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are nature's chief way of transporting sediment from shallow to deep
water, and the resulting deposits ('turbidites') are common among the
Earth's strata (on the steep slopes, turbidity currents have carved out
the submarine canyon systems too). Hence, as a side-effect of trawl-
ing, humans are now mimicking one of nature's patterns. More dis-
tantly, there are layers of far-travelled fine mud that have settled. It is
a new sedimentary system that is being added to every day, as the
world's trawling fleets set out to work.
Muddy and sandy sea floors recover, after a fashion. There have
even been claims that the ploughing of the sea floor is beneficial. Cer-
tainly, there are winners as well as losers: those species most resilient
to physical disturbance, and to the choking effects of increased tur-
bidity in the water, are ready to take advantage of the discomfiture of
their more delicate neighbours.
Among the worst losers of all are complex, slow-growing submarine
ecosystems. The tops of many deeply sunken mountains are—or used
to be—often crowned with a delicate tracery of deep-water coral colo-
nies that provide shelter for a variety of animals. In recent decades, the
trawler fleets, in search of their particular prey, have simply smashed
through the delicate coral growths, effectively reducing parts of the sys-
tem to a mass of rubble. There is still an ecosystem of sorts among the
dead and broken coral fragments, but one of generalist survivors—a far
cry from the biological richness of the original deep-sea reefs. There are
now controls in place to try to protect the remaining deep-water coral
stands. How effective they will be remains to be seen.
Changing the Balance
Has there been anything in the Earth's past quite like the human-
driven fisheries project? As an example of predation by one species—
amazingly, a terrestrial one—on the ecosystems of both the open
ocean (including surface, mid, and now increasingly deep waters) and
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