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<h2><b><a href="??">Upstream Battle: What Is Killing Off the Fraser
River's Sockeye Salmon? [Slide Show]</a> </b></h2>A recent study suggests
a mystery pathogen acting in concert with human-induced stressors may be
the culprits<br><br>
By <a href="http://www.scientificamerican.com/author.cfm?id=1226">Anne
Casselman</a> | Thursday, May 5, 2011 | <a href="#comments">4</a>
<br><br>
<img src="http://www.scientificamerican.com/media/inline/what-is-killing-off-fraser-river-sockeye-salmon_1.jpg" width=277 height=277 alt="sockeye-salmon">
<b>SPAWNING HOME:</b> Adult sockeye return to their birthplace,
Scotch Creek, to spawn before dying. Scotch Creek is located in South
Central British Columbia and feeds into the Fraser River, home to one of
the world's largest wild sockeye salmon runs. Image: © Matt Casselman
<br>
Advertisement <br><br>
Gridlocked bridges over the Fraser River are just a part of life for
commuting Vancouverites. But the industrialized motif of North America's
longest dam-free river belies a rare natural treasure: a sockeye
<a href="http://www.scientificamerican.com/article.cfm?id=salmon-collapse-bad-news-for-bears">
salmon run</a> with a historical average of eight million fish worth over
$1 billion. Since the early 1990s the numbers of Fraser sockeye have
steadily dwindled, reaching a particularly troublesome nadir in 2009 when
more than 11 million sockeye were forecast to return and only 1.4 million
showed up. Since the mid-1990s, something began killing large numbers of
returning sockeye on the Fraseranywhere from 40 to 95 percent of fish in
some yearsbefore they could spawn.<br><br>
Now a study bolsters the hypothesis that a mysterious pathogen working in
concert with other anthropogenic stressors may be the culprit.<br><br>
Led by <a href="http://www.dfo-mpo.gc.ca/index-eng.htm">Fisheries and
Oceans Canada</a>, a team of scientists tracked returning Fraser River
sockeye to see whether the genetic activity of those that successfully
spawned differed from the activity of those that perished prematurely en
route.<br><br>
Sure enough, salmon with a certain pattern of gene expression in their
gill tissue were 13.5 times more likely to die than those that didn't
carry the "you've not got long to live" signature, as co-author
and University of British Columbia (U.B.C.) fish physiologist Tony
Farrell puts it. Most intriguingly the mortality-related genomic
signature in the fish resembled that triggered by a viral infection.
"This was a needle-in-haystack investigation, so we were more than
pleased that we identified a signature, and then to narrow it down to
what might be a viral signature was surprising," says
Farrell.<br><br>
Months after the study came out mid-January in <i>Science</i> the
research continues to make waves on Canada's west coast as journalists
and environmentalists speculate as to whether the genomic signature
identified in the study might be evidence of an epidemic of salmon
leukemia, known to have plagued salmon fish farms along British
Columbia's coast.* Lead study author Kristi Miller-Saunders, a molecular
geneticist at Fisheries and Oceans Canada in Nanaimo, has not been given
the green light to speak freely with the press, however she did respond
to questions from <i>Scientific American</i> via e-mail.<br><br>
"One of the most important findings of this study was the fact that
salmon were already compromised before entering the river" on their
journey home to spawn, she wrote. The scientists are currently studying
juvenile salmon to see if the genomic signature is already present before
they go out to the open ocean. Miller-Saunders also reports "there
is some indication that the signature may be in Chinook and coho"
salmon, too.<br><br>
<b><i>
<a href="http://www.sciam.com/slideshow.cfm?id=what-is-killing-off-fraser-river-sockeye-salmon">
View a slideshow of salmon species potentially affected by the
virus<br><br>
</a></i></b>Unpublished studies have found the signature in other cohorts
of Fraser sockeye, suggesting that the phenomenon spans different years.
But the mystery virus remains unidentified. Attempts by Miller-Saunders's
lab to culture the virus from affected tissue and do molecular screenings
of known pathogens have come up empty. Currently she is attempting to
sequence the pathogen from the tissues of affected fish.<br><br>
"The possibility of a disease affecting these fish has been on the
table long before this paper came out and the usual suspect has been fish
farms," says John Reynolds, a salmon conservation scientist at Simon
Fraser University in Burnaby, British Columbia. "My impression is
that the hard evidence isn't there yet to either implicate fish farms or
to let them off the hook."<br><br>
<b>Death by a thousand cuts<br>
</b>The study only correlates a genomic signature with mortality, rather
than proving any causal relation, but it also hints at how genomic
markers can inform better management of the dwindling sockeye
stocks.<br><br>
"The question is: Is disease getting worse by combinations with
other either natural or anthropogenic stressors?" says Jim Winton, a
microbiologist at the U.S. Geological Survey's (USGS) Western Fisheries
Research Center in Seattle.<br><br>
He runs through a laundry list of factors that could amplify virus-driven
disease mortality:
<a href="http://www.scientificamerican.com/article.cfm?id=warming-waters-exacerbate-dwindling-new-england-fisheries">
fisheries</a> shifting food chains,
<a href="http://www.scientificamerican.com/article.cfm?id=hunting-for-climate-change">
global warming</a>, marine pollutant–triggered toxic algae blooms, marine
pollution in the form of chemical contaminants, and
<a href="http://www.scientificamerican.com/article.cfm?id=pesticides-may-block-male-hormones">
endocrine disruptors</a> altering the host–pathogen balance.<br><br>
In Chinook salmon in Alaska's Yukon River, for example, the prevalence
and mortality from the parasite <i>Ichthyophonus</i> has recently risen
in concert with climate change, which has increased river temperatures by
an alarming 5 degrees Celsius. "At these higher temperatures, this
disease goes much faster," Winton explains.<br><br>
The rise in mortality of Pacific herring in Puget Sound tells a similar
story. There, Winton's lab has identified "three candidate diseases
that we believe are now much worse than they used to be…. So there are
cases in wild populations where we believe changes, and many of them
man-induced, are altering the impact of natural mortality from
disease."<br><br>
The Fraser River itself has undergone considerable warming. Seven of the
past 10 summers have broken records as the warmest. River temperatures
are nearly two degrees C warmer than 50 years ago, a problem for these
cold-blooded fish.<br><br>
In the twilight of their brief lives adult Pacific salmon migrate back to
their river of birth to spawn, perpetuating a four-year life cycle that
boomerangs thousands of kilometers into the ocean. "These are very
old fish, imagine these are like your grandmothers and
grandfathers," says Scott Hinch, a salmon ecologist at the U.B.C.
who co-authored the <i>Science</i> paper. By the time Pacific salmon
close in on their spawning grounds, they are senescent and naturally
immunosuppressed. "So any small disease, parasite, illness that is
naturally occurring that is there they will pick up, and then it's often
a race against time."<br><br>
The salmon naturally expire after the Herculean effort of swimming
upstream and spawning, but too many fish perishing prematurely before
they've had a chance to lay eggs and fertilize them spells
trouble.<br><br>
Aquatic pollution may further exacerbate things. "We believe that
some of the classes of contaminants that are now in the environment, such
as these endocrine disruptors coming out of sewage treatment plants, are
having an impact on the immune function in fish and altering disease
resistance," Winton says. Likewise, the Fraser River sockeye
are met with sewage outflows from Vancouver at the river's mouth in the
Strait of Georgia.<br><br>
"Personally, I think changing the environmental quality in the
Strait of Georgia is a major part of this explanation for the Fraser
sockeye as well," says Brian Riddell, CEO of the Pacific Salmon
Foundation in Vancouver.<br><br>
<b>Dead fish swimming<br>
</b>To further muddy the already murky waters are the "early
migrating late runs". If it sounds paradoxical, that's because
everything about these fish runs counter to reason. These are sockeye
that historically migrated late in the spawning season but recently have
begun to jump earlier by several weeks. All one really needs to know
about this cohort is the term Hinch has coined for them: "dead fish
swimming". That and the fact that the majority of fish sampled in
Miller-Saunders's study, the ones carrying the mortality-related genetic
signature, were part of these early migrating late runs.<br><br>
"Generally the earlier migrating fish are the ones that are
dying," Hinch says. "The grand picture is that these fish are
screwed basically when they come back."<br><br>
Since 1996 a larger and larger percentage of the late runs have begun to
come back two to three weeks (at most, a month) early. These days,
anywhere between 40 and 95 percent of the late runs are migrating earlier
when river temperatures are much higher than what they would historically
encounter. Research by Hinch and his colleagues found that the early
migrating late-run fish differ physiologically from their normal-timed
counterparts. They are more reproductively mature, stressed, and their
physiology is precociously oriented toward the freshwater environment.
"So not only are they forced to deal with [river] temperatures that
are potentially lethal, they're also what appears to be compromised in
some fashion," Hinch says.<br><br>
The nearby
<a href="http://www.scientificamerican.com/article.cfm?id=earth-talks-salmon">
Columbia River</a>'s sockeye, along with steelhead (also known as rainbow
trout), which face temperatures 2.5 degrees warmer than the historical
average, have shifted their migration times to avoid peak summer
temperatures. Not so with the Fraser's early migrating late runs, which
migrate right when the river is warmest. "Clearly this is not an
adaptive strategy to climate change," Hinch says. "The fact
that it's not getting selected against suggests that there's something
annually causing this to happen and a disease makes a sense."<br>
<br>
Even though the Columbia River's fish seem to be better at adapting their
migration patterns than the fish on the Fraser, that's not to say that
it's the model to follow. "The Columbia [River] is a great
cautionary tale as they consider what to do about the salmon situation up
there," says the director of a new PBS documentary,
<a href="http://www.pbs.org/wnet/nature/episodes/salmon-running-the-gauntlet/introduction/6546/">
<i>Salmon: Running the Gauntlet</a></i>, Jim Norton. The film
investigates collapsing Pacific salmon populations all down the Pacific
Northwest and examines how biologists and engineers are trying to better
manage the region's threatened salmon runs.<br><br>
"The Columbia's message to the Fraser is: In the consideration about
how to respond to changes you don't yet understand, be very clear that
once you break the system, no amount of money, creativity or engineering
will ever get the pieces back together again," Norton says.<br><br>
<b>Can science save the salmon?<br>
</b>The large number of missing Fraser River sockeye in 2009 prompted a
Canadian federal judicial inquiry into the matter, the Cohen Commission.
And just to underscore how little scientists understood of the fish, the
sockeye run in 2010 was a once-in-a-century bonanza, with 34 million fish
flooding the river. "From a historic low to a historic high
almostthat creates a lot of uncertainty for management but it also
raises questions on why it's swinging so much," says U.B.C.'s
Farrell. The USGS's Winton points out that the sockeye run of 2010 was an
anomaly, in the face of a steady and worrisome decline in Fraser sockeye
over the years.<br><br>
The Cohen Commission is currently underway and study co-author Hinch was
called to the stand as a witness in mid-March. "Moving forward the
real issue is whatever this is, what do we do now and how do you manage
in the face of it," he says.<br><br>
Miller-Saunders, for her part, will go on the stand later this summer to
speak about her research, which has already been referenced in the
enquiry's proceedings. Up until then, it is unlikely that she will be
allowed to speak freely to the media about her research. British Columbia
Supreme Court Justice Bruce Cohen, the commissioner who is overseeing the
investigation, is in the unenviable position of hearing everyone out and
making recommendations to ensure the future sustainability of the fishery
by June 2012.<br><br>
"We will have a full hearing session on diseases and the impact, if
any, of aquaculture. The interplay between climate change warming and
pathogens, if any, will be part of that subject," says Brian
Wallace, senior commission counsel.<br><br>
The Canadian Department of Fisheries and Oceans also has to juggle an
immense number of stakeholders and their needs when managing the Fraser
sockeye: coastal fisheries with different gear types, the in-river First
Nations harvest, and one of the largest recreational fisheries in
Canada.<br><br>
"They were hoping that our research would tell them what do you do
and our research is telling them this is tough," Hinch says.
"So we're probably never going to come up with the exact cause but
we may be well able to piece together a series of potential
causes."<br><br>
<i>--Francie Diep wrote and produced the slide show that accompanies
this<br>
story.<br><br>
*Clarification (5/5/11): This sentence was modified after publication to
change the tense of the verb describing when leukemia has plagued salmon
fish farms along British Columbia's coast. <br><br>
</i>Scientific American is a trademark of Scientific American, Inc., used
with permission <br><br>
© 2011 Scientific American, a Division of Nature America, Inc. All Rights
Reserved. <br><br>
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