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In A Perfect Ocean
The State of the World's Ocean Series
By Daniel Pauly
ISLAND PRESSCopyright © 2002 Island Press
All rights reserved.
A Brief History of the North Atlantic and its Resources
Unmarked and trackless though it may seem to us, the surface of the ocean is divided into definite zones, and the pattern of the surface water controls the distribution of its life. Rachel Carson, The Sea Around Us, 1961.
... the number of the cod seems to equal that of the grains of sand ... These are true mines, which are more valuable, and require much less expense than those of Peru and Mexico. Charlevoix, 1720s.
The Atlantic Ocean as we know it is only about 20 million years old, geologically quite young, and its breadth is still increasing by a few centimeters each year. The Ocean developed from the splitting up of Pangaea, the only land mass, or continent, in pre-Jurassic times. At that time a single giant ocean, Panthalassa, surrounded the land. Pangaea began to break into northern and southern segments about 200 million years ago, and a fissure that is now the mid-ocean ridge began to divide the American continent from what became Europe and Africa, creating the Atlantic Ocean between the two landmasses (Figure 1).
Along with a slow but continuing expansion, there are environmental processes operating in the North Atlantic Ocean at different time scales. Long-term processes such as climate change include the ice ages, the last of which occurred roughly 15,000 years ago, and caused northern North America and northern Europe to be covered under one kilometer (one-half mile!) of ice. This greatly reduced sea levels, to the extent that shelf areas such as the Georges Bank off New England and the North Sea were exposed, covered by extensive forests. Medium-term processes last for periods from a few weeks to a decade, and include the North Atlantic Oscillation, which affects the weather in North America and Europe, and can be presumed to affect, as well, the marine "weather" to which fish are exposed, and which, jointly with parental population size, determines their reproductive success.
Finally, short-term processes occur on daily, seasonal, or annual cycles, including tides, which mix nutrient-depleted surface waters with subsurface water, and seasonal upwelling, where wind-driven current parallel to coastlines forces deep water toward the surface. These processes are important, as it is only through mixing of the nutrient-depleted surface waters with nutrient-rich subsurface or deeper water that the nutrients (nitrogen, phosphorus, etc.), which are required for the growth of the algae at the base of marine food webs, are renewed.
The major currents which, from a satellite's-eye view, describe huge arcs, swirls and eddies across thousands of kilometers, define the oceanic ecosystems of the North Atlantic, while its bottom features define the ecosystems on shelves down to depths of 200 m (600 ft). The major surface current systems in the North Atlantic travel broadly clockwise; those in the southern hemisphere move counter clockwise. This results in very different climates on the east and west sides of the Ocean—the relatively warm water of the Gulf Stream flows the whole year north past the British Isles, while the sea off Labrador at the same latitude is frozen for half the year.
The world's oceans are divided into 4 biomes: the Polar biome, containing polar and subpolar oceans, which make up only about 6% of the total; the Westerlies biome, containing the temperate and subtropical areas of the oceans, about 54%; the Tradewinds biome, corresponding roughly to tropical sea areas, 33%; and the Coastal Boundary biome, comprising all the shelf waters adjacent to land masses, which constitute the remaining 7% of the total ocean area. Globally, these biomes are further subdivided into 57 dynamic biogeochemical provinces—"dynamic" because their borders vary seasonally, and "biogeochemical" because the living organisms ("bio-") therein respond to local ("geo-") processes that determine delivery of nutrients ("chemicals") to the sunlit surface waters, and hence determine the intensity and duration of primary production. The North Atlantic contains 18 of these 57 provinces.
Most of the North Atlantic's provinces are in the open ocean, where the surface waters are infrequently enriched with nutrients from deeper waters. This leads to a low production by planktonic algae, and a generally impoverished environment, similar to terrestrial deserts, inhabited only by large fish such as tuna, which are capable of quickly crossing their large unproductive expenses to find scattered patches of high production "oases."
In contrast, the provinces of the coastal biome, an area of strong water mixing, support high levels of primary production, and it is from the ecosystems embedded in these provinces, e.g. Georges Bank or the North Sea, that most North Atlantic fisheries catches are, or were, taken. These coastal areas, which extend out to the seaward boundary of continental shelves and the outer margins of ocean current systems, can be divided up into "large marine ecosystems" (LMEs), regions of ocean space with distinct bathymetry (the oceanographic equivalent of topography) and productivity patterns. Fourteen LMEs cover the coastline boundaries of the North Atlantic. Fortunately, there is great congruence between the LMEs and coastal biogeochemical provinces, enabling data from both sources to be jointly mapped in a rigorous manner using geographical information systems (Figure 2).
Within each of these larger ecological units, or ecosystems, the numbers and types of fish, the fish "communities," are unique or at least distinctly different from those in other ecosystems. (Note that the term "fish" is used in this book to mean organisms fished: all the animals caught by humans, including fish per se, i.e., "fin fish", shellfish such as crabs and shrimp, mollusks such as oysters, clams, conches and squid, and other invertebrates like sea urchins. Seaweeds and other algae, although sometimes included among "fish," are not covered here.)
The communities of each ecosystem are interrelated through unique and complex food webs. The animals prey on each other; some marine mammals and sharks prey on large fish such as cod and mackerels; the large fish prey on smaller fish such as herrings and anchovies; and these small fish prey generally on animals among the plankton—composed of tiny less-mobile animals and plants (algae). Other small fish and the animal plankton (zooplankton) eat the plant plankton (phytoplankton), which constitute the bottom of the web. These microscopic phytoplankton use the energy in sunlight in a process called primary production to produce new matter in the form of themselves, as plants do on land. As on land, the sun provides the energy that drives the system. Humans earlier impacted marine food webs at the level of marine mammals and sharks, i.e., as top predators, but the versatility that made our species so successful on land has proven equally effective in the oceans, and we are now attacking all parts of marine food webs, right down to the plankton.
Thus, when fishers extract fish from an area of the sea, they affect the properties—the balance or dynamics, and even the physical structure—of the ecosystem in that area to some extent, in some cases much like the changes in terrestrial ecosystems when clearing a forest for farming. Therefore, fish captured for human use needs to be seen in its ecosystem perspective if we are to assess the real impact of removing the fish. Fisheries science has so far been based mainly on the interactions between fish and fishers, without much attention to the fact that humans (meaning here humanity as a whole, for the fishers are acting on behalf of all fish-eaters worldwide) represent but one predator, added to those naturally occurring in each ecosystem. One of the results, as we will show, is that ecosystem impacts of fishing were not noticed until they had already had their impact on the fisheries.
Past Abundance in the North Atlantic
The earliest accounts that we have of fish populations in the North Atlantic make it clear that both sides of the ocean once contained an abundance of fish—not to speak of marine mammals, seabirds and turtles—that we may find now almost unimaginable. It is uncomfortable in a way to absorb the fact that the past oceans were so different. Perhaps for this reason, many have doubted the veracity of the historical record. But in fact, the hard paleoecological evidence corroborates these accounts, and careful analysis paints a fairly unambiguous portrait. Past oceans were so well populated with fish and other marine life that the tales of old fishers about their "good old days"—that we don't believe as a matter of principle—were more than likely true. Even more discomforting, their forebears would have been saying the same thing, and they would have been correct, too.
On the eastern side of the North Atlantic, archeological evidence going back several thousand years shows that prehistoric hunters in other areas caught a wider variety of larger fish than now. In parts of northern Asia (now the Russian Federation), the salmon and sturgeon harvested were bigger, and there were 40% more species than found there now. Likewise, remains in ancient middens in the Mediterranean contain more kinds of fish and larger individuals than occur in that sea now.
Since at least medieval times, fish were vital for domestic consumption and trade in many countries. It was said a vast army of herrings poured down from the north each year and created the wealth and balance of power among the major European nations. Cod was the staple food on everyone's table, rich or poor, and its relatively low price suggests that it was abundant, hence easy to catch. Yet, in spite of the abundance of fish in their coastal waters, particularly giant cod, halibut, and turbot in the North Sea, the first Europeans to reach the shores of the northwestern Atlantic were amazed by what they saw.
By all accounts, the western side of the North Atlantic was teeming with marine life. Our knowledge of those marine ecosystems comes from "snapshots" from early visitors from the eastern side of the ocean, which make present day reminiscences about the good old days of fishing pale in comparison. Those early navigators, fishers and biographers report that one didn't need a hook, just a basket, to catch big cod, while the ships would bump into whales lazing on the surface, so plentiful were they. The pilgrims on the Mayflower were surrounded by whales when they arrived at Cape Cod. Chesapeake Bay was alive with whales, and settlers discovered it was only one of many bays along the northeast American continent populated by large numbers of the creatures. They were regularly reported to have hindered the movement of vessels. It certainly stretches the imagination, looking at the empty ocean now, to visualize the frustration of these early travelers caught in the whale traffic of the sixteenth and seventeenth centuries. But there was adequate proof of these reports in the massive influx from Europe of fishing and whaling vessels by the hundreds whose crews, with government support, for decades fought relentless if unofficial wars to gain control of the new fishing grounds.
Cod was but one of the many species that made up the wondrous bounty of the northwestern Atlantic. Author Farley Mowat's Sea of Slaughter quotes many on-the-spot "snapshots" of the abundance of different kinds of marine life there by visitors in the 1500s and 1600s. Among them were turtles in "inestimable numbers," "an infinite number of them all over the sea"; "harbours writhing with the silver-sided splashing of the stripers" (striped bass); huge salmon in "prodigious quantities"; sturgeons "in great plenty" and "so numerous that it is hazardous for Canoes"; "the greatest multitude of lobsters ever heard of" in the Gulf of St. Lawrence; and a great abundance of oysters and mussels.
Taken in total and even allowing for some enthusiastic exaggeration, the northwestern Atlantic must have been almost like another planet, so alien was it from the previous experience of all these travelers. And it should be noted that in those days, the opposite side of the Atlantic, whence they came, was by no means empty of fish.
Historical reports from the seventeenth century include accounts of divers using diving bells to explore the ocean floor. What might they have seen?
A walk down from the shore into a bay such as the Chesapeake, trailing hoses that supply air pumped by bellows, would have revealed an abundant and somewhat fantastic seascape. A few meters down, fully underwater, there are odd-shaped flat rocks, up to a foot long, lying one on top of the other in vast piles. These are oysters, their shells barely open, gently filtering plankton from the water. In more sheltered places, great clumps of mussels do the same thing. There are so many of these filter-feeders, not to mention dozens of clams buried under every square foot in some sandy or muddy shallows with siphons reaching up to strain the water, that they can keep the bay's waters clear even during the spring blooms of plant plankton. In fact, it is estimated that prior to European settlement, the bay's oysters filtered the entire volume of Chesapeake Bay waters once every three days.
Further North, in places like Long Island Sound, lurking under rocks and crawling around the bottom, were humongous lobsters of 16 to 25 pounds each. They could easily be netted by the hundreds here, and each could feed several persons. There are plenty of fish sheltering amongst fronds of brown algae that reach upward from the rocks, while sea urchins graze on the fronds. The algae grow fast in these clear waters, fast enough to keep up with the consumption of the urchins.
Elsewhere, there is a wilderness of small animals on or near the bottom, moving around or clinging to rocky outcrops. There are crabs, shrimps, sponges, snails, starfish, squid and small fish in profusion. At these depths many of the fish are probably the young of large fish like cod, haddock, hake and pollock. They are protected from predators—including larger members of their own species—by the rich bottom structure, notably sponges and sea fans, providing hiding places from which they dart to catch drifting food morsels.
Depending on the season, there would be huge groups of sturgeon on their way to a river, each measuring up to an astounding 18 feet, bigger than nearly all the sharks and rivaling many marine mammals. Salmon, ranging up to six feet long, swim in massive, shimmering spawning schools as well. Hordes of striped bass, with some individuals weighing 50 pounds or more, patrol near the shore for schools of menhaden; they, too, will travel upriver to spawn. Huge schools of menhaden, capelin, herring, smelts, or other species swim in close formation, almost as one, for protection, eating plankton and becoming food for the larger species. Sometimes loggerhead turtles swim at the surface by the thousand. Abundant leatherback turtles—six feet long, weighing maybe half a ton—troll for slow-moving jellyfish.
Further offshore the big fish cruise languidly about. Here there are cod, three to six feet long, browsing along the bottom, stopping to crunch a snail or sea urchin or swallow a slow squid or small fish. They are gliding by in every direction, and among them are numbers of tomcod and haddock.
A huge shadow precedes a baleen whale sounding, and another; they fill the whole field of view, underwater and on the surface. The eerie sounds of clicking or groaning are all around as they communicate with each other.
Sudden flashes above are bluefin tuna chasing small fish toward the surface. The tuna are between six and twelve feet long and in a few seconds they are gone. But flashes of other groups pass time and time again, along with the occasional sailfish. What impresses most is the sheer numbers of large fish. No wonder they could be netted or hooked by the thousand, by the million.
And they were.
Excerpted from In A Perfect Ocean by Daniel Pauly. Copyright © 2002 Island Press. Excerpted by permission of ISLAND PRESS.
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