The deck was covered with fish. I’d never seen anything like it. There were long, slender eels, black sharks, pale rays, silvery grenadiers with long, pointy tails, and great black things with huge, dark eyes. We’d needed the biggest winch on our research vessel to haul them up from the bottom of the North Atlantic, some 5,000 feet below the surface and a hundred miles east of New York City. My colleagues and I waded into the catch and began sorting the various species into piles, marveling at their extraordinary forms.
I was a young fish biologist at the time, part of a team studying the distribution of fishes elsewhere in the deep sea: not at the bottom but in the midwaters, a part of the water column above the seafloor. We regularly trawled the midwaters at various depths down to 3,500 feet. After towing a net for as long as three hours, we’d come up with a sample at times no bigger than a teacupful—or, if we were lucky, a small bucketful—of sardine-size creatures. But a break in that routine had given me a chance to see what lives even deeper, and so we broke out the bottom-trawl net. Even as the ship’s crane swung the bag, or “cod end” of the net, aboard, I could see that bottom samples were entirely different. The net was bulging, and when the knot cinching it shut was undone, a great swirl of mud and sea creatures had spilled onto the deck.
And the fishes! Not a cup or a bucket of small fry, but more like half a ton of strange and wonderfully big fishes. I was hooked. That first bottom trawl, forty years ago, launched a lifelong career in research and teaching about the fishes that live at the bottom of the ocean.
My colleagues and I have learned that those bottom-dwelling animals typically grow slowly, delay reproduction, and live long lives—adaptations to making a go of it in the cold, dark, nutrient-poor waters of the deep-sea floor. But those same attributes make the fishes particularly vulnerable to a new stress: deep-sea fishing. As populations of shallow-water fishes have crashed, the global demand for seafood has led to rapid overfishing of the bottom, along with the habitat destruction that bottom-trawling wreaks. We estimate that more than 20 percent of the northwest Atlantic’s deep-sea fish species have declined so seriously that they should be considered for threatened or endangered status. And the same thing is happening the world over: deep-sea fishes everywhere—from Greenland halibut near the Arctic Circle to Chilean sea bass off Antarctica—are being hunted to the verge of extinction. If I were to return to that spot in the North Atlantic where I made my first bottom trawl, the deck would no longer be covered with fishes. I’d be lucky to catch a bucketful.
The deep sea does not begin at the beach; it encompasses the waters from surface to seafloor that lie beyond the continental shelf. Shallow coastal waters overlie the shelf, which can extend a hundred miles or so from shore. There, at the true edge of the continent, where the water is about 600 feet deep, the topography steepens. The seafloor plunges some 6,000 feet down the continental slope, then declines more gently down the continental rise and onto the abyssal plain. The average depth of the plain is 13,000 feet, but it is interrupted by trenches as deep as 30,000 feet, or by mountainous ridges and volcanic seamounts, some of which reach the surface to form island chains, such as Hawai’i [see illustration left].
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Early ocean explorers thought conditions in the deep sea were too harsh to support life. In fact, though, the deep sea, both in its midwaters and on its continental slopes and rises, is populated by an extremely rich and widespread fish fauna. (The abyssal plain itself, however, is relatively devoid of fish.)
The deep-sea midwaters are home to an unusual cast of characters: lanternfishes with glowing lights, silver hatchetfishes with telescopic eyes, and viperfishes with tremendous fangs, among many others. But midwater fishes are sea monsters in appearance only: most are no longer than a foot. Because of their diminutive size and relatively low density, no extensive deep-sea midwater fishery has yet developed.
The continental slopes are another story. At depths between 600 and 6,000 feet, the slopes are where the fishing happens. Animals living there are bigger and more abundant than in the midwaters of equal depth, largely because the bottom provides both structure and a collection place for food particles falling from the productive surface waters.
Yet despite the increasingly heavy commercial fishing there, much remains unknown about continental slopes. Worldwide, just a fraction of 1 percent of their total area has been explored, and investigators have only recently begun to appreciate the complexity of slope habitats. In part, that’s because most of the slopes appear to be featureless expanses of dull mud. Only a few areas, such as the hot vents of tectonically active ridges and trenches, were acknowledged as dynamic and structured ecosystems. But it turns out that even the mud is home to thriving populations of crustaceans, sea stars, urchins, worms, and myriad other creatures. Recently, even deep-sea coral beds have been discovered to be widespread on the world’s continental slopes. They play host to a highly diverse and little-known fauna, and it is likely that their tangled structure provides protective cover to juvenile fishes.
The fishes of the continental slope display numerous adaptations to deepwater living, which include cold tolerance; longevity; and enhanced vision, hearing, and sound production for making their way in darkness. Certain species, such as deepwater rays, rockfishes, and eelpouts, bear live young or build nests to give their young a head start in a tough environment. Many slope dwellers are relatively large—between one and three feet long—which enables them to forage over broad areas. Many also live in schools. Both their size and schooling behavior have made certain species attractive targets of fisheries—which has in turn brought about the fishes’ undoing.
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The main reason for their vulnerability is their slow growth rate, a fact of life at depth. Light does not penetrate to the continental slope, so no photosynthesis takes place there, and there is no in situ food production. Virtually all the energy for the slope’s food chain must be imported. Most comes in as debris raining from above—from dead phytoplankton to dead whales. Even so, there isn’t much. Throughout the deep sea the available food declines quickly with depth, increasing somewhat on the seafloor itself.
As a result, the abundance, biomass, and metabolic rates of organisms also decline. With a low metabolic rate, a fish takes longer to grow to maturity: a cod on the shallow continental shelf matures in four to seven years, whereas a grenadier on the continental slope may take eighteen years. By the time many deepwater fishes are big enough to be worth catching, they are older than your grandmother: the fillet of orange roughy you order at a restaurant could easily come from a fish born before the invention of the automobile.
Thus populations turn over quite slowly. A fishery naturally targets the largest individuals, and so can quickly wipe out most of a population’s mature, reproductive fish, which can take decades to replenish. Add to that the possibility that some slope fishes might only spawn once at the end of their long lives, and you have a recipe for extinction.
Except for a few special cases, deep-sea fisheries are all of recent vintage. In the early 1970s Soviet fishermen became the first to systematically locate and exploit continental-slope fishes. But despite glowing accounts of the tastiness of the fishes—blue hake, deepwater sharks, grenadiers, and slickheads, among others—a strong international market never developed. The fishery instead supplied immense quantities of low-quality product to the former Eastern Bloc, where cheap protein was in demand. State-sponsored fleets from the Soviet Union—and later, from its former republics—aggressively fished the northwest Atlantic and various other regions into the 1990s; some are still active today.
Worldwide, the expansion to the deep sea stems directly from the severe depletion of shallow-water fisheries. In the northwest Atlantic, for instance, the collapse of cod in the early 1990s became one of the most dramatic fish-stock crashes of all time. But the industry found a substitute in the deepwater Greenland halibut. Predictably, that species is now in trouble throughout the Atlantic. Elsewhere, deep-sea fisheries have developed for numerous species, including icefish in the waters off Antarctica, Patagonian toothfish off Argentina and Chile, hoki off Australia and New Zealand, black oreos off New Zealand, thornyheads near Pacific seamounts, and giant rattails in the northwest Pacific.
The deep-sea orange-roughy fishery near Australia is a prime example. It was developed to satisfy the middle-American market for a bland, white fish. Even the name was picked through careful supermarket research (its original moniker, the slimehead, sounded far less appealing). And when that fishery began its inevitable decline, the industry moved on to another deep-sea species, the Patagonian toothfish. It was renamed the Chilean sea bass, even though it is neither a bass nor exclusively Chilean. It, too, has now suffered sharp declines.
The bottom-trawling gear for deepwater fishing is basically the same as the gear deployed in shallow waters, but on an enormous scale. Factory ships longer than 300 feet can hold 1,000 tons of fish and stay at sea for 300 days a year. Massive winches and cables are needed to reach the slope bottom, ten times deeper than the continental shelf. The net itself is woven from heavy polypropylene line and can span the area of several football fields [see illustration left]. A pair of steel plates called doors, weighing as much as five tons each and connected to the net with heavy cables, spread the net open under water. The doors and cables scrape along the ocean floor and herd fish into the net—as much as twenty tons in each haul. The entire rig can weigh fifteen tons, and is dragged across the bottom for several hours at a clip of four miles an hour or more. Little more than finely ground rubble remains on the seafloor in its wake.
In theory, a fishery should be managed sustainably, taking no more each year than what reproduction replaces. Thus the size of the take is determined by numerical models that can estimate future populations. Accurate estimates depend on accurate information about a species’ age at maturity and its growth rate. Those numbers depend, in turn, on survey data on abundance and body size—a proxy for age.
Yet none of those data existed reliably for deep-sea fishes as their fisheries developed. Managers set catch quotas essentially by guesswork, relying on their knowledge of shallow-water species. They took no account of the far slower turnover rates in a typical population of deep-sea fishes. And even when fisheries could not catch enough fish to meet their quotas, as was the case with the roundnose grenadier for more than twenty years, the quotas were not decreased.
Unfortunately, circumstances today have not much changed. Most deep-sea fisheries, as in decades past, are little more than mining operations that run until they exhaust their target populations and collapse. Then they move on to another species.
[pagebreak][media:node/1169 horizontal medium right caption]In 1987 my students and I began to study the ecology of fisheries. As continental-shelf stocks declined and fisheries moved into deeper water, we followed them out to sea. In 2002 we turned our attention seriously to understanding how fishing had affected deep-sea fishes. We began by examining the roundnose grenadier and the roughhead grenadier, or onion-eye, using scientific survey data assembled annually by the Canadian government. Soviet trawlers and others had been fishing the two species off Canada since 1970, but catches had plummeted in recent years. Sure enough, we discovered that their populations had declined by as much as 99 percent since 1978, precipitously enough to qualify them for endangered status.
Decline rates are one thing, but the big question both ecologists and fishery managers ask is, how long will species take to recover from exploitation? There is a widespread assumption that fish populations can still recover even after they have declined by 95 percent or more. But that rests on hope as much as on any solid evidence. And even taking an optimistic view, most species—even fast-growing continental-shelf species—will probably need decades, not years, to make a full recovery.
For the roundnose and roughhead grenadiers, even the minimal information required to make predictions about recovery times was not gathered until two decades after the fishery began. By that time, the fishery had collapsed, and populations of both species could qualify for endangered status. My colleagues and I calculated the grenadiers’ recovery times on the basis of those data; they range from decades to more than a century, assuming no more fishing—not a surprising result, given those fishes’ slow growth, delayed maturity, and long lives.
We have now extended our research on grenadiers to forty species of continental-slope fishes in the northwest Atlantic. (There are about sixty species in all, but we are limited to those for which there are enough data to determine changes in abundance.) It is worth noting that ours is the world’s first ecosystem-wide assessment of the effects of fishing in the deep sea—the subject is so little researched. Eight of the forty species, we discovered, have declined so precipitously that they could be considered threatened or endangered. Another ten species have also declined, though not as much.
When we began the research, we had expected to find that large, free-swimming fishes, which are most susceptible to capture by bottom trawls, had suffered the most marked declines. But that was not the case. Rather, the declines were greatest among small species, including the Arctic eelpout, Scotian snailfish, and wolf eelpout. Those species live right on the bottom, often hiding among rocks. We suspect that habitat destruction by trawling, not entrapment in nets, played the leading role in their decline. And though that decline is worrisome enough in its own right, it may portend habitat destruction on a scale that could have repercussions throughout the ecosystem.
The fragile deepwater corals that create desirable habitat for many fish species are no match for the heavy trawls, either. Recent studies have shown that the corals grow extremely slowly: a coral growing on the bow of the Titanic, photographed not long ago by a Russian submersible, is hardly two inches tall. Severely damaged deep-sea coral banks will probably take millennia to recover fully. So, in addition to the direct effect of the nets on fish populations, their unintended effect on habitats is so completely and enduringly destructive that the populations may never recover. The species are simply unlikely to survive long enough for their habitats to reestablish themselves.
Fortunately, governments are taking note of the scientific findings—both my own and those of others. Last year a resolution to ban trawling in international waters was debated in the UN General Assembly. It failed, but just barely: UN resolutions require unanimity, and a handful of nations—Iceland the most prominent among them—did not agree with the rest of the world.
Still, many countries are taking unilateral action to limit deep-sea trawling within their own exclusive economic zones (EEZs), the 200-mile-wide strip of ocean that lies just off a nation’s shores. Virtually the entire Mediterranean Sea is now protected; Australia, the Azores, New Zealand, and the United States have set aside large regions where such fishing is off limits, as it is in the waters off Antarctica. Trawling bans are now in place over more than 4 million square miles.
That, of course, is a small fraction of the entire world ocean—the Pacific alone is 65 million square miles—and even then the protected regions are hard to patrol. Enforcement is all but impossible in remote areas such as Antarctica. And illegal trawling is not the only threat: poaching, misreporting of catch and bycatch, and various other destructive practices are all too common. The prospects for conservation seem dim. Indeed, fishermen are already turning away from depleted deepwater fish stocks and casting their nets and traps further down the food chain. Deepwater shrimp and crabs have become the latest targets, a familiar story with a predictable end.
Fishing-industry representatives who resist efforts to regulate deep-sea fisheries argue that too little is known to make rational decisions. Declining fish populations, they maintain, probably just reflect natural cycles. But marine biologists nowadays know more than enough about deep-sea ecology and the biology of deepwater fishes to recommend good choices.
Fisheries must balance human needs with the imperatives of the ocean. For the deep sea, in particular, short-term economics must come into alignment with long-term biology—surely a predicament whose resolution is not beyond human ingenuity. We must all learn to live with fishing practices adapted to the laws of nature in the deep sea, just as the fish living there have adapted. Evolution sets the pace of life in accord with physical conditions, and in the deep sea that pace is slow. The pace of our fishing there would do well to match it.