Deep Trouble

Adaptations to deepwater living make the fishes of the deep sea particularly vulnerable to overfishing.

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trawling
Bottom-trawling gear, depicted here schematically, is dragged across the seafloor. Fish in its path are herded into the net, which can span the area of several football fields. A chain at the bottom of the net connects two five-ton steel plates, which keep the net open. The gear can weigh fifteen tons and disturbs or destroys any features in its path. (Mieke Roth, NowHow Scientific and Technical Visualisations)
trawling
A deepsea chimaera (a distant relative of sharks) with a rockling in the background (Chevron Canada Limited and the SERPENT Project)
trawling
A deepwater skate glides along with a grenadier beneath it. (Chevron Canada Limited and the SERPENT Project)
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.


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