Bottleneck Program Study Areas

Figure 1. The map of the Bottlenecks Program's study area (Northern Salish Sea / Strait of Georgia) showing rivers which have PIT tagging and PIT infrastructure

Figure 1. The map of the Bottlenecks Program’s study area (Northern Salish Sea / Strait of Georgia) showing rivers which have PIT tagging and PIT infrastructure

Cowichan River Study Area

Cowichan Bay is a sheltered bay located on the southeast coast of Vancouver Island, British Columbia. It is located at 48.754286° North and 123.610446° West and is approximately 4 km long and 2 km wide. The mouth of the bay opens into an ocean area between Vancouver Island and mainland Canada known as the Salish Sea, which encompasses the straits of Georgia, Juan de Fuca, and the Puget Sound in Washington (Fig. 2).

The Cowichan River is has the most individual antenna’s (16) and locations (4) on Vancouver Island, allowing for extremely accurate detection efficiency calculations and in-river migration timing and distribution.

Figure 2. The map of Cowichan River PIT antenna sites (orange). This is an interactive map.

PIT tags Deployed in Cowichan River Chinook Salmon

The Bottlenecks Program began in the fall of 2020 and has provided assistance to the ongoing Chinook and coho stock assessment programs being led by Cowichan Tribes, the Department of Fisheries and Oceans and the B.C. Conservation Foundation.

Figure 3. Number of PIT tags deployed in Cowichan River Chinook at each target stage, in each year of the Bottlenecks Study.

Figure 3. Number of PIT tags deployed in Cowichan River Chinook at each target stage, in each year of the Bottlenecks Study.

Cowichan River Tag Detections Through Time

The Cowichan River mainstem PIT array was installed in the summer of 2017 as part of PSF’s Salish Sea Marine Survival Project. The mainstem PIT array is located just upstream of the Highway 19A bridge and is comprised of two transects, with each transect having 6 - 20 ft HDPE PIT antennas; this creates a double-pass array river.

Figure 4. Detections Through Time at the Cowichan River Mainstem Array.

Figure 4. Detections Through Time at the Cowichan River Mainstem Array.

Cowichan River Mainstem PIT Array Detection Efficiency for Adult Chinook Returns

Table 1. Cowichan River Mainstem Array Detection Efficiency for Adult Chinook 2021.
Unique Tags Detected Detection Efficiency
Cowichan River North Arm 0 NaN
Cowichan River South Arm 0 NaN
Cowichan River Mainstem Lower 32 0.56
Cowichan River Mainstem Upper 54 0.94
Skutz Falls 5 0.09
Table 2. Cowichan River Mainstem Array Detection Efficiency for Adult Chinook 2022.
Unique Tags Detected Detection Efficiency
Cowichan River North Arm 50 0.39
Cowichan River South Arm 48 0.36
Cowichan River Mainstem Lower 110 0.80
Cowichan River Mainstem Upper 129 0.90
Skutz Falls 55 0.38
Table 3. Cowichan River Mainstem Array Detection Efficiency for Adult Chinook 2023.
Unique Tags Detected Detection Efficiency
Cowichan River North Arm 45 0.20
Cowichan River South Arm 30 0.15
Cowichan River Mainstem Lower 115 0.60
Cowichan River Mainstem Upper 176 0.87
Skutz Falls 63 0.30
Table 4. Cowichan River Mainstem Array Detection Efficiency for Adult Chinook 2024.
Unique Tags Detected Detection Efficiency
Cowichan River North Arm 105 0.33
Cowichan River South Arm 0 NaN
Cowichan River Mainstem Lower 173 0.65
Cowichan River Mainstem Upper 208 0.76
Skutz Falls 135 0.48

Adult Chinook Returns

The figures in the below section indicate the stock composition of returned PIT-tagged Chinook to the Cowichan River. These data only represent PIT tag data and do not represent the entire stock composition of Fall adult Chinook returns.

The figures below are interactive and moving the cursor over the figure will provide additional information.

Cowichan coho Escapement

Figure 5. Cowichan Chinook Spawn Migration Detections for at the Mainstem Array and Escapement Curves.

Figure 5. Cowichan Chinook Spawn Migration Detections for at the Mainstem Array and Escapement Curves.

Figure 5. Cowichan Chinook Spawn Migration Detections for at the Mainstem Array and Escapement Curves.

Figure 5. Cowichan Chinook Spawn Migration Detections for at the Mainstem Array and Escapement Curves.

Figure 5. Cowichan Chinook Spawn Migration Detections for at the Mainstem Array and Escapement Curves.

Figure 5. Cowichan Chinook Spawn Migration Detections for at the Mainstem Array and Escapement Curves.

Figure 5. Cowichan Chinook Spawn Migration Detections for at the Mainstem Array and Escapement Curves.

Figure 5. Cowichan Chinook Spawn Migration Detections for at the Mainstem Array and Escapement Curves.

Straying in the Cowichan River

Due to the large number of PIT tags being deployed in multiple rivers and salmon updated_stocks along the East Coast of Vancouver Island is the ability to detect straying of other updated_stocks into rivers where PIT arrays are located. Throughout the inaugural four years of the Bottlenecks Study a number of rivers have shown to have other updated_stocks entering and staying in non-natal rivers (Table 5)

Table 5. Non-Cowichan Chinook Detected at the Cowichan River Mainstem Array.
outmigration_y species updated_stock source year_detected tally
2020 ck Nanaimo fall microtroll 2021 1
2020 ck Puntledge fall microtroll 2022 1
2021 ck CHEAKAMUS_RIVER microtroll 2023 1
2021 ck Nanaimo fall hatch_tag 2023 1
2021 ck Nanaimo summer hatch_tag 2023 1
2021 co Englishman river 2021 1
2021 co Puntledge hatch_tag 2021 1
2022 ck Little Qualicum microtroll 2024 1
2022 ck Nanaimo fall hatch_tag 2023 1
2022 ck Nanaimo fall hatch_tag 2024 2
2022 ck Nanaimo fall microtroll 2024 3
2022 co Goldstream hatch_tag 2022 1
2022 co Goldstream hatch_tag 2023 10
2023 co Goldstream hatch_tag 2024 2
2023 co millstone hatch_tag 2020 1
2023 co millstone hatch_tag 2021 1
2023 co millstone hatch_tag 2023 155
2025 co nanaimo hatch_tag 2024 1

PIT tags Deployed in Cowichan River Coho Salmon

Cowichan River Mainstem PIT Array Detection Efficiency for Coho Adult Returns

Table 6. Cowichan River Mainstem Array Detection Efficiency for Adult Coho 2021.
Unique Tags Detected Detection Efficiency
Cowichan River North Arm 0 NaN
Cowichan River South Arm 0 NaN
Cowichan River Mainstem Lower 6 0.71
Cowichan River Mainstem Upper 5 0.57
Skutz Falls 4 0.43
Table 7. Cowichan River Mainstem Array Detection Efficiency for Adult Coho 2022.
Unique Tags Detected Detection Efficiency
Cowichan River North Arm 125 0.41
Cowichan River South Arm 93 0.35
Cowichan River Mainstem Lower 242 0.78
Cowichan River Mainstem Upper 218 0.69
Skutz Falls 175 0.55
Table 8. Cowichan River Mainstem Array Detection Efficiency for Adult Coho 2023.
Unique Tags Detected Detection Efficiency
Cowichan River North Arm 5 0.04
Cowichan River South Arm 26 0.19
Cowichan River Mainstem Lower 41 0.34
Cowichan River Mainstem Upper 85 0.68
Skutz Falls 92 0.72
Table 9. Cowichan River Mainstem Array Detection Efficiency for Adult Coho 2024.
Unique Tags Detected Detection Efficiency
Cowichan River North Arm 11 0.06
Cowichan River South Arm 0 NaN
Cowichan River Mainstem Lower 135 0.81
Cowichan River Mainstem Upper 102 0.61
Skutz Falls 96 0.56

Adult Coho Returns

The figures in the below section indicate the stock composition of returned PIT tagged fish to the Cowichan River. These data only represent PIT tag data from the Bottlenecks to Marine Survival Program and do not represent the entire stock composition of Fall adult Chinook returns.

The figures below are interactive and moving the cursor over the figure will provide additional data fo reach coloured section.

Cowichan River Coho Adult Return Timing

Developing clear return timing graphs, is important in understanding the influences of climate change and how long summer droughts may impact the in-river return timing of fish. Return timing graphs for Cowichan River Coho are presented below.

Cowichan coho Escapement

Figure 1. Cowichan Coho Spawn Migration Detections for 2021 at the Mainstem Array and Escapement Curves.

Figure 1. Cowichan Coho Spawn Migration Detections for 2021 at the Mainstem Array and Escapement Curves.

Figure 1. Cowichan Coho Spawn Migration Detections for 2021 at the Mainstem Array and Escapement Curves.

Figure 1. Cowichan Coho Spawn Migration Detections for 2021 at the Mainstem Array and Escapement Curves.

Figure 1. Cowichan Coho Spawn Migration Detections for 2021 at the Mainstem Array and Escapement Curves.

Figure 1. Cowichan Coho Spawn Migration Detections for 2021 at the Mainstem Array and Escapement Curves.

Figure 1. Cowichan Coho Spawn Migration Detections for 2021 at the Mainstem Array and Escapement Curves.

Figure 1. Cowichan Coho Spawn Migration Detections for 2021 at the Mainstem Array and Escapement Curves.