6 fall/winter 2016 psf.ca
THE PROJECT: Since 2010, a team of
researchers from UBC led by Dr. Scott
Hinch has been tracking Sockeye smolts
from the Chilko River – one of the
largest Sockeye populations in British
Columbia – through the Fraser to
the Strait of Georgia. The purpose
is to figure out where salmon are
dying en route to the ocean, and
what is causing that mortality.
LESSONS LEARNED: Sockeye
smolts experienced poor survival
in the Chilko River, but nearly 100
per cent survived the journey down
the Fraser. One big reason: bull trout.
The clear, slow-moving waters of the
Chilko made it easy for bull trout to prey
on salmon and literally gorge themselves.
Lab tests revealed that small bull trout
were eating 5 to 12 percent of their body
weight in one day (the equivalent of a
180-pound person eating 10 to 20 pounds).
But in the Fraser River, fast flows and
murky waters allowed salmon to evade
predators.
"Another key discovery was that these
little fish could find safety in numbers,
also called 'predator swamping'," explains
Nathan Furey, one of the lead researchers.
"We found that smolts migrating in large
numbers had survival rates exceeding
90 per cent, in comparison to less than
50 per cent for smolts travelling in small
numbers. This information will be key
for future management. We will be able
to provide much more refined estimates
for juvenile salmon survival based on the
volume of fish that migrated out at one
time. These numbers for smolts expected
to survive are important because they are
used to estimate adult returns."
n
SALISH SEA BREAKTHROUGHS
Binge-feeding Bull Trout
and Safety in Numbers
Researchers found bull trout stomachs were
often packed with 20 or more salmon smolts,
with some containing more than 60. Right: A
Steelhead smolt recovers after being implanted
with a tiny tracking tag.
