lateral line system, because it manifests in most fish as a fine stripe down each flank. It is an unfortunately pedestrian name, akin to calling our own sense of ear-mediated hearing the pink flap system.

The streak of the lateral line is on closer inspection composed of a meandering row of fine dots. Each is an opening to an internal water-filled canal studded with tiny, finger-like projections called neuromasts. Vibrations in water outside the fish reverberate into the canals and tickle a dunce cap of fine hairs perched atop each neuromast. The slightest deflection of these hairs triggers a nerve impulse that registers the velocity, and direction, of the vibration. Fish neuromasts can detect the faintest of water pressure waves, and they are as much as twenty-two times more sensitive than our own fingertips.¹⁶ Their resolution is also astonishing: blind cave fishes, who rely wholly on lateral line signals, can distinguish objects just four one-hundredths of an inch apart.¹⁷ So acute is this system that a fish can feel the movement of its neighbors and follow the rules that convene a school, even if it is fitted experimentally with blinkers covering its eyes.¹⁸ Fish can school using only vision, if their lateral lines are severed, but their ability to synchronize the speed and acceleration of their neighbors suffers.

Many of these experiments were performed on fishes that shoal and school in small numbers, a handful to a hundred. But anchovies and their cousins, in whose massive schools millions of swirling and turning fish are enrolled, require even more acute detection of changes in their neighbors’ speed and direction. In these small schoolers, the lateral line systems have been enhanced in myriad ways to achieve extraordinary sensitivity, rivaling even Spiderman’s.

First, the sensory canals that normally stretch along the flanks are concentrated around the head, where they are better able to read the movements of schoolmates up ahead, and where they can transmit signals that much more quickly to the nearby brain.¹⁹ The canals also branch and braid around the eyes and are linked to the inner ear, where they may feed signals into the auditory system. Some species evolved connections to the swim bladder, a gas-filled sac inflated for buoyancy control, but which can amplify the vibrations resonating from outside, like a taut drum.²⁰ Anchovy’s distant relatives, the longfin herrings, even have modified ribs, with small cavities inside them; the chambers’ small size may extend the range of frequencies that can be detected.²¹ Many species also possess mysterious inflated canals inside the skull behind the eyes, called bullae, that also connect to the swim bladder; it is not known whether the bullae send signals to the ear, or to the sensory canals, or both.²² It is clear, however, that the linked network of canals and hollows helps transmit and magnify vibrations, like the sound of a saxophonist echoing through the tunnels of a subway platform. Small schoolers have packed a lot of technology into their tiny heads, which operate as some of the keenest motion detectors on Earth. And yet, their predators have a few tricks up their proverbial sleeve as well.

Crashing the School Dance

I can see no limit to the amount of change, to the beauty and infinite complexity of the co-adaptations between all organic beings, one with another.

—Charles Darwin, Origin of Species

When one fish evolves a behavior, like schooling, that protects them against such marauding predators as swordfish, the hunters do not just fold up their tents and go home. Instead, they counter with novel hunting strategies of their own to disrupt the defense. The schoolers then respond in kind, and the cycle of coevolution between assailant and quarry takes another turn. Schools today are the refined result of millennia of adaptation and counter-adaptation, but their defense can be breached by even one new innovation. And predators are innovating all the time.

Many predators hunt in packs, the better to disrupt schools of prey. Spotted weakfish (Cynoscion nebulosus) prey on menhaden, small schoolers in the herring family, and have adopted a coordinated attack strategy. Menhaden meet the thrust of a single weakfish with a school response known as the fountain maneuver, in which the ball of menhaden flees the weakfish, then splits and turns to swim past it, then turns again as a reassembled school behind the bewildered attacker.²³ But spotted weakfish have been observed gathering in small phalanxes and charging as a compact line. The school, when faced with multiple predators, becomes fragmented and discombobulated and can no longer communicate and respond smoothly (the Trafalgar Effect is negated).²⁴ Indo-Pacific sailfish (Istiophorus platypterus) also hunt in groups, with one powerful attacker after another hurtling through schools of sardines, like a relay race. Though not all charges yield a mouthful of prey, nearly every sailfish manages to injure a few sardines as it plows through the school slashing its sword-like bill. The accumulating injuries wear down the school’s defenses, as wounded fish tire or fail to swim in synchrony; once this happens, the sailfish are increasingly able to pick off sardines from the battered school.²⁵ Other fishes, like tuna or silky sharks (Carcharhinus falciformis) will gather in massive hunting parties of a hundred individuals or more and literally herd and harass their prey into tight bait balls. Once the prey, quite often anchovies, are swirling in a compact sphere, the hunters will slam through the middle of the school, again and again. While you might think the center to be the safest, predators have responded to this strategy, and several species specialize in aiming like an arrow at the heart of the target. Their repeated body blows result in a splintered school, and some well-fed tuna.

Even without a squad to assist the hunt, open ocean predators have developed a toolshed of techniques to overcome the defenses of small schoolers. Sailfish, when not hunting in a group, rely on a creative method that takes full advantage of their long, distinctive bill. A sailfish creeps slowly to the wall of a bait ball, then delicately inserts its bill into the churning fish, so gently that they swim along unperturbed. The sailfish then selects a likely target and taps it lightly.²⁶ This must come as something of a surprise to the sardine. One moment you are swimming happily among thousands of mates, the next a 1000-pound predator with a 3-foot spear is poking you in the flank. If the disoriented sardine loses concentration and disengages ever so slightly from the school, all advantage is lost, and the sailfish takes it in a single gulp.

Another solitary hunter is the thresher shark, a distinctive species whose tail sports an impressive, scythe-like upper lobe nearly as long as the entire rest of the body. Threshers scour deep blue seas for schools of sardines, but if they attack with a direct charge, the school pulls the fountain maneuver and the shark comes up empty. Instead, a thresher will swim alongside the school, fold its body almost in half, and let fly with a powerful slap from the tail. So abrupt and powerful is the tail’s whipping motion that the tip reaches speeds of nearly 50 miles per hour.²⁷ Sardines clobbered by this rubbery lash are stunned or killed outright; the thresher wheels quickly once the slap has done its work, to scoop up its hapless victims.

The evolutionary struggle to defeat schools may have even played a role in the coloration of ocean predators. Researchers from the University of Cape Town noticed a similarity between school-hunting animals as unrelated as striped dolphins and African penguins.²⁸ Both move quickly through the water, both attack schooling fishes, and both are marked by distinctive black-and-white stripes running from stem to stern between black backs and white bellies. The conspicuously streaked penguins had been observed swimming rapid circles around small schools which then mysteriously disbanded: the school depolarized, leaving the schoolmates swimming higgledy-piggledy, unprotected, and ripe for the taking. In an ingenious laboratory experiment, the researchers menaced schools of anchovies with various penguin-like facsimiles. The anchovies, swimming in a close-knit school, reacted not at all to a translucent plastic model. When rushed by two-toned, black-and-white version, the school split in the fountain effect but largely continued their coordinated swimming. But, when a realistically striped replica was sent into battle, the school depolarized in two of every three trials and could not continue swimming in unison. The researchers theorized that the visual stimulation from the fast-moving stripes may overload the anchovies’ nervous system with information: perceiving the stripes took up so much sensory bandwidth that the little fish were unable to adequately process their neighbors’ positions, and the school collapsed. In other words, the penguins were hacking the anchovy security network.

Just as the strategies of predators continue to evolve, so too have the tactics of the small prey who are themselves hunted by schooling fishes. Copepods, amusing little crustaceans that row through the water with two tiny oar-like arms, are one of the favored targets of small schoolers. Sardines, anchovies, herring, and more dine voraciously on them. The response by copepods has been to develop a lurching swimming style: they jump sideways in the water, by slashing just one of their oars, to escape an onrushing herring’s maw. In response, juvenile herring coordinate the distance between each fish so the hunting school forms a grid matching the distance a copepod can jump.²⁹ A little crustacean sidesteps one oncoming herring only to land precisely in the path of the next, literally rowing from the frying pan into the fire.

Another, positively brilliant defensive innovation evolved in plankton as far back as 400 million years.³⁰ When set upon by a school of hungry fish, some plankton glow with a blue-green light. This bioluminescence, powered by the interaction of the devilishly named compounds luciferin and luciferase, is nearly the same as the light of fireflies (beetles, in truth). When activated by the roiling waters of an attacking school, the plankton’s glow illuminates marauding fish like security lights around a warehouse. Now the tide of battle has turned: the erstwhile predators become prey themselves, as the light summons even larger fishes to feast on them. Mackerel, tuna, sharks, and more home in on the glowing waters where they are sure to find anchovies, herring, or sardines. Plankton plying this so-called burglar alarm strategy take advantage of the adage “the enemy of my enemy is my friend” to gain some relief from the torment of their schooling hunters.

Follow the Red Herring

There is no family of fishes and no group of aquatic animals that contributes so largely to the support of the human race as the herrings.

—Hugh M. Smith, King Herring

Although schooling behavior evolved in anchovies, herring, and their relatives primarily to limit their own losses to predation, there is one predator on Earth that has turned the stratagem against them. For several thousand years, fishing boats have sought out schools of fish, encircled them with ever-larger nets, and hauled them out of the water to feed people and industry. Enormous catches are converted to fertilizer, fish oil, and protein for a hungry planet. And just as vast populations of anchovy made Peru and Chile into fishing powerhouses, the vast schools of herring that ply the northern seas built mighty empires in Europe and led others to their downfall.

Herring, despite all the trouble they have provoked, are handsome and unassuming little fish on first glance. They lack the pig-nosed snout and underslung chin of their anchovy cousins, sporting instead a slightly protruding lower jaw that hinges in front of, rather than behind, their eye. Herring resemble other small schoolers in their silvery color, forked tail, and elongated body form. They reproduce quickly, and in large numbers, and usually swim in schools. They favor cooler and more temperate waters like the North Atlantic, a distribution that has for centuries made them a target of European fisheries. They do exhibit a few odd characteristics that distinguish them, including the production of sound. Many fishes make sounds underwater, a phenomenon that fills coral reefs with clicks, static, booms, and honks. But herring are somewhat unique even among sound producers: they sneeze, and they fart.

It has long been known that a herring will make a sneezing sound when pulled onto a fishing boat.³¹ This may happen because of the release of air from its buoyancy-control swim bladder. Where many fishes inflate and deflate the bladder using gas dissolved in their blood, herring actually gulp air from the surface to puff up the swim bladder. Several fishes who favor nearshore waters do this as well. To prevent air escaping the bladder by seeping across its walls, the lining is impregnated with none other than guanine, the compound that made small schoolers famous, and which has the added value of slowing gas diffusion. When a herring is caught and hauled rapidly to the surface, the tightly sealed swim bladder can expand rapidly due to the reduced water pressure, akin to taking a party balloon on an airplane. The only route to relieving this pressure is by expelling air through their mouth and nostrils, which may explain why some herring give a wet, explosive blast not unlike a sneeze.

There is another route for releasing pent-up air from the swim bladder, and it may explain the unique and slightly comical explosive blasts herring emit underwater. For years researchers detected repetitive ticking sounds made by herring. High resolution cameras revealed that some species expel a bubble from the anus that coincides with the ticking.³² To make matters even more amusing, the acronym for the fast repetitive ticking, or FRT, sounds an awful lot like “fart.” Whoever said scientists were humorless had not spent time with FRT-specialists. Those sounds, however, almost certainly have a use beyond entertaining researchers and fishing boat crews. Herring most likely are communicating with their schoolmates, producing what ornithologists refer to as a contact note, something that says, in effect, “I’m over here.” In the dark, Pacific herring (Clupea pallasii) emit more FRTs than in the light, suggesting the ticking sounds play a role in maintaining group cohesion in the absence of vision.

Despite, or perhaps because of, these odd and amusing characteristics, herring have been much beloved across Europe, provided an invaluable source of food for centuries, and served as a wellspring from which numerous colorful expressions have been drawn. When eaten fresh, they have a strong flavor due to their high oil content. But in older times, pungent fish were the food of the poor, and a plateful would send rich lords and ladies into paroxysms of nose-clutching. The expression “dead as a herring” referenced the indubitably deceased nature of a stinking fish. That powerful smell was occasionally used to distract hunting dogs, putting them off the scent of the fox or quail, a practice that gave rise to the term “red herring,” meaning something that draws attention away from the matter at hand. Sherlock Holmes mysteries, for example, relentlessly introduce seemingly panicky or guilt-stricken characters who serve as mere distractions while the true killer lurks in plain sight.

A herring became “red” when it was preserved in salty brine, a common preservative that allowed the highly seasonal catch to be shipped across Europe or stockpiled for leaner months. When butterflied and brined whole, a herring becomes a kipper, that famous fishy addition to English breakfast or high tea. Sometimes, kippers were made by simply gutting a herring and hanging it on a line to dry, a method much used when salt became scarce. Someone in England who had been framed might say they were “done up like a kipper,” where the American equivalent would be “hung out to dry.” And in London, when Parliament banned salmon fishing in the River Thames for several months each year, locals relied heavily on dried herring: the expression “kipper season” came to mean any period when work is scarce and belts must be tightened.

Herring have even influenced European geography, with numerous cities having been sited just to take advantage of plentiful spawning and feeding grounds, counting Copenhagen and Amsterdam among them. Other regions rose to prominence thanks to salt mines that supplied brine to preserve the catch. Thus the map of Europe to this day is imprinted with the atlas of the herring industry. So sought after was the wealth tendered by herring fisheries that conflicts inevitably broke out, between boats and towns and even nations. The 1429 Battle of Herring pitted French forces against a British caravan bringing supplies to English soldiers, then laying siege to the city of Orléans.³³ The caravan was loaded with herring and outwitted the attackers by literally circling the wagons before springing a counter-offensive. Those fish would go on to fuel a victory that marked the turning of the tide against the French in the Hundred Years’ War, and incidentally Joan of Arc’s first defeat in battle.

Hundreds of years later, changing sea temperatures and currents have conspired to shift the spawning and feeding grounds of many commercial species of fish and have provoked renewed hostility between fishing nations. In 2013 the Faroe Islands announced its intent to triple their allotted herring quota because the fish were becoming more abundant and staying longer in their national waters. The United Kingdom and the European Fisheries Council responded angrily to this unilateral cornering of a shared fishery and imposed import bans that crippled the tiny nation’s industry. Negotiations eventually resolved the issue, but Senior Fisheries Biologist for the Faroe Islands Kjartan Hoydal noted wryly, “climate change will break up all agreements—there will be chaos.”³⁴

The value of herring was not always measured just by the pounds of stored food it provided, or by its contribution to national treasuries. Herring for many years constituted an important source of oil, fertilizer, and even explosives. Before the advent of widespread electrical grids, Norway powered street lights with herring oil pressed in large factories that dated back to the 1800s. This habit, so valuable in a northern country with long dark winters, persisted in many isolated towns until the 1950s. After the oil was squeezed out, what remained of the fish was minced into fertilizer for farming, an echo of the Peruvian guano industry that long before had buoyed the fertility of overworked fields. By the mid-1900s fish rendering was so lucrative in Norway that it consumed 95 percent of the national catch.³⁵ Industry factories often tortured nearby residents with the overpowering stench of volatile compounds like trimethylamine, otherwise known as essence of rotting fish. But it was a different kind of volatility that made fish oil famous.

In 1847, Italian chemist Ascanio Sobrero discovered nitroglycerine, a compound that could be synthesized from nitrogen-rich fish oils. One of his fellow students was Alfred Nobel, who later built an immense fortune on the production of dynamite and used that wealth to bankroll the world-famous prize awarded annually in dozens of disciplines. Back in Norway, fish oil pressed in the Lofoten Islands was converted to nitroglycerine explosives during World War II, but the facilities were seized by the Nazis after they invaded the defenseless nation. One of the first wartime acts undertaken by the British armed forces after the heroic rescue at Dunkirk was bombing the Lofoten factories to prevent the Germans from controlling nitroglycerine and using it against the Allies.

As a general rule, only small and plentiful fish are destined for oil and fish meal rendering. Large species like tuna and salmon fetch better prices as fillets, steaks, and whole fish. But the expensive and tedious labor of gutting, deboning, and filleting pint-sized herring, sardines, or anchovies makes it much cheaper to process them by the ton. Thus fish meal and oil-rendering industries focus on small species that reproduce copiously and aggregate in easily captured schools. Those fishes produce huge numbers of eggs, and if conditions are favorable the offspring grow quickly to reproductive maturity. A single female herring can produce more than 30,000 eggs per year;³⁶ a sardine yields over 100,000 and may spawn every year for a decade or more.³⁷ The trick, however, is whether there will be enough food for all those fishy offspring once that multitude of eggs hatch. If phytoplankton production is high and there is abundant zooplankton to eat, the juveniles will survive their post-hatching hunger, and the population will boom in the following year. But, if conditions are unfavorable and the sea’s buffet line is empty when the larvae emerge, they are doomed to starvation and next year’s population will plummet.

Boom and bust cycles of abundance are typical of small schooling fishes. One year the ocean boils with huge schools, the next it is quiet and still. Fisheries have had to adapt, sometimes painfully, to the cyclical nature of the seas. One of the strongest drivers of ocean productivity is seawater temperature, and even modest fluctuations can cause populations to plummet, or shift, as seen in the case of the Faroe Islands. In Peru, fisheries biologists spotted an intriguing trend in the catch data. Poor harvest years were typically sandwiched between better years, and the collapses seemed to occur at regular intervals. It was the first clue that planet Earth was experiencing intermittent vacillations in ocean temperature, which we now know as the El Niño phenomenon.

A Tin Can Packed with Gold

In the morning when the sardine fleet has made a catch, the purse-seiners waddle heavily into the bay blowing their whistles. The deep-laden boats pull in against the coast where the canneries dip their tails into the bay.

—John Steinbeck, Cannery Row

Little sardines were once big business in northern California, making Monterey famous as the state looked to match the success of profitable canning operations in Europe. After an encircling net called a lampara boosted catch rates of these small schoolers, the state’s fishing boats landed more than 27,000 tons in 1917 and reached a peak of 790,000 tons by 1937.³⁸ But by 1952 the sardine population had plummeted, and the fishery utterly collapsed. The industry’s autopsy produced more vitriol than verifiable fact, with one side placing the blame squarely on unregulated overfishing and the other pointing a finger at unpredictable environmental shifts. The reality likely lies somewhere in the middle. California fishers had vehemently resisted all efforts to restrain their industry, despite warnings by the Fish and Game Division that quotas must be established to protect the catch. The fishery had boomed during a period in human history when it was inconceivable in some quarters that a natural resource could be exhausted, despite considerable evidence to the contrary (just ask the great whales).

Warm waters entice sardines northward, but when the seas chill they drift south and become outnumbered by cold-tolerant anchovies with whom they partly share the coastal waters.³⁹ California researchers concluded that “abrupt natural declines, similar to the collapse of the sardine in the 1940s, are not uncommon.” Sudden declines are also typical of herring and anchovy populations, so it comes as no surprise that an industry reliant on catches of these boom and bust species must be prepared to survive the inevitable lean years. Whether schools of sardines prosper or suffer depends not just on water temperature, but also on the abundance of preferred foods. During the late 1940s the waters off the California coast were cooling, forcing sardine schools to migrate farther and farther south, until they were out of the reach of cannery boats. Counts of sardine scales in seafloor sediments show a roughly sixty-year cycle between abundance and scarcity, one that has characterized the population for some 2000 years.⁴⁰ The availability of delectable zooplankton, including tiny shrimps and nimble copepods, also teeters between bountiful and scarce as water temperatures swing from warm to cold. When the seas are productive, sardines can be found in dense schools during the day, feeding in the upper water column. Those schools typically disperse at night, however, when each sardine charts its own course through the dark waters; at dawn, the school reassembles.⁴¹

Visual hunters like tuna, mackerel, seabirds, sea lions, and the like are the primary predators on sardines and their diminutive ilk. The collective defense offered by a school is highly effective during the day, but once those predators punch out for the evening, there is less need for the protection granted by enrollment.⁴² Zooplankton are also hunted by sight, with their predators—the anchovies and herring and sardines—eyeing these little motes as they bob beneath the sunlit waves and plucking them like cherries from a bowl. Consequently, zooplankton have evolved a feeding pattern of their own, in which they sequester in the dark depths by day, sometimes beyond 300 feet down, then ascend to the surface under cover of night to browse on a salad of phytoplankton. Photosynthetic algae, of course, must remain near the surface where life-giving sunlight penetrates. Thanks to the migration, hungry sardines can tuck into a more bountiful zooplankton meal near the surface at night than by day, often by several orders of magnitude.⁴³ Zooplankton’s daily pattern of vertical migration was first detected by Navy sonar experiments that found a dense layer lurking in the deep. Fears that the blob on their screens were enemy submarines prowling off the coast were dismissed when scientists discovered this so-called deep scattering layer was an innocuous carpet of copepods and other organisms that rose by night to feed and dove at dawn to safety. One can imagine the sonarman’s relief upon learning that the menacing subs packed with torpedoes were in fact innocuous crustaceans no larger than a flea.

In the early 1900s, when the waters off northern California were rich in both plankton and sardines, the cannery industry surged. Thousands of people were employed to crew fishing vessels, unload the catch, and process tons upon tons of sardines before they went into the tin. Early on, a small side business emerged to handle the discarded heads and innards, which were boiled down (rendered or reduced, in industry parlance) into fish oil and fish meal.⁴⁴ Rendered oil was used for soap, linoleum, and other products, while the meal was destined for chicken feed. A cottage industry even arose to turn sardine scales into pearl essence, the shimmery liquid that heralded the discovery of guanine.⁴⁵ But, as the labor cost of hand-prepping sardines for canning soared, the fishery shifted increasingly to rendering until it effectively swallowed the entire catch.

Sardines, like anchovies and other small schoolers, are rich in oil. It is part of what gives them their strong fishy taste, but it also dispenses a shoal of health benefits. The oils are a direct reflection of their diet. Zooplankton eat phytoplankton that often rely on buoyant oils to prevent them from sinking. The zooplankton accumulate oil with every bite, and when gulped themselves they pass those oils on to a sardine. One small serving of sardines provides loads of vitamin B₁₂, which supports a healthy nervous system. These little oily fish are rich in niacin (B₃) and B₂, along with many essential minerals. And they are packed with a now-famous group of oils known as omega-3 fatty acids. A health craze focused on omega-3 oils has swept the globe, making vast fortunes for suppliers, and spurring formerly quiet fisheries to pull an ever-increasing, and potentially unsustainable, number of small schoolers from the sea. Indeed, the very evolution of humans, of our brain capacity and even our speech, may be the result of an ancient history of eating seafood. And the poster child for the omega-3 craze, once fantastically abundant off the shores of North America, is the most important fish that nobody has ever heard of, the menhaden.

A Fish for Every Stalk

An acre thus dressed will produce and yeald so much corne as three acres without fish.

—Thomas Morton, The New English Canaan

Five or six million years ago, in a marsh in eastern Africa or perhaps on its southern coastline, apes began adding seafood to their diet.⁴⁶ Shellfish were easily collected, fish were abundant, and crustaceans could be plucked from the bottom. Wading into the water to reach this new and plentiful food allowed the apes to stand on two feet instead of four, buoyed as they were by the warm salt water. Life became a little easier, and more apes adopted the aquatic menu. Over time, their brains were nourished by the oils that little fish and mussels added to their diet. They may even have begun to dive, holding their breath to reach shellfish on the bottom, the newfound breath control encouraging speech to develop. Ample food supported larger gatherings, and stable societies began to emerge. Modern humans were born from apes because of seafood.

So goes the Aquatic Ape hypothesis, first presented to the world in the 1960s, and hotly debated ever since.⁴⁷ Proponents argue that the grassy savannas, often thought to be the cradle of civilization, lack sufficient omega-3 fats to unleash the rapid brain development that sparked the meteoric rise of modern humans. Opponents point out that much of the evidence is merely a coincidence of timing, leaving unresolved whether seafood made humans, or humans emerged and later chose a marine menu. Nonetheless, if one turns the clock of paleontology forward a few million years to the days of Neanderthals, even more evidence emerges. Paleolithic hominids living in northwest Spain discarded piles of shells, fish bones, and crab legs that would be the envy of any bib-wearer at a Louisiana seafood boil.⁴⁸ Grottos around Pinnacle Point in South Africa show stunningly advanced cave paintings from contemporary Neanderthals who also fed richly on abundant seafood. The reliability and abundance of those foods likely supported a more stable society, with sufficient free time to dedicate to art and other pursuits, a progression nicknamed the cognitive revolution.⁴⁹ Across the planet, the coincidence is striking. The earliest complex human societies on earth all emerged where fish and shellfish were plentiful: coastal China and New Guinea, Mesopotamia, coastal Peru and Mexico, and the upper Mississippi River valley.⁵⁰

Today, the health benefits of omega-3 oils are trumpeted by medical experts and industry advertising, echoed in a tide of books and magazines, and breathlessly amplified by celebrities, chefs, and social media stars. Despite the faddish hype, regular doses of fish oil do confer a wide range of genuine benefits. Of some 7000 people studied in the Netherlands⁵¹ and southern France,⁵² those who ate fish at least once a week were significantly less likely to develop dementia. The Mediterranean diet, first detailed in 1975, curbs heart disease, cancer, and diabetes, extends average life span, and reduces healthcare costs. The benefits are linked to the diet’s substitution of seafood for livestock, and replacement of butter by olive oil, which more closely resembles fish oil in its fundamental chemistry. Such correlations with marine-rich diets have since been refined, focusing on several omega-3 fats known as EPA and DHA (shorthand for their tongue-twistingly convoluted chemical appellations). These fats must be obtained from our diet, as the human body cannot synthesize them; they abound in the red muscle flesh of oily fishes like sardines and herring thanks to oil-rich plankton. EPA and DHA have been proven to promote fetal nerve cell development, tamp inflammatory reactions, improve cardiovascular function, and even slow the advance of Alzheimer’s disease.⁵³ When grandmothers a century ago forced kids to endure a nightly spoonful of cod liver oil, they knew instinctively what they were doing.

Menhaden are attractive little fish, deeper-bodied than slender sardines, their silvery-purplish flanks overlain with a golden sheen and decorated with small black beauty marks. They were once so abundant in the Gulf of Mexico and North America’s eastern seaboard that in 1871 Captain Nathanael Smith described seeing a school “two miles wide and forty miles long.”⁵⁴ Adorably referred to as “bunkers,” and the juveniles even more endearingly as “peanut bunkers,” menhaden of all sizes are ravenously pursued by a medley of predatory fishes, from striped bass to sharks, porpoises to tuna. In a mad rush to escape becoming someone else’s lunch, they would occasionally throw themselves from the sea in such numbers that naturalist Mark Catesby reported, in the mid 1700s, a beach “covered with them at a considerable Depth, and three miles in length along the Shore.”⁵⁵ Menhaden’s prodigious reproductive capacity, and their ability to sustain so many predators, stems from their reliance on an equally plentiful food source, phytoplankton. Their algae-rich diet makes them plump and oily, prompting Catesby to describe menhaden as “excellent Sweet Fish, and so excessive fat that Butter is never used in frying.”⁵⁶ So abundant are, or were, menhaden that for many years their annual catch outweighed landings in America of all other fishes combined. Ponder that statistic for a moment. In 1955, for example, 1700 million tons of menhaden were netted, while the total catch of pollock, halibut, salmon, swordfish, tuna, flounder, perch, cod, snapper, striped bass, mackerel, and every other commercial fish taken in the United States added up to barely half that haul, at 975 million tons.⁵⁷

The oily nature of menhaden and a preponderance of small bones limited their commercial value as a food fish, until their worth as a source of oil and fish meal was discovered. Boiling a few fish in small kettles gave way to processing plants as early as 1850. Production rose as the collapse of the whaling industry left nations scrambling for a new source of oil, and by 1874 fish oil manufacture had outpaced whale oil by at least 50 percent. As in Norway, the discovery of petroleum displaced the fish oil industry for a time, but surging interest in the health benefits of omega-3s spurred the rendering factories to renew production and reach all-time highs. Signs of overfishing emerged as early as 1871, when a report by the newly founded US Commission on Fish and Fisheries concluded that populations had dropped to one-tenth of their levels in 1801. While a menhaden reduction industry association confidently announced that “the plenitude or scarcity of sea fish is wholly independent of the operations of man,” at least one fishing captain lamented, “for the last few years the entire coast line, from end to end, has been run over almost every day by the fishing vessels … have we not killed the goose that lays the golden egg?”⁵⁸

The scarcity of menhaden reverberated through the predators who relied on them, attracting the attention and provoking the ire of the sports fishing community. When striped bass, weakfish, bluefish, and others began to disappear from coastal waters, a coalition emerged to fight the rendering industry. Lawsuits, legislation, countersuits, and protests stretched on for decades, and the fight continues to this day. Eventually, all states north of Virginia banned entry by the reduction fleet. Even within Virginian waters the average weight of captured menhaden fell to a mere 6 ounces: juveniles were all that remained. In 2005, the Atlantic States Marine Fisheries Commission placed a cap on rendering catches of menhaden; however, in a cruel twist revealing the cloakroom power of the industry, that cap was set equal to the average annual catch, and thus represented no reduction whatsoever. Finally, after widespread public outcry the same Commission cut harvests by 20 percent in 2010. By 2017 the menhaden, their predators, and the ecosystem they compose were showing distinct signs of recovery, evidence that with proper fisheries management the fish oil business, sports fishers, and the marine ecosystem can coexist.⁵⁹

As far back as the early 1800s, the oil-rendering plants were faced with a problem: what to do with the flattened menhaden bodies after the oil had been pressed from them? The answer had been provided two centuries earlier, when the pilgrims who settled in New England were saved from starvation by a Patuxent man, and an unknown fish. Tisquantum, whose name was shortened and anglicized to simply “Squanto,” may have been the last of the Patuxent. Its members, and nearly all of the broader Wampanoag tribal confederation to which they belonged, had been ravaged by diseases presumably brought by the colonizing English. The pilgrims were poorly equipped for their adventure, knowing almost nothing of farming, carrying few seeds, and virtually no tools. Tisquantum took mercy on them, a charitable display given the suffering his people had endured, and introduced the white settlers to a fish he called munnawhatteaûg, a name from the Algonquin language meaning “that which manures.” The name, soon shortened to “menhaden,” was apt. Tisquantum taught the ersatz farmers to plant corn seeds in a mound of earth, and to dress that mound with a few menhaden as fertilizer. Soon, corn crops flourished, and the colony was saved from starvation by a man whose own people had been decimated.

Meanwhile, out at sea, menhaden, sardines, herring, and anchovies continued to convert plankton into vast schools of small, oil-rich fish. Seabirds continued to feast on their abundance, as did sea lions, sharks, and swordfish. The erratic and capricious nature of ocean productivity, however, meant those seabirds who had built towering mountains of guano would suffer inevitable years of tragedy. The famine that threatened the ill-equipped pilgrims could also devastate animals during hard-luck seasons. Amid the 1982–1983 El Niño event, some 8 million boobies, pelicans, and cormorants in Peru, a staggering 85 percent of the population, died from starvation.⁶⁰ Under the waves, predatory fishes who rely on small schoolers are bound to come up empty when shifting conditions convert last year’s bountiful buffet into this year’s food desert. Over time, mighty hunters of the open ocean, like tuna and sailfish, evolved to roam vast waters tirelessly and efficiently, pursuing far-flung schools thanks to body plans, musculature, and sensory systems all finely tuned to scour the seas for an elusive feast.