[env-trinity] Sci.Amer.: Upstream Battle - What is Killing Off the Fraser River's Sockeye?

[Sari Sommarstrom]

<http://www.scientificamerican.com//>
Scientific American
<http://www.scientificamerican.com//>



Permanent Address: 
<http://www.scientificamerican.com/article.cfm?id=what-is-killing-off-fraser-river-sockeye-salmon>http://www.scientificamerican.com/article.cfm?id=what-is-killing-off-fraser-river-sockeye-salmon 



Upstream Battle: What Is Killing Off the Fraser 
River's Sockeye Salmon? [Slide Show]

A recent study suggests a mystery pathogen acting 
in concert with human-induced stressors may be the culprits

By 
<http://www.scientificamerican.com/author.cfm?id=1226>Anne 
Casselman  | Thursday, May 5, 2011 | 4

sockeye-salmon
  SPAWNING HOME: 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
Advertisement

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 
<http://www.scientificamerican.com/article.cfm?id=salmon-collapse-bad-news-for-bears>salmon 
run 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.

Now a study bolsters the hypothesis that a 
mysterious pathogen working in concert with other 
anthropogenic stressors may be the culprit.

Led by 
<http://www.dfo-mpo.gc.ca/index-eng.htm>Fisheries 
and Oceans Canada, 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.

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.

Months after the study came out mid-January in 
Science 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 Scientific American via e-mail.

"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.

<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

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.

"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."

Death by a thousand cuts
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.

"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.

He runs through a laundry list of factors that 
could amplify virus-driven disease mortality: 
<http://www.scientificamerican.com/article.cfm?id=warming-waters-exacerbate-dwindling-new-england-fisheries>fisheries 
shifting food chains, 
<http://www.scientificamerican.com/article.cfm?id=hunting-for-climate-change>global 
warming, marine pollutant–triggered toxic algae 
blooms, marine pollution in the form of chemical 
contaminants, and 
<http://www.scientificamerican.com/article.cfm?id=pesticides-may-block-male-hormones>endocrine 
disruptors altering the host–pathogen balance.

In Chinook salmon in Alaska's Yukon River, for 
example, the prevalence and mortality from the 
parasite Ichthyophonus 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.

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."

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.

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 
Science 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."

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.

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.

"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.

Dead fish swimming
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.

"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."

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.

The nearby 
<http://www.scientificamerican.com/article.cfm?id=earth-talks-salmon>Columbia 
River'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."

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, 
<http://www.pbs.org/wnet/nature/episodes/salmon-running-the-gauntlet/introduction/6546/>Salmon: 
Running the Gauntlet, 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.

"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.

Can science save the salmon?
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.

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.

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.

"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.

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.

"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."

--Francie Diep wrote and produced the slide show that accompanies this
story.

*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.

Scientific American is a trademark of Scientific 
American, Inc., used with permission

© 2011 Scientific American, a Division of Nature 
America, Inc. All Rights Reserved.


Email this Article

Upstream Battle: What Is Killing Off the Fraser 
River's Sockeye Salmon? [Slide Show]
Your Email Address Recipient's Email Address 
(separate multiple addresses with a comma) Comment (optional) X
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www2.dcn.org/pipermail/env-trinity/attachments/20110511/c417bb92/attachment.html>