NANFA-- Frog Decline Linked to Hatchery Fish

Jay DeLong (
Mon, 6 Aug 2001 21:17:24 -0700

Frog Decline Linked to Hatchery Fish - Kristian Foden-Vencil
August 1, 2001
Over the last 20 years, the population of wild frogs and toads has declined
dramatically in the Pacific Northwest and around the world. A team from
Oregon State University and Pennsylvania State University has been studying
the problem and now have several theories, including disease to habitat
degradation. The team unveiled a new theory today: that hatchery reared fish
are spreading a fungus called saprolegnia ferax which is fatal to toads and
frogs. Kristian Foden-Vencil has more.

In the study, scientists collected rainbow trout from the Wizard Falls Fish
Hatchery and freshly-laid eggs from western toads in Lost Lake, near the
Santiam Pass. They put the trout and eggs together in a laboratory and found
that the fish spread the fungus saprolegnia ferax to the toad embryos. In
fact, lead scientists Joseph Keisecker says death rates increased by about
15 percent.

Keisecker: It’s likely that the disease is on the fish themselves. On their
scales or in the mucus on their skin and when they’re introduced, it moves
off the fish either directly onto amphibians, or probably more likely onto
other substrates likes soil and comes in contact with amphibians at another
point in time.

The disease takes the form of a fungus living on the outer membrane of the
embryo. As the fungus grows it ruptures the membrane and smothers the embryo
eventually killing the toad. This study is the first solid evidence that
fish-stocks can spread amphibian diseases and as such, it has significant
implications. Hatchery-reared fish have been introduced to nearly half of
the 16,000 mountain lakes in the western United States. And fish are stocked
in a number of national parks and wilderness areas--like Lost Lake--so
anglers can enjoy their sport in areas where fish never used to live. But
Keisecker says the fact rainbow trout kill frogs and toads didn't really
surprise him.

Keisecker: When you introduce something like a trout, which is a predatory
fish, you know amphibians are a perfect prey item…. There’s a lot of studies
that have been done in Oregon, in California, in the western United States,
that have demonstrated that there’s pretty much a clear impact of
introducing fish on amphibians on native amphibians, especially in high
mountain lakes that haven’t had fish prior to these fish stocking regimes.

In these days of increased environmental sensitivity, the Oregon Department
of Fish and Wildlife has been cutting down on the number of lakes it stocks.
But agency fish biologist, Tom Murtagh, says high mountain fishing is such a
popular pasttime that it’s not a good idea to abandon the practice all

Murtagh: By putting trout into some of these high lakes it acts as a magnet,
so folks gravitate toward these high lakes. So the Forest Service has
pointed areas that are a little more fragile than others and might have
populations of amphibians of concern. And we’ve tried to identify those
lakes and either reduce the trout stock or cut it all together.

Concerns about the effect of hatchery trout on frogs and toads is not the
only concern surrounding high mountain lakes. The Fish and Wildlife Service
is starting to use native brown trout instead of other species because of
concerns that hatchery rainbow and brook trout will migrate downstream from
these lakes and compete with struggling salmon populations. Aubrey Russel of
the fish conservation group, Oregon Trout:

Russel: This is just another instance of where ODF&W has to come to grips
with the fact that introducing hatchery fish into rivers and lakes as
opposed to introducing wild and indigenous fish, contradicts with the agency
’s conservation mission.

Scientists say hatchery fish are only part of the problem of declining wild
frog and toad populations. Indeed, the Oregon and Pennsylvania State
Universities’ team have also found that climate change plays a large part:
less rain fall lowers the water levels of high desert lakes which in turn
means frog and toad embryos lie closer to the surface. Researchers believe
the closer to the surface the eggs are, the more they’re damaged by
ultraviolet light. But problems with diseased hatchery fish may have wider
implications than just frog and toad deaths. The Pew Oceans Commission
released a report this week, indicating that one in every three fish that
wind up as someone's dinner is now raised in some form of hatchery.

Jay DeLong
Olympia, WA, USA
"If the biota, in the course of aeons, has built something we like
but do not understand, then who but a fool would discard seemingly
useless parts? To keep every cog and wheel is the first precaution
of intelligent tinkering."
~ Aldo Leopold (1953)

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