[env-trinity] Over-fished species go into evolutionary overdrive: study

[Josh Allen]

Over-fished species go into evolutionary overdrive: study 


Wed Apr 16, 2:39 PM ET 

http://news.yahoo.com/s/afp/sciencegeneticsevolutionfishfoodbiodiversity


PARIS (AFP) - Relentless commercial fishing can trigger rapid
evolutionary changes when only smaller, younger fish are left behind, a
study released Wednesday shows. 

Moreover, those changes among fish populations -- a desperate bid to
adapt -- may be difficult or impossible to reverse.

Boom-and-bust cycles in over-fished species can wreak economic havoc on
fishing communities, and can trigger a downward spiral toward
extinction.

The study, experts say, could provide important clues on how to restore
fish populations that have, in many cases, been reduced by 90 percent
due to decades of industrial-scale fishing.

Scientists have long puzzled over the fact that populations of heavily
harvested fish, from sardines to tuna, fluctuate in size more
erratically than species that are not plucked from the sea for food.

To find out why, a team of researchers led by George Sugihara at the
University of California in San Diego poured over a rare set of data
tracking both fished and unfished species off the coast of California
over a period of five decades.

In considering three possible explanations, they found no evidence for
the first: that fluctuations in population simply mirrored the intensity
of commercial fishing.

They did find that the young fish left behind as too small to bring to
market were somewhat more vulnerable to the vagaries of the sea, whether
changing sea surface temperatures, currents or winds.

The critical factor, however, was not the impact of environmental
conditions on these age-imbalanced populations, but an intrinsic lack of
stability caused by such "juvenescence," as scientists call it.

The disappearance of older, bigger fish from the population induced
early maturation in the survivors in two ways, the study found.

In some cases the smaller fish actually adapted physically to new
conditions, changes that could be reversed.

But the researchers also found evidence for a genetic impact, adding
weight to a recent body of evidence suggesting that
environmentally-driven evolutionary changes can occur far more quickly
than once believed.

"The implication is that fisheries management need to give priority to
precautionary measures," said Nils Stenseth and Tristan Rouyer, both
from the University of Oslo, in a commentary, also published in Nature.

"When the ecological effects of fishing a particular population are
observed, the evolutionary consequences may have already set it, and may
be irreversible."

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