Monday, September 26, 2011

'Illusion of Plenty' Masking Collapse of Two Key Southern California Fisheries

Scripps-led study finds overfishing of spawning areas, environmental
conditions behind collapse of two bass species

Scripps Institution of Oceanography/University of California, San Diego

The two most important recreational fisheries off Southern California have
collapsed, according to a new study led by a researcher from Scripps
Institution of Oceanography at UC San Diego.

Scripps postdoctoral researcher Brad Erisman and his colleagues examined the
health of regional populations of barred sand bass and kelp bass-staple
catches of Southern California's recreational fishing fleet-by combining
information from fishing records and other data on regional fish
populations. Stocks of both species have collapsed due to a combination of
overfishing of their breeding areas and changes in oceanographic conditions,
the researchers found.

As they describe in the most recent edition of the Canadian Journal of
Fisheries and Aquatic Sciences, the researchers say the total amount, or
biomass, of each bass species decreased 90 percent since 1980. Yet fisheries
catch rates have remained stable for a number of years, even as overall
population sizes dropped drastically. This is due, the authors say, to a
phenomenon known as "hyperstability" in which fishing targets spawning areas
at which large numbers of fish congregate, leading to a misleading high
catch rate and masking a decline in the overall population.

"The problem is when fish are aggregating in these huge masses, fishermen
can still catch a lot each trip, so everything looks fine-but in reality the
true population is declining," said Erisman, a member of the Scripps Center
for Marine Biodiversity and Conservation. "So as the true abundance is
declining, the fisheries data used to assess the health of the fisheries are
not showing that and give no indication of a collapse-this is referred to as
'the illusion of plenty.'"

Erisman says the cod fishery that collapsed in the North Atlantic Ocean is
the world's most famous example of fisheries data masking an impending
collapse, but other fish stocks in regions where fish congregate to spawn
are declining as well.

In order to grasp a clear picture of the true health of the barred sand bass
and kelp bass in Southern California, Erisman and his colleagues looked
outside fisheries data. They tapped into fish population numbers tracked by
power plant generating stations, which are required to log fish entrapments
as part of their water cooling systems, and underwater visual censuses
conducted by Occidental College since 1974.

The authors acknowledge that both bass species began declining in the early
1980s, a drop other studies have directly linked with a climatic shift in
regional water temperatures. But they say fishing impacts exacerbated the
declines.

"The combined evidence from this study indicates that persistent overfishing
of seasonal spawning aggregations by recreational fisheries brought about
the collapse of barred sand bass and kelp bass stocks in Southern
California," the authors write in their paper.

"The relationship between catch rate and stock abundance suggests there is
an urgent need to incorporate fisheries-independent monitoring to create
something sustainable and monitor the fisheries effectively," said Erisman.
"While fisheries monitoring remains a key part of management, it is clear
that such data alone do not provide an accurate assessment of stock
condition."

Larry Allen of California State University Northridge; Jeremy Claisse and
Daniel Pondella II of Occidental College; Eric Miller of MBC Applied
Environmental Sciences; and Jason Murray of the University of South Carolina
coauthored the study.

The research was supported by Scripps' Center for Marine Biodiversity and
Conservation, the Walton Family Foundation and the David and Lucile Packard
Foundation. The Vantuna Research Group (Claisse and Pondella) of Occidental
College has been supported by Chevron.

About Scripps Institution of Oceanography Scripps Institution of
Oceanography at University of California, San Diego, is one of the oldest,
largest and most important centers for global science research and education
in the world. Now in its second century of discovery, the scientific scope
of the institution has grown to include biological, physical, chemical,
geological, geophysical and atmospheric studies of the earth as a system.
Hundreds of research programs covering a wide range of scientific areas are
under way today in 65 countries. The institution has a staff of about 1,400,
and annual expenditures of approximately $170 million from federal, state
and private sources. Scripps operates robotic networks, and one of the
largest U.S. academic fleets with four oceanographic research ships and one
research platform for worldwide exploration. Learn more at scripps.ucsd.edu.

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