http://story.news.yahoo.com/news?tmpl=story&u=/afp/20030604/sc_afp/science_biodiversity_030604184038
Farmed
salmon pose greater risk to wild species than thought
Wed Jun 4, 2:40 PM ET
PARIS (AFP) - Farmed
salmon are a bigger risk to wild species
than previously thought, according to a study which says young
captive fish that escape their pens beat their native counterparts
at the mating game.
Salmon farms are a
thriving industry in Canada, Chile, Ireland,
Norway and Scotland but biologists have long feared that the native
gene pool could be destroyed if too many penned fish escape their
confinement and inter-breed with wild fish.
Until now, those fears
have been dampened by findings that
escapees are less successful at reproducing than native fish.
But a new study says
the picture is more complex, the British
weekly New Scientist reports in its forthcoming June 7 issue.
Farmed salmon may be
less fertile than wild fish but young males
among them more than make up for it. Their early sexual maturity
and aggressiveness enables them to sneak in front of larger
wild fish to fertilise the female's eggs.
Experiments conducted
on farmed, wild and hybrid species of
Norwegian salmon by Oxford University scientist Dany Garant
and colleagues found that farmed yearlings were four times
as successful as wild ones at fertilising eggs.
Even the hybrids were
twice as good at it as their wild rivals.
Given the faster life
cycles of farmed salmon, these young fish
could very quickly spread their genes through wild populations,
says Garant's study, published in a specialist journal, Ecology
Letters.
William Muir, an expert
on farmed and transgenic fish at Purdue
University in the US state of Indiana, told New Scientist that
the study shed "incredibly important" light on the dilemma
of
farmed fish.
"(Escapees) could
swamp the gene pools with maladapted genes
and quickly cause extinction of wild fish," he warned.
Seven countries that
have big salmon farming industries signed
an agreement in 1994 aimed at minimising the impact of fish
farming in the North Atlantic.
But the measures set
out in the accord are only voluntary
guidelines and do not hold countries accountable for damage
wrought by escaped fish.
Escapees are a major
problem, said Garant. "In Norway,
some rivers are completely invaded by farmed fish."
