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Figure 1. A Rotary Screw Trap (RST) is used to carry out mark-recapture
studies of smolts and to estimate abundance of smolts.
THE IMPORTANCE OF FRESHWATER CONDITIONS
TO REARING PACIFIC SALMON
KEY QUESTIONS
A number of studies have been carried out on the
Cowichan River to further our understanding of Cowichan
Chinook early life history from the river to the inner
estuary. Studies examined habitat use by Chinook, relative
survival and interaction of hatchery and wild Chinook,
variation in survival and predation with river flow, and
ultimately the effect of freshwater rearing conditions on
early marine survival. These studies have been carried
out primarily by BC Conservation Foundation (BCCF),
DFO and UBC.
QUESTIONS ADDRESSED DATA CONCLUSIONS
What is habitat use and behaviour of
fry and fingerlings in Cowichan River?
Are there significant hatchery-wild
interactions in freshwater?
Are there significant freshwater
predators of Chinook and are losses
related to flow?
Sampling surveys in the Cowichan
River and Estuary.
Rotary Screw trap studies to assess
freshwater mortality 2014-2016.
PIT tag studies to assess freshwater
and early marine mortality 2015-2017.
Activated trail cameras, PIT tags
and antennas to examine potential
predators.
Adequate discharge, presence
of over-hanging vegetation and
instream riparian vegetation cover
were critically important for Chinook
fry rearing.
Freshwater survival was very low
in some years (as low as 20%) and
was related to river flows and in-river
predation.
There was a high level of freshwater
predation by herons on Cowichan
Chinook.
Overall survival rates of hatchery
fish were much lower than for wild
Chinook although they appear to be
similar for the first several months.
