|
Environmental variability is a key feature of
exploited or pristine ecosystems and has very
significant implications for production,
development and management of fisheries. The
frequency of observed changes and the amplitude of
these changes vary widely.
The El Niño phenomenon of 1997-98,
and the associated massive media coverage, provided
a primer on oceanography to millions of people
around the world. More than 60 countries suffered
heavy floods or severe drought as a result of
weather anomalies caused, at least in part, by the
phenomenon's cyclical warming of surface waters off
the coast of Peru. Between April 1997 and April
1998, floods were reported in over 40 countries,
droughts or dry spells in 22 countries and two
countries suffered widespread forest fires.
Furthermore, countries can be subjected to a double
whammy when an El Niño event is immediately
followed by a La Niña event. La Niña
is characterized by an upwelling of cold water in
the areas of the Pacific that may bring drought to
areas hit by floods during El Niño, and
flooding to those hit by drought.
The combination of El Niño and La
Niña events provide extreme examples of
environmental variability that made international
news almost every day during 1997-98. Reports dealt
with the devastating effects of the floods,
droughts and forest fires. Fishery resources,
although not the object of such media attention,
were any less affected.
In fact, as information on variability in fish
populations accumulates over long periods, it seems
that many of the world's largest fish stocks are
growing and declining in relative synchrony. The
simultaneous rise and fall of sardine (pilchard)
populations in widely separate areas of the Pacific
Ocean was first pointed out at the major FAO Expert
Consultation in 1983. Since then, the pattern
reported has continued to hold, including an
additional episode of a simultaneous pattern change
from population growth to abrupt decline.
Other examples include the Peruvian anchoveta
(which grew to support the largest fishery that has
ever existed), the Southern African pilchard
fisheries and the Japanese flying squid, which all
rose and peaked between the late 1950s and early
1970s during which time the large Pacific pilchard
stocks essentially vanished.
The early period from the 1970s to the
mid-1980s, which saw the massive rises of sardine
stocks in the Pacific and the collapse of the
Peruvian anchoveta in the Pacific and the Southern
African pilchard in the Atlantic, was also a
remarkable period of global average temperature
rise, suggesting the likelihood that climatic
variability may be the driving force linking these
variations. However, it seems unlikely that
temperature alone could be the major causal agent,
since the sea temperatures on the eastern and
western sides of the Pacific Ocean tend to vary out
of phase rather than in phase. This was also a time
of enhanced El Niño conditions, marked by a
long-period progressive collapse of the Southern
Oscillation Index, commencing with the 1972 El
Niño and culminating in the major 1982-83 El
Niño episode.
Clearly, no one is yet sure that these
ostensible patterns are anything more than
fortuitous happenstance, nor has a comprehensive
objective analysis been produced. However, there is
no doubt that if there does exist a truly effective
climatic linkage mechanism which acts to
synchronize variability in many of the largest and
most important fish populations of the world, it
has very interesting and important implications for
management of the global fish supply, food
security, and for understanding - even predicting -
fishery resource variability.
Whatever its sources might be, natural
variability adds to the uncertainty about the
working of exploited ecosystems, their resilience
to human impacts and their capacity to recover from
serious disturbances. It therefore contributes to
the need for wide implementation of the
precautionary approach to fisheries.
|
