May 2019, ScientificAmerican.com 21ALEX MUSTARDGetty ImagesE C O L O G YCounting
Salmon
DNA in floating fish slime could
help monitor migrating salmonThe slime that sloughs off the skin of
Alaskan salmon might become the latest
tool for measuring their numbers and pro-
tecting populations—an effort that could
be vital to keeping the wild fish on dinner
plates for years to come. Researchers
recently counted the number of salmon
migrating through a narrowed waterway
for fish, or weir, in southeastern Alaska by
measuring DNA in the bodily waste they
shed into a stream as they headed to
spawning grounds.
Scientists have been developing this
approach, which relies on eDNA (or envi-
ronmental DNA), for years. They can
determine a fish species’ presence and get
a general idea of its abundance by measur-
ing the amount of its DNA in a sample of
water. But to maintain salmon populations
in a commercial fishery worth more than
$500 million a year, managers need a
more accurate way to count fish that
return from the ocean to spawn. Salmon
use thousands of streams throughout
Alaska; biologists can count them only at a
small subset because of the costs of travel-
ing to remote locations, building weirs that
funnel the fish for counting and paying
biologists who can accurately identify
salmon species.In the new study, Taal Levi, an assistant
professor of fisheries and wildlife at Ore-
gon State University, and his colleagues
collected daily eDNA samples at a count-
ing station at Auke Creek and compared
their results with human counts of sockeye
and coho salmon. They also recorded
streamflow, which affects how much
eDNA is present. After accounting for the
flow rate, Levi and his team accurately
matched eDNA concentrations with num-
bers of salmon counted. They reported
their findings online last December in
Molecular Ecology Resources.
The effort was a proof of concept, but
Levi hopes this approach can be applied to
other streams and automated to provide
more cost-effective monitoring. And
eDNA is already helping scientists track
the movement of salmon into the Canadi-
an Arctic, as the climate changes, by docu-
menting their presence in new locations.
Chris Habicht, a fisheries geneticist at
the Alaska Department of Fish and Game,
who was not involved in the work, is skep-
tical that this approach can be applied
broadly. He notes that biologists would
need to install streamflow sensors at each
site sampled—a costly endeavor in remote
parts of Alaska. Study co-author Scott
Vulstek, a fisheries biologist at the National
Marine Fisheries Service, admits there are
challenges. But not every unmonitored
stream is remote, he says, and eDNA
could supplement data collected at moni-
tored sites. Moreover, he adds, “this
technology is only going to get better
over time.” — Amy Mathews Amos© 2019 Scientific AmericanALEX MUSTARDGetty ImagesSCIENCE SOURCE
E C O L O G YCounting
Salmon
DNA in floating fish slime could
help monitor migrating salmonThe slime that sloughs off the skin of
Alaskan salmon might become the latest
tool for measuring their numbers and pro-
tecting populations—an effort that could
be vital to keeping the wild fish on dinner
plates for years to come. Researchers
recently counted the number of salmon
migrating through a narrowed waterway
for fish, or weir, in southeastern Alaska by
measuring DNA in the bodily waste they
shed into a stream as they headed to
spawning grounds.
Scientists have been developing this
approach, which relies on eDNA (or envi-
ronmental DNA), for years. They can
determine a fish species’ presence and get
a general idea of its abundance by measur-
ing the amount of its DNA in a sample of
water. But to maintain salmon populations
in a commercial fishery worth more than
$500 million a year, managers need a
more accurate way to count fish that
return from the ocean to spawn. Salmon
use thousands of streams throughout
Alaska; biologists can count them only at a
small subset because of the costs of travel-
ing to remote locations, building weirs that
funnel the fish for counting and paying
biologists who can accurately identify
salmon species.In the new study, Taal Levi, an assistant
professor of fisheries and wildlife at Ore-
gon State University, and his colleagues
collected daily eDNA samples at a count-
ing station at Auke Creek and compared
their results with human counts of sockeye
and coho salmon. They also recorded
streamflow, which affects how much
eDNA is present. After accounting for the
flow rate, Levi and his team accurately
matched eDNA concentrations with num-
bers of salmon counted. They reported
their findings online last December in
Molecular Ecology Resources.
The effort was a proof of concept, but
Levi hopes this approach can be applied to
other streams and automated to provide
more cost-effective monitoring. And
eDNA is already helping scientists track
the movement of salmon into the Canadi-
an Arctic, as the climate changes, by docu-
menting their presence in new locations.
Chris Habicht, a fisheries geneticist at
the Alaska Department of Fish and Game,
who was not involved in the work, is skep-
tical that this approach can be applied
broadly. He notes that biologists would
need to install streamflow sensors at each
site sampled—a costly endeavor in remote
parts of Alaska. Study co-author Scott
Vulstek, a fisheries biologist at the National
Marine Fisheries Service, admits there are
challenges. But not every unmonitored
stream is remote, he says, and eDNA
could supplement data collected at moni-
tored sites. Moreover, he adds, “this
technology is only going to get better
over time.” — Amy Mathews Amossad0519Adva3p.indd 21 3/21/19 3:21 PMThe #1 In Value—Guided Tours Since 1952Grand Canyon; Monument Valley;
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