20 February, 2005
BBC News science reporter, in Washington DC
The shrinking size
of fish due to their overexploitation has dire consequences for
the recovery of depleted stocks, scientists have claimed.
Fishing drives natural
selection for smaller fish that grow more slowly and have reduced
These changes are
genetic and therefore hard to reverse, scuttling the renewal of
dwindling fish populations.
Details of the
research were discussed on Saturday at a major science conference
in Washington DC.
are collapsing and many are on the brink of potentially
irreversible loss," said Jeremy Jackson, of the Scripps
Institution of Oceanography in California.
massive evolutionary shifts going on in the remnant populations of
fish. Large fish with huge reproductive potential are being
replaced by smaller fish with diminished reproductive
potential," he told the annual meeting of the American
Association for the Advancement of Science (AAAS).
David Conover, of
Stony Brook University in New York found a two-fold change in
productivity in Atlantic silversides within just four generations
harvesting the largest fish, we end up changing the whole biology
- not only growth rates, but egg size, fecundity, feeding
behaviour," he said.
"The scary part
is that when we stopped size-selective harvest, the biology didn't
change back, it was permanent."
Research by Dr Conover
and other groups in Norway, Canada and Austria also found declines
in the reproductive potential of fish populations.
Work by Steven
Berkeley, of the University of California-Santa Cruz, shows that
older and therefore bigger female Pacific rockfish produce
exponentially more eggs than younger, smaller females and their
larvae have a greatly increased chance of survival.
"What we need to
provide is some refuge from fishing so that the genes for larger,
faster-growing fish have some sanctuary from fishing," said
Andy Rosenberg, of the
University of New Hampshire, said that the way fish resources were
currently being managed was prolonging the period of recovery for
"The longer we
ignore these fine-scale processes, the longer it will take for
that recovery. And it's not a simple linear relationship - you can
cause massive damage in a very short period of time and it can
take them much longer to recover," he said.
Cod off the coast of
Newfoundland - once one of the largest fish populations in the
world - have suffered a 99% decline since the 1960s.
Research shows that
changes in size and age at maturity caused by just 30-50 years of
fishing have reduced the chance of cod's recovery by 25-30%.