February 21, 2005
New findings lead researchers to question
basic assumptions of fisheries management
By Tim Stephens
Biologists speaking at a symposium in Washington, D.C., last
week warned that fundamental assumptions underlying current
fisheries management practices may be wrong, resulting in management
decisions that threaten the future supply of fish and the long-term
survival of some fish populations.
Research by UCSC's Steven Berkeley on black rockfish, shown
in the Monterey Bay National Marine Sanctuary, showed that
larvae produced by large, old females are more likely to
survive than the offspring of younger fish.
Photo: Kip Evans |
The symposium, organized by Steven Berkeley of UCSC and Larry
Crowder of Duke University Marine Laboratory, was part of the
2005 Annual Meeting of the American Association for the Advancement
of Science (AAAS).
"Much of what we now know about fish populations is not
being accounted for in current fisheries management," said
Berkeley, a research biologist at UCSC's Long Marine Laboratory.
Berkeley's research on West Coast rockfish, for example, shows
that large, old females are far more important than younger
fish in maintaining productive fisheries. The larvae produced
by these "big, old, fat females" grow faster, resist
starvation better, and are much more likely to survive than
the offspring of younger fish.
Unfortunately, older fish tend to disappear under current fisheries
management practices--the old fish get caught and the younger
fish never have a chance to grow old.
"Our research shows that you need to maintain older fish
in the population because those are the most successful at reproducing.
But normal fishing at what we now think of as safe levels will
not maintain old fish in the population," Berkeley said.
The effects of fishing on the age structure of a population
is particularly striking in the various species of rockfish,
which are very long-lived fish. Many rockfish can live for 50
years or more, and some species can live well over 100 years.
Current fisheries management actually aims to reduce the number
of old, slow-growing fish in the population, leaving more room
and resources for younger, faster-growing fish. Most marine
fish produce huge numbers of eggs and larvae, so the assumption
has been that the spawners that remain after harvesting will
produce plenty of larvae to replenish the population. According
to Berkeley, however, elimination of older generations drastically
reduces the ability of the population to replenish itself.
Failure to account for the role of older fish in maintaining
healthy populations may help explain the recent collapse of
some major West Coast fisheries. The Pacific Fishery Management
Council has declared several stocks of groundfish--a group that
includes numerous species of rockfish and other bottom-dwelling
fish--to be overfished. Tight restrictions were imposed to allow
the overfished populations to recover, causing economic hardship
for many in the West Coast fishing industry. Recovery of some
stocks is expected to take decades.
One way to prevent such problems may be to establish marine
reserves--areas where fishing is not allowed and fish populations
are able to age naturally.
"Marine reserves are the only good way of protecting the
full age structure of a population of fish, so that at least
some of the population ages naturally," Berkeley said.
"There may be other approaches, but no matter how you manage
the fishery, you can't have a full complement of age classes
unless some part of the population is off limits."
Other research presented at the symposium includes new findings
about genetically distinct populations within the geographic
ranges of some marine fish species, as well as evidence that
successful breeders may be few and far between in some populations.
These and other findings further undermine fundamental assumptions
of current fisheries management, Berkeley said. "These
are all things that should make us stop and think about how
we manage fisheries," he said.
In addition to Berkeley, UCSC graduate student Martha Burford
also presented results from her research at the symposium.
Berkeley and his collaborators have published recent papers
on their research and its implications for fisheries management.
Findings on the influence of maternal age on larval growth and
survival appeared in the May 2004 issue of Ecology. Management
implications of these and other findings were discussed in a
paper in the August 2004 issue of Fisheries.
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