41
Figures 6a and 6b. Downstream survival data collected for hatchery fish released at 5 locations in spring 2018. Two independent detection
sites 5 km apart produced similar survival estimates (6a, left) while the conceptual decline in abundance for a group of 1000 fish released in
the upper river is displayed on the right (6b). Figures provided by Kevin Pellett, DFO.
Figure 7. Great Blue Heron consumption estimates of juvenile
Chinook in comparison to river discharge (red dots) on hatchery
release date. Cowichan, 2017. No wild spawned juvenile Chinook
were tagged in 2017. Figure provided by Jeramy Damborg, BCCF.
83.6%
79.4%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
VIMY STOLTZ SKUTZ 70.2 ROAD POOL
ESTIMATED
SURVIVAL
2018 H- Allenby Detections
2018 H- North Arm Detections
69.2%
25.1%
15.8%
12.1%
7.3%
16.6%
30.9%
59.4%
Stoltz
Skutz
70.2 Trestle
Road Pool
Allenby
Vimy
y = -38.653x + 1000
y = -3.5325x + 275.94
0
200
400
600
800
1000
1200
0 5 10 15 20 25 30 35 40 45
ABUNDANCE
DISTANCE TRAVELLED (KM)
HATCHERY SURVIVAL 2018
Upper River
Lower River
1.7
1.7
5.4
0.8
0.9
0.8
1.9
16.2
8.8
4.6
28.1
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
2014 2015 2016 2017
COWICHAN
RIVER
FLOWS
(CMS)
RELATIVE
CHINOOK
CONSUMPTION
(%)
Hatchery Wild Discharge at Release 7 cms Base Flow
SIGNIFICANCE AND
RECOMMENDATIONS
The results of these studies have led to a change in
hatchery practices. DFO now releases Chinook smolts
at the hatchery or lower in the river, rather than at the
top of Cowichan River.
Other results will direct future lower river and estuary
rehabilitation projects targeting Chinook recovery.
These may include:
In-stream restoration of side channels with moderate
to high flows, and improving existing shoreline habitats
(e.g., riparian planting);
River flow manipulations and/or predator management
on Cowichan River;
PIT tag studies to assess in-river survival and predation
should be carried out in additional years and on other
river systems;
Evaluation of hatchery practices, release strategies
and locations. Lower survival of hatchery fish, which
are larger but less familiar with predators suggests that
changes in hatchery practices should be considered
and evaluated; and
Address minimum ecological flow needs for natural
production of Cowichan Chinook Salmon.
Photo
by
Ryan
Miller
