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were once a yard long. Plaice were the size of road atlases, turbot like
tabletops. The specimens we see on the fishmonger's slab are, for the
most part, youngsters, caught before they were able to reach even a
tenth of their maximum weight.
Genetic profiling of the great whales suggests that their popula-
tions, before whaling began, were higher than biologists had assumed.
The larger the original population, the greater the variation within
that which remains. An analysis of genetic data in the journal Science
suggests that the North Atlantic alone supported around 265,000 minke
whales, 360,000 fin whales and 240,000 humpbacks. 10 Today the
minke whales, after a severe population decline, have recovered to
149,000, the fins to 56,000 and the humpbacks to 10,000. The whales
once visited all the seas of the region; by the eleventh century they
were being hunted in both the English Channel and the North Sea. 11
Just as on land, the ecology of the sea is more complex than scien-
tists once assumed. The trophic cascades now being discovered in the
oceans are, if anything, even more remarkable than those of the ter-
restrial ecosystem. Fishermen and many fisheries scientists, for
example, have long assumed that if whales are removed from the
southern oceans, the volume of their prey - mostly fish and krill - will
rise. This argument has been used by the Japanese government to jus-
tify its continuing slaughter of these beasts. 12
But recent work suggests that reducing the population of whales
might have had the opposite effect. As whale numbers have declined,
so have the krill: 13 to just one-ifth of their volume before the 1980s. 14
Their collapse, until recently, mystified observers. It now seems that
the whales perform an essential role in keeping nutrients in the sur-
face waters. If undisturbed, the plant plankton at the bottom of the
foodchain sinks out of sight, beyond the photic zone (the waters in
which the light is strong enough to permit plants to grow). The nutri-
ents it contains sink with it, becoming unavailable to most lifeforms.
The surface waters rapidly become depleted of essential minerals,
especially iron, whose scarcity limits growth. In the summer, when
plant plankton is reproducing fastest, the wind and waves drop,
allowing it to sink more rapidly. The same applies to the faeces of the
animals that eat it.
Even today, a study in the journal Nature calculates, the mixing
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