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The number of large fish, including tuna, marlin, swordfish,
sharks, cod and halibut, in the world’s oceans have dropped
by 90 percent in just 50 years, according to a study.
This means that only 10 percent of all large fish are left
in the ocean, and scientists are calling for an urgent restoration
attempt on a global scale.
Even more concerning is the finding that it takes industrial
fisheries only 10 to 15 years to diminish any new fish community
they encounter to one-tenth of its original size.
In the 10-year study, researchers assembled data sets representing
all major fisheries in the world and found that the impact
on ocean ecosystems has been vastly underestimated.
According to researchers, the depletion of these fish could
result in a complete re-organization of ocean ecosystems,
the global consequences of which are unknown.
Researchers constructed trajectories of biomass and composition
of large predatory fish communities from four continental
shelves and nine oceanic systems.
Additionally, to measure the decline of fish among open ocean
ecosystems, where it was thought there were still large reservoirs
of fish, researchers used Japanese long-lining data. Long-lines
are the most widespread fishing gear and are capable of catching
a wide variety of species over vast areas.
Surprisingly, the decline in fish spreads all the way to
the open ocean. According to researchers, in places where
long-lines used to catch 10 fish per 100 hooks, they are now
lucky to catch one.
While there was general acceptance of the data showing rapid
depletion of fish communities, some fishery managers found
the data "hard to accept," especially when in came
to individual species such as tuna.
Further, according to data, large predator fish are only
reaching sizes one-fifth to one-half what they used to be.
With the intense fishing pressure on the oceans today, many
fish do not even get the chance to reproduce, and many smaller
fish are caught and discarded before reaching maturity.
Researchers did see increases among some faster-growing fish
species. However, fisheries tend to focus on species that
are doing well, causing their increase in population to be
diminished before they get a chance to recover from past decreases.
Researchers say the solution to the problem is an overall
reduction in the percentage of fish killed each year. While
this may be difficult for fisheries initially, if fish populations
were restored, fisherman could get the same amount of fish
from the ocean with one-third to one-tenth of the effort required
now.
Creating marine reserves that are off-limits to fisherman
could also help. It would also likely increase the number
of fish in surrounding waters because once fish within the
reserves start to thrive they will inevitably spread beyond
the boundaries of the reserve.
However, measures to increase fish populations are urgent.
According to researchers, it’s important to understand
that some fish populations are very close to extinction and
could reach the "point of no return" if action isn’t
taken now.
Nature
May 15, 2003
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