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Wild salmon are tiny compared to the giant
ocean they call home, so it is not surpri-
sing that we know very little about where
they go and what they do when they get
there. But now, researchers working with
a project called Salmotrack are using the
latest available technology to learn as much
as they can about salmon movements in the
broad ocean.
"Pop-up satellite tagging"
One of the reasons we know so little about
wild salmon is due to their unusual life
cycle. Salmon spend their first few
years in a river, with each fish retur-
ning to spawn in the same river
where it grew up. But it has been
very difficult to follow them on their
ocean journeys once they leave their
home river for the sea.
"We know that in recent years,
salmon have had increased mor-
tality during the time they are at
sea, but much of the explanation
for this is due to conditions that we
do not understand. Until recently
it was simply impossible to follow
salmon during their wanderings in
the broad ocean. In contrast, it has
been much easier to follow an animal over
the water. But now we can finally uncover
the 'private' lives of salmon in the ocean
using satellite technology," says Professor
Audun Rikardsen, from the Department of
Arctic andMarine Biology at the University
of Tromsø. Rikardsen shows off a small
oblong "computer" that can be attached to a
salmon's back.
"This hangs on the fish and measures
depths and temperatures while they swim.
It also records sunrise and sunset. These are
the data we use to figure out where the sal-
mon has been and what it has been doing
in the ocean. The 'computer' is program-
med to release from the salmon at a specific
time. It then floats to the surface and sends
its data and position to a satellite, which
in turn sends the data to us. That's why it
is called 'pop-up satellite tagging'. It's like
Christmas Eve when we get into the data –
it's just incredibly exciting," he says.
Along the polar front
Based on the limited data they had, resear-
chers used to believe that when northern
Norwegian salmon headed out to sea,
they went to the region around the Faroe
Islands. But with the help of Salmotrack,
researchers now know that this is not usu-
ally the case.
Satellite tracking has shown that the salmon
spread out over a much larger area in
the Barents Sea, along the west coast of
Svalbard and in towards Greenland. Sal-
mon may travel as far as 80 degrees north,
which is the most northerly that salmon
have ever been recorded. Additionally, the
measurements show that salmon swim
much deeper than was previously thought.
"The equipment was first programmed to
make measurements to a depth of 550 met
res because we did not think that salmon
swam any deeper than that. But we see that
particularly during the winter, when there
is less food at the surface, salmon actually
swim far deeper than 550 metres. It is not
inconceivable that they dive significantly
deeper than that," Rikardsen says.
A preliminary analysis also shows that
salmon largely follow the productive zone
along the polar front, where the cold water
from the Arctic Ocean meets the warmwa-
ter from the northern extension of the Gulf
Stream. Salmon probably stay in this region
because it is where they find the most food.
Since 2008, more than 100 salmon have
been tagged, many of which are still swim-
ming around in the ocean right now. These
tagged fish have also been caught by sports
fishermen, and several local anglers have
aided the scientists in conducting their
research. Fish fromTrondheim Fjord,
Ireland and Greenland have also been tag-
ged, to learn where salmon from these areas
go when they are in the open ocean.
Uncovering the salmon's
private life
Unfortunately, the future for wild sal-
mon stocks looks rather bleak, and their
numbers are steadily declining in Norway.
Nevertheless, the situation for
salmon in Norway is better than in
the rest of Europe and on the eastern
side of North America.
"In the future, this new computer
technology will provide us with
important information about the
secrets of salmon and other marine
animals. It is very important for
future management to knowmore
about these issues, so that we can
make better forecasts and set bet-
ter quotas. There are six different
nations involved in this research,"
Rikardsen says.
Doesn't it bother the fish to swim around
with that thing on its back?
"It notices it, but it would be about the same
as if we were to wear a small, lightweight
backpack. Our data show that fish grow
normally and feel fine even when they are
fitted with the satellite tag. We are extrem-
ely careful in making certain that the tag
has minimal effect, because otherwise the
data are no good. For that reason, we only
tag the biggest fish we can, and have spent
a lot of time developing a good tagging
method," Rikardsen says.
Signals from the tagged salmon are picked up by a satellite andthen sent to
researchers' computers. Illustration: Audun Rikardsen/ Salmotrack
University of Tromsø –
Labyrint E/11
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Text:
Randi M. Solhaug
This little "computer" is attached to the salmon's back and
enablesscientists to track it by satellite. Photo: Salmotrack