91av

CENTURIES of overfishing have inflicted more damage on coastal marine
ecosystems than the modern ills of pollution and climate change.

The pre-industrial harvesting of sea creatures such as turtles, otters and
oysters eventually triggered the collapse of many ecosystems, says an
international team of scientists. But the havoc wreaked by early societies has
been largely overlooked. Besides plundering the ocean, many palaeontologists
blame humans for wiping out the giant animals that roamed the Americas until
about 10,000 years ago.

Karen Bjorndal of the University of Florida in Gainesville and other team
members combed through archaeological and historical data to estimate the extent
of pre-industrial fishing.

“We thought the real threat to the green turtle in the Caribbean came with
the arrival of Europeans,” says Bjorndal. Yet refuse tips in use soon after
American Indians reached the Bahamas between AD 600 and 800 are full of turtle
bones.

The Indians settled near nesting beaches, where, she says, turtles were “a
great source of food” for three to six months of the year. Europeans exacted a
further toll. Records show that by the 18th century, colonists could no longer
catch enough turtles in North Carolina, and had to import them from the Bahamas,
says Charles Peterson of the University of North Carolina. Today, Bjorndal
estimates that green turtle numbers are just 5 to 10 per cent of their original
level.

Green turtles were the first of several herbivores people hunted. They turned
to parrot fish and sea cows later, leaving sea urchins as the last animals
keeping seagrass and marine algae in check. When disease devastated the urchins
about 15 years ago, algal blooms started to choke coral reefs. “Ecologists
thought the problem was that the sea urchins died off, but in reality the
problem started when the turtles were killed off,” Bjorndal told New
Scientist.

Likewise, the decline in Pacific sea otters started with native hunters about
2500 years ago. European fur traders accelerated the trend, and with the otters
nearly decimated, sea urchins began devouring kelp forests along the rocky
coast.

More modern fishing techniques began to cut a swathe through smaller and more
common animals over a century ago. For example, the dredging of oysters from
Chesapeake Bay started in the 1870s, depleting deep-water stocks within decades.
With few oysters left to filter the water, oxygen levels dropped, causing
problems by the 1930s.

Bjorndal says that there is still hope, however. “These ecosystems have not
been lost. With proper management we can restore them to health.” Because of the
vast size of the oceans, only a few species of large mammals have died out,
notably the Caribbean monk seal and the giant Steller’s sea cow. But she warns
that recovery may take a long time, with only small numbers of many
slow-breeding species like sea turtles left.

We also need to expand refuges where fishing is banned, says Peterson. With
protected areas, “we can achieve far higher harvests than if we harvested all
over.” But he warns that 10 per cent of all coastal areas must be protected to
reach that goal—a massive increase on today.