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Sea Change: How Can We Help Oceans Recover?

Can we tug the right threads to fix the ocean's food webs?
gulf-of-california



Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC

Based on Telling Our Way to the Sea: A Voyage of Discovery in the Sea of Cortez, by Aaron Hirsh. Farrar, Straus and Giroux, August 2013.

On a cloudless morning in late summer, five college students climbed from the sandy shallows into the open hull of a panga, a small skiff powered by an outboard motor, and departed the fishing village of Bahía de Los Ángeles, on the Sea of Cortez. Ordinarily, they would have gone out on the water with me—I was teaching their field course in ecology and evolutionary biology—but this was their day off, and they had hired a local to take them fishing.

From the stone terrace of the Vermilion Sea Field Station, I watched the boat carve a white V through placid water, heading straight toward the sun. It was early yet, and the small desert islands, the angels of Bahía de Los Ángeles, were dark silhouettes, afloat at the midline of molten sea and fiery sky. Five hundred feet from the beach, the outboard fell silent and the boat glided to stillness. Through binoculars, I watched my students drop fishing lines over the rails. At first I worried that their driver had decided to save gas, and this was to be their fishing trip. But when I saw a line come up twitching with a four-inch silvery fish, I realized they were merely gathering bait. After they had reeled in several dozen small sardines, the outboard started again, and they headed toward the islands and out of sight. I know what happened next because they told me about it later, when they returned to shore.

In the shadow of Isla Piojo, they caught two splendid yellowtail. Then came a third strike. The rod bowed and shuddered, but the young woman holding it managed to crank the line slowly in. From the way the fish was fighting, the guide judged it to be another large yellowtail. And indeed, when it came nearer the panga, he saw the flash of a silver flank before the jack dove hard, as they sometimes do when they first catch sight of the boat. Then, all of a sudden, the fighting ceased. Lamenting the loss of the big one, the young woman slipped the rod's long handle back into its holder.

Strangely, though, the rod remained ever so slightly arced, and several seconds later, the reel shrieked as line dragged out. With everyone, including the guide, taking a turn with the rod, the line was eventually reeled in. And when at last the guide plunged his gaff into the water, what he levered over the boat rail and let spill into the bow was a five foot squid, its arms writhing like a nest of snakes, the tubular body flashing blood-red. The guide clubbed it several times between its round, watery eyes, and finally it went still, the mucosal red skin fading to milky white.

A week later, back on campus, I received an alarmed email about another strange occurrence aboard a fishing boat, this one thousands of miles away, off the east coast of Japan. On the deck of Diasan Shinsho-maru, a ten-ton trawler, three crew members realized something was wrong when their winch creaked and groaned. Leaning over the rail, they saw the problem: the gathering net appeared to be full of slimy brown mud. Only it wasn't mud. It was jellyfish. Each creature was at least three feet across, and there were hundreds of them. The winch complained more loudly, the ship listed toward the laden net, and then capsized, tipping the trawlermen into the sea.

At first look, these events appear unconnected. They occurred on opposite sides of the planet. On the tree of life, Humboldt squid are as remotely related to Nomura jellyfish as we are. And yet, in another sense, the incidents are linked. They are signal cases of a phenomenon that has begun to unfold with increasing frequency in the world's oceans: The impacts of fishing are propagating through oceanic ecosystems in unpredicted ways. In the Baltic Sea and the South China Sea; in places once known for cod and others known for sharks; in the most productive waters and those less prolific—in short, all over the world, oceanic ecosystems have lately been tilting into new and different arrangements. Unexpectedly, some of these novel configurations seem to be stable in their own right. Various words have been used to describe the striking property: homeostasis; hysteresis; a certain dreadful stickiness.

Extinction, the bromide goes, is forever; but if ecosystems really can get stuck in new arrangements, it would mean that not only species, but whole natural systems, could be irrevocably lost. And such losses could be grave for a large number of people. Each year, humanity captures and keeps about 80 million tons of fish from the sea. It's a number worth staring at: 160,000,000,000 pounds, which provides almost half the world with at least a fifth of its animal protein. In many places, it is a resource without which humans cannot survive.

According to formerly dominant paradigms in oceanography and marine ecology, impacts—even our very substantial impacts—were not supposed to cascade through oceanic ecosystems, and such durable transformations were not anticipated. More broadly still, the ecological rearrangements, and especially the way scientists are now talking about responding to them, mark a shift in our basic relationship with the ocean. So this is a story of conversion not only in the sea, but also in the way we think of it.

~~~

One way to think of an ecosystem is with a diagram of its food web. In such a picture, each oval represents a species, or a natural grouping of them, and each arrow signifies what ecologists would refer to as transfer of biomass, but which you could just as well call eating.

What ecologists call trophic cascade has, I'm afraid, entered popular consciousness mainly through managerial missteps. Macquarie Island is a recent example. Halfway between New Zealand and Antarctica, Macquarie is a World Heritage Site, on account of a rich unusual flora and millions of nesting sea birds. Aiming to protect those birds, managers eradicated thousands of feral housecats. At first the plan worked: bird colonies grew. But soon, exotic rabbits, which had previously been hunted by housecats, began to do what rabbits are famous for. Proliferating, they mowed down the vegetation, facilitating erosion, which swamped and undermined bird colonies. This illustrates trophic cascade because a change at the top of the food web—trophe is Greek for food—cascaded down to levels below: the cat oval vanished; the rabbit oval swelled; the plant oval contracted. The mudslides are more of a metaphorical flourish on the basic concept.

Happily, not every example is so grim. In Yellowstone, the reintroduction of wolves stopped Elk from browsing down all the trees along riverbanks, and thus helped to restore healthy riverine ecosystems. But in both kinds of story—dispiriting and heartening alike—it's worth noting a common pattern: The population on any given floor of the food web behaves in contrast with those on adjacent floors, but in concert with those that are two floors away. Cats, on floor three, decline, and so do plants, on floor one. This pattern can hold true even in ecosystems with many levels, and ecologists look for it to see how an ecosystem works. If they find it, they say an ecosystem is subject to top-down control. For instance, cats or wolves, up above, determine the abundance of everyone below.

But that's all on land. Marine scientists have not traditionally thought in terms of trophic cascades and top-down control. Rather, they've assumed that the abundance on any given floor of the food web is determined mainly by the supply of nutrients from the floors below, and not by the impact of consumers up above. There are good reasons for supposing as much. In some parts of the ocean, food supply is patchy and sporadic; when there is food, there's too much for consumers to make a dent. Also, in a lot of oceanic ecosystems, many different consumers feast on any given floor of the food web. As a result, a contraction of one population near the top, such as yellowfin tuna, could be compensated for by expansion of another, such as albacore; and in that case, only changes in productivity coming from below will alter the overall abundance on the floors overhead.

The reason this distinction—top-down versus bottom-up control—is so important is that it drastically affects predictions about the impact of fishing. If control is from the bottom up, as oceanographers and fishery scientists have generally supposed, then the shock waves of our yearly 80 million ton scoop may propagate a short ways upward, to hapless animals like seabirds and seals, but will mostly be confined to the populations we actually fish. If control is top-down, however, our impact will cascade in complicated ways, causing floors below to become alternately crowded and empty, potentially compromising the food supplies of some species we fish, and broadly rearranging ecosystems. For any manager, then, the bottom-up consensus was enormously comforting.

~~~

And yet, despite all the good reasons trophic cascade ought not transpire in the sea, that's just what seems to be happening. Reading the literature and talking with marine scientists from a variety of disciplines, one gets the sense that the acknowledged domain of trophic cascades—the geographic area in which, according to most scientists, they are in fact occurring—has been spreading slowly but steadily outward, from small confined systems, like ponds and streams, out onto the littoral, across shallow reefs, and finally into the deeper waters of the ocean.

The very first demonstration of trophic cascade occurred in 1960, in little ponds, where the Czech ecologist Jaroslav Hrbacek observed that phytoplankton, the tiny photosynthetic organisms that fuel the food web in every body of water, actually increased their abundance in the presence of small fish. The fish, Hrbacek realized, were suppressing zooplankton, which occupy floor two in underwater ecosystems. In the late sixties and early seventies, top-down control was documented in several studies at the ocean's edge, and in 1974, a clear case of trophic cascade was detected in the Aleutian Islands. Sea otters had been extirpated from the islands about two centuries before, by Russian fur traders. Around islands where otters were now recovering, sea urchins were held in check, allowing a lush kelp forest to regrow. Where otters had yet to return, urchins kept the stone bare.

Even by the late nineties, however, top-down control was not generally considered relevant off the coast. John Steele, an eminent scientist at Woods Hole Oceanographic Institution, registered the view of most marine scientists when he wrote, in 1998, "The massive perturbations in marine fish stocks might be expected to have impacts on their food supplies, yet I do not know of any cases where this has been demonstrated in the sea."

But then, over the following decade, cascades came to light all over the oceans. The Aleutian cascade stretched out into open water when ocean-roving killer whales abruptly and mysteriously changed their behavior: they began eating sea otters, and just as one would have expected, based on the earlier findings, the effects cascaded down to kelp forests, many of which soon gave way to urchin barrens. Other cascades were found in the North Pacific, involving salmon, and then on both sides of the North Atlantic, involving cod. Ransom Myers, a prescient and industrious marine biologist who had for years been assembling a database tracking the world's fisheries, discovered that, off the east coast of the United States, fishing for large sharks had unleashed their prey, including rays, which were now demolishing shellfish beds. His study received much attention, not only because it was scientifically compelling, but also because the plague of rays had just brought an end to North Carolina's century-old scallop fishery.

Three days before the study was published in Science, Myers died, aged 54, of a brain tumor, but his ideas and database fed into many more publications. Among the most important was a synthesis led by Boris Worm, a protégé of Myers' at Dalhousie, and Ray Hilborn, a fisheries scientist at the University of Washington. Published in 2010, the work showed that, worldwide, the large deepwater fish that occupy the top of marine food webs had declined by 56%, while their prey—smaller, schooling fish—had actually increased by 143%, likely because they were released from top-down control. "Top-down interactions cascading from fishers to predators and their multiple prey species," the authors concluded, are "important structuring forces."

~~~

If this conclusion, held alongside the decades-old consensus that top- down control is unimportant in the oceans, looks like nothing short of a paradigm shift in marine science, what seems a bit mystifying is the creepingly slow conceptual migration that preceded it—the half-century it took for theories of trophic cascade to move from small ponds out to the open ocean. It's especially puzzling because, in truth, there were revealing data floating around all along—albeit in rather obscure places—and the relevant theory, too, was already in circulation. As early as the late seventies, for instance, a South African marine biologist had suggested that shark-exclusion nets around Durban's beaches had killed so many large sharks that their prey were proliferating. And in the mid-eighties, a group of mathematical ecologists, meeting to talk about fisheries, asserted that managers ought to pay more attention to threats posed by trophic cascade.

So why did it take so long for the idea to take hold? It's possible that the greatest intellectual success of late-twentieth century oceanography incidentally confounded thinking about top-down control. Beginning in the late-eighties, oceanographers realized that every few decades or so, entire ocean basins—the North Pacific or the North Atlantic, for instance—experience sudden shifts in their patterns of circulation, drastically changing physical conditions for the entire region. Oceanographers called these events "decadal switches" or "regime shifts." Unfortunately, ecologists had recently been using the term "regime shift" to describe what happens when you extirpate a top-predator and the effects cascade through the entire system. But obviously, the common term belies contrasting explanations of change. And dangerously, the two explanations confounded each other.

In the North Sea, for instance, a decadal switch—of the physical, oceanographic variety—occurred in the late eighties. But this was also a time and place of intensive fishing. So was the upsurge of herring due to shifts in the physical environment, or to the cascading effects of cod fishing? Here's an analogy that gets at the difficulty: imagine how hard it would have been to prove that global warming is caused by humans if, just as climatologists were struggling to get their message across, astrophysicists had made the fantastic new discovery that the sun sometimes shifts to hotter temperatures.

~~~

The coastal towns of eastern Canada, snug clusters of peaked roofs and weathered wood, tucked in rocky coves so as to be near the boats but out of the weather, are communities that cannot survive without their haul from the sea. So when the groundfish collapsed in the early nineties, and the government, intent on bringing them back, declared a moratorium on fishing cod, haddock, and pollack, the towns unraveled. In the first year of the ban, forty thousand jobs were lost, most by people with little to fall back on. Thousands of families up and left. Schools closed. Rates of mental illness rose.

All that by way of sacrifice, and still, the groundfish did not recover. Many took this as clear evidence that new physical conditions, ushered in by a decadal switch, had to be to blame; otherwise, why wouldn't the fish have rebounded? Moreover, a similar case of strangely stubborn collapse was unfolding, at the very same time, in the cod fishery of the Baltic Sea, so it seemed plausible that the parallel tragedies had their common origin in a vast, North Atlantic decadal switch. But the groundfish's failure to recover, it now appears, does not necessarily implicate a decadal switch, because it can also result from the inner-workings of a food web.

Kenneth Frank, at the Bedford Institute of Oceanography, was able to reconstruct the cascade that transpired off the coast of Nova Scotia. As groundfish numbers fell, their prey—herring, capelin, and sand lance—surged, causing a decline in zooplankton and an expansion of phytoplankton: a cascade through four full stories of the food web. Still, nothing in this picture suggests why the process did not simply reverse itself once the fishing relented. But researchers from Germany and Sweden, studying the Baltic catastrophe, recognized that the extended trophic cascade may have triggered another kind of change, a bit like a Rube Goldberg machine that, as its final step, opens a trapdoor beneath itself.

Looking at our diagram of ovals and arrows, you'd think an explosion of herring and their ilk would be a boon for cod, as it would send more food up the system. But what if the herring are not only feeding cod, but also competing with their young for food—or even making them into food? In that case, an unleashed herring population could prove disastrous for an overfished cod population: the herring provide more food than adult cod can possibly eat, but eat as many young cod as the adults can possibly provide. And now the trophic cascade, beyond resizing all the ovals in our diagram, has actually rewired the arrows: what was prey has effectively become predator. "Regime shift" is just the right term: a different species is on top, and it uses its newfound power to stay there.

It now seems likely that some rewiring has occurred not only in the Baltic, but also across the northern Atlantic, and elsewhere in the world, as well. In fact, it has probably contributed to what many consider the grandest oceanic collapse of all. The world's most productive water—in the simple terms of how much biomass is made there every day—is not off the coast of Peru, where anchoveta presently holds the title of world biggest fishery, but rather off the coast of Namibia. There, the Benguela Current Ecosystem produces more than twice as much phytoplankton as Peru's Humboldt system, and about nine times as much as the California Current system. The biomass of sardines alone in the Benguela Current was once about 25 million tons, or about a third of the entire world's current annual take from the sea.

But after sardines and then anchovies collapsed under enormous industrial fishing operations, so much plankton was left to sink unconsumed that the ecosystem tilted more and more frequently into a poisonous state that had always been a threat: a thick layer of detritus, rotting on the ocean floor, disgorges hydrogen sulfide gas, which fizzes to the surface, stripping out oxygen and killing more sealife along the way. So vigorous is the ocean's belching that even the sea breezes grow fetid and corrosive. Released from predation and competition, and favored by the low-oxygen conditions, jellyfish and bearded goby—a bizarre fish that survives hypoxia and eats sulfidic mud—have taken over, and now, it appears, locked in their advantage over sardines and anchovies. Unfortunately, humans can't eat all that much jellyfish, bearded goby, or sulfidic mud.

~~~

So what should be done? Or rather, now that we've realized that trophic cascades and ecological regime shifts can, in fact, happen in the ocean, what should we do differently? The case of coastal Nova Scotia gets at what a hard question this really is. The collapse of groundfish led to an expansion not just of herring, but also, somewhat later, of large shellfish, which adult cod had previously eaten. And in this case, the newly insurgent prey—shrimp and crab—have now exceeded the erstwhile value of groundfish they replaced. So after many fishermen became poor, some recovered, and some others have lately become almost rich. And now it's not even clear what the goal of management ought to be: Bring back the cod, and jeopardize the shrimp and crab? Or should we, instead, view our record of serial depredation—catastrophic though it's been for some—in a more positive light? After all, our history of failings has at least revealed to us various possible configurations the ecosystem can adopt, and such knowledge might—might—enable us to manage with ecological savvy, tilting the system in the very directions we desire, and thus maximizing its value.

As alluringly sophisticated as this prospect sounds, there are reasons to approach it warily. Our record in Management 101: Sardines is spotty at best, so it's not exactly clear why we ought to feel confident in Management 505: Advanced Oceanic Biomanipulation.  It was this very course, in fact, that led managers to break the Benguela. Shortly after the sardine population had suffered a severe decline, managers tried to make room for it to rebound by heavily fishing anchovy, the sardine's competitor. But as we know, what they facilitated was not the recovery of sardines, but rather the rise of jellies and bearded gobies.

A fundamental challenge, it seems, is that the systems we might try to manipulate are so complex and dynamic as to be largely unpredictable. With all those different species, each with its own idiosyncratic natural history, each somehow linked with so many others, it's awfully hard to be sure that pressing any given circle, and thus tugging certain threads, is going to have exactly the predicted effects. You might set out to support cod or crab, and end up bouncing something else altogether. After all, no one had much idea what bearded gobies could do until they overcame the Benguela.

Another challenge is that the instruments with which we press and tug on the web are awfully blunt: trawls, vast nets, mile-long lines with hooks dangling below. Such tools cannot be used to trim a single circle in the diagram; rather, they harrow whole neighborhoods. As a result, to get that annual 160 billion pounds of seafood we keep, we scoop out fully twice as much. So manipulating an oceanic ecosystem might be like doing cat's cradle tricks while wearing boxing gloves.

And we haven't given a thought to the ecological effects that are not depicted in our diagram. Remember that success story of restoration in Yellowstone? It turns out the wolves helped repair riverine woodlands not so much by killing deer as by terrifying them, and thus keeping them from lingering lazily riverside, browsing down their favorite herbage. What ecologists call "the landscape of fear" is now known to be important in seascapes, as well. And the implication is that we cannot stand-in, ecologically speaking, for the predatory fish we take out, even if we also catch the prey they would have eaten. Sophisticated as we may be in our understanding of the trophic web, we can't pull off a good impersonation of tuna.

For all these reasons, Management 505: Advanced Oceanic Biomanipulation is maybe a harder course than we'd like to enroll in. But unfortunately, we may have little choice in some cases—when things have gone desperately awry, for instance, as they have in the Benguela; or when an ecosystem is just now wobbling between different paths, and even conservative management—keeping the recent status quo—represents a momentous choice. Ironically, on the Scotian shelf, where the prospect of oceanic manipulation was brought to the fore by the stubborn collapse of cod, it is now being raised, once again, by the cod's belated and surprising recovery. Kenneth Frank has recently shown how one regime shift may eventually give way to another: The herring population, having gained ascendancy over its predators, became so abundant that it overshot its own food supply. Fluctuations of the population have ensued, and in the deeper dips, the cod may just recover—provided people aren't fishing for it. And so the top-predator, it seems, may soon reclaim its name.

That is, if we let it. And this raises what is, perhaps, the hardest challenge for a program of intentionally tilting ecosystems into arrangements that maximize value. As is often the case in economic arguments, "maximize value" is a phrase that sweeps an awful lot of complexity under a semi-technical rug. The really tough question is: value to whom? After all, cod fishermen and shrimp fishermen are not the same parties. And you cannot decide what to do simply by summing the total price fetched or profit garnered by a season's shrimp and comparing it with that of cod, because the different kinds of fishing entail different sorts of workforce, different distributions of wealth in the community, different ways of life. Deciding to manage for groundfish or shellfish is effectively to make choices in all of these arenas at once. And yet, the dynamics of the ecosystem dictate that, like it or not, a decision will be made.

~~~

In Bahía de los Ángeles, too, I have glimpsed what complications may hide behind pesos and pounds, the simpler measures of a fishery's value. The Humboldt squid—that creature my students hoisted from the deep—supports what is, by weight, the Gulf of California's largest fishery, amounting to about a quarter of a billion pounds per year. In view of such scale, it is surprising to realize that, prior to the late 1970s, no one in the northern gulf ever fished for squid, because there were hardly any there. What fishermen pursued instead were large fish, such as tunas and jacks. But then, in yet another variation on the ecological theme, the tunas and jacks were fished down, and their rarity helped open the way for squid. And since squid are voracious predators of just about everything, it is likely that their consumption of young tunas and jacks has helped maintain the new regime.

As in coastal Canada, however, we must at least ask: was the shift, perhaps, a boon? A quarter of a billion pounds is a huge take, even compared to the tuna and jack of yore. And yet, the deeper you look into the value of the largest fishery in the Gulf, the less favorably the new regime seems to compare. To start, Humboldt squid is cheap: a fisherman sells it for about five cents per pound. By comparison, tuna and jack are precious, fetching a few dollars per pound. And it's instructive to cut still deeper into such monetary measures. A fisherman casts aside a squid's arms, tentacles, and head—everything but the mantle, that tubular torso of muscle. So if you calculate what he gets for every pound pulled from the water, it works out to be more like two or three cents. And though this quantity is irrelevant at the market, it is nonetheless meaningful as a measure of hard labor at sea.

For squid, that labor is done at night, when the animals rise from the depths to feed nearer the surface. This makes the undertaking more dangerous, not to mention hard on fishermen and their families. And finally, it's important to remember another way in which average catch and price do not tell the whole story. The predatory fish that have suffered under the squid’s recent dominance make up a diverse assemblage of at least six different species. Diversity in an ecosystem often confers the same benefit as it does in a stock portfolio: when conditions are bad for one part, they are good for another, and thus the system as a whole is less prone to spikes and crashes. And since fishermen and their communities are not the sort of investors who can wait out bad times, volatility is as important as average return.

So, no, I do not believe the new regime is better for fishermen. But of course, there are more and less audacious ways to foment revolution and achieve regime shift. To start, you could halt catches of predatory fish; that hasn't really been tried, and, judging from the experience in Canada, it might let the fish rebound whenever the squid happens to have a bad year. More brazenly, you could intentionally overfish Humboldt squid, driving it into decline. Then again, that advice is offered with the caveat that you might soon find yourself up to your neck in jellyfish.

~~~

Charles Darwin toppled Homo sapiens from the apex of the Great Chain of Being, depositing him among all the other species in the tree of life. It was, of course, a humbling demotion: man was not so unique and important as he'd presumed. Among the defenders of Darwin's ideas, Thomas Huxley was perhaps the most fervent and determined, for which he earned the nickname "Darwin's bulldog." In 1883, Huxley was invited to give the inaugural address at the International Fisheries Exhibition, in London. He took the opportunity to weigh in on a debate that had lately been heating up between artisanal fishermen and newly emerging, industrial-scale operations. The central question in this debate was this: Should the legislature of the United Kingdom regulate fishing, specifically when and where certain kinds of gear may be used?

Huxley got the answer wrong. Tragically wrong. "I believe," he said, "that the cod fishery, the herring fishery, the pilchard fishery, the mackerel fishery, and probably all the great sea fisheries, are inexhaustible; that is to say, that nothing we do seriously affects the number of the fish."

Even as he spoke, several North Atlantic fisheries were in steep decline. But, as would still be the case more than a century later, it seemed more likely to many scientists that the ocean's own mechanisms, and not the work of humans, had to be the cause. Already the two kinds of explanation—those focused on the forces of the ocean below, versus those suspicious of the fishing boats above—were confounding each other. But the fact that it was Huxley, Darwin's bulldog, who so clearly stated the thesis of inexhaustible seas makes one wonder if there wasn't another reason, besides the confounding nature of oceanographic and ecological theories, that it took so long for scientists finally to grasp that top-down control can in fact happen in the ocean. Perhaps that idea has seemed at odds with the basic Darwinian notion that we are but one twig among many—not atop Nature, but within it. In other words, having toppled man from the Great Chain, it was difficult for Huxley and others after him to see that Homo sapiens was indeed at the top of every food chain. Compared with the ocean's vast shoals and voracious predators, Huxley argued in his speech, fishermen are minute in stature, trivial in their impacts. But could it be that such humility with respect to the rest of the natural world is sometimes tragically misplaced?

Perhaps so, especially if it causes us, again and again, to be taken unawares by the magnitude of our own actions: Top-down control can happen in ponds, scientists thought at first, but surely not in the open ocean; but then we converted the greatest of oceanic ecosystems—the Benguela Current—into our own stinking pond. Regime shifts occur, oceanographers found, when the earth's largest system of oceanic circulation exhibit massive rerouting; but then we proved ourselves a force commensurate with Oceanus himself. Top-down control cannot happen in the ocean, an important argument went, because of the high biodiversity on each floor of the food web; but then we cleared out whole stories all at once, and regime shifts ensued.

My students' fishing tale has always struck me, I suppose, because it is a kind of metonymic enactment: little fish is eaten by big fish; big fish is caught by humans; and finally, big fish is replaced by undesirable species—but not without the help of our fishing line. The Canadian shelf and the Benguela current; the North Sea and the Sea of Cortez—they are all, in a way, theatres of a single, overarching regime shift. And the vital question now is whether the species in power will govern wisely. What happens if we do not is depicted, I think, in the image of a ten-ton trawler, pulling itself over, and dumping the crew in among the jellyfish.

© Aaron Hirsh. All rights reserved.

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