for release until Thursday, 9 January 2003 at 14:00 U.S. Eastern Time
to anchovies and back in 50 years—
Local fisheries part of
bigger cycle affecting
entire Pacific Ocean
MOSS LANDING, California—In
the late 1930s, California's sardines supported the biggest fishery in
the western hemisphere, with more than half a million tons of fish caught
each year. By the mid-1950s, the sardines had virtually disappeared.
Although fishing pressure may have played a part in this process, new
research published in the current issue of Science indicates that the
sardines' demise was part of a 50-year cycle that affects not just
California, but the entire Pacific Ocean.
Francisco Chavez, a biological
oceanographer at the Monterey Bay Aquarium Research Institute (MBARI) and
lead author of the study, combined a hundred years of data on physical
oceanography, marine biology, and meteorology to examine long-term cycles
in different parts of the Pacific Ocean. He points out that sardine
catches in California, Japan and Peru followed parallel trends, despite
being on opposite sides of the ocean and facing different amounts of
fishing pressure. More importantly, when sardine catches in both areas
went bust, anchovy catches boomed. Chavez's research indicates that this
alternation between a "sardine regime" and an "anchovy
regime" involves much more than just fisheries. As he puts it,
"Fish in many parts of the Pacific are marching to the same drummer.
This same drummer is causing changes in ocean circulation and in the
global carbon cycle. What we've been trying to find out is, what is the
drummer, and is the beat going to change?"
the last hundred years, some decades have seen huge schools of sardines
flourish off the Central California coast; during other decades, the small
fish have been virtually nonexistent. These changes may be symptomatic of
long-term (50-year) cycles that affect the entire Pacific Ocean.
(Photo copyright © 1994 Monterey Bay
To this end, Chavez gathered
data from fellow scientists, not just on fisheries biology, but on
sea-surface temperature, elevation, and currents, atmospheric carbon
dioxide concentrations and circulation, global air temperature, and more.
Despite considerable year-to-year variability, Chavez found parallel
trends across the entire Pacific when he looked at three-year averages and
subtracted out gradual long-term increases (such as that of carbon
dioxide). These trends show that sardine and anchovy regimes alternate
about every twenty five years, and that the most recent shift (from
sardines to anchovies) occurred in the late 1990's.
These cycles are similar to the
familiar El Niño and La Niña events, but take place over longer time
periods and have greater effects at mid- and high latitudes. For example,
average conditions during a sardine regime are analogous to those during
an El Niño event, when coastal waters off of Peru and California become
warmer than usual. Less nutrient-rich deep water is brought the surface,
so phytoplankton populations remain relatively low. This affects the
entire marine food web, resulting in fewer zooplankton, anchovies,
seabirds, and even salmon and rockfish. In contrast, the waters off Japan
and the north-central Pacific respond oppositely, with increased
productivity. Surprisingly, sardines tend to be more common on both sides
of the north Pacific during these periods. During an anchovy regime, all
of these trends are reversed.
highly simplified graph shows how the Pacific Ocean has alternated between
“sardine regime” and “anchovy regime” over the past 70 years.
These two regimes involve not just fish, but changes to ocean
and the atmosphere across the entire Pacific Ocean.
Chavez hopes that by studying
these long-term cycles, scientists will be able to better understand the
effects of human activities. A prime example is the demise of the
sardines. Chavez comments, "At least for these fast-growing fish,
commercial fisheries are not always the sole cause of the collapse."
Similarly, he points out that studies of global warming based on data
collected over several decades could be strongly influenced by these
natural, multi-decadal oscillations.
Chavez admits that his article
may be controversial and hopes that it will stimulate scientific
discussion about these long-term cycles, and especially about their
possible causes. He remarks, "During the peer-review process for this
paper, one reviewer called it imaginative. And it is. If we had the ocean
wired with a network of instruments and ocean observatories, then we would
need less imagination and could understand this a lot better."
Media contact: Debbie Meyer, email@example.com,