Bottlenecks Program Coastal Cutthroat Trout Movement

The Bottlenecks Program was initiated in 2020 to conduct a large expansion of PIT tag infrastructure along the East Coast of Vancouver Island. The primary objective was to develop stage specific survival estimates for Chinook and coho, and marine survival estimates for a hatchery steelhead population (Robertson Creek) and two wild populations (Cowichan and Quinsam rivers). Methods of capture for targetting wild Chinook, coho and steelhead also work well for capturing migrating Coastal Cutthroat Trout (via in-river smolt traps, wolf traps, and beach seining in estuaries). Due to the captures of these non-target species, the Bottlenecks Program began opportunistically tagging Coastal Cutthroat Trout at primary study systems (Cowichan, Nanaimo and Puntledge rivers), and at wild coho tagging rivers (Englishman River).

The deployment of PIT tags across multiple rivers and years is the first study of this magnitude to assess migrations and marine survival of Coastal Cutthroat Trout (James Losee, Wild Salmon Center. pers. comm. 2024).

Table 1. Bottlenecks Program PIT Tagged Coastal Cutthroat Trout All Systems.
Watershed River Year 1 Year 2 Year 3 Year 4
black creek black creek 3 0 0 0
cowichan cowichan 14 13 11 44
englishman center creek 21 72 98 219
englishman shelly creek 49 5 16 25
englishman side channel 0 2 0 12
nanaimo nanaimo 24 0 6 27
puntledge puntledge 8 82 43 52

Englishman (Kw’a’luxw) River

The Bottlenecks Program has been tagging Coastal Cutthroat Trout on Kw’a’luxw River since the spring of 2021. Smolt traps are deployed in Center and Shelly creeks during the coho outmigration; to capture and tag outmigrating coho for marine survival estimates.

Englishman (Kw’a’luxw) River Coastal Cutthroat Trout

Figure 1. PIT Tagged Coastal Cutthroat Trout Fork Length Density Plots for Englishman River

Figure 1. PIT Tagged Coastal Cutthroat Trout Fork Length Density Plots for Englishman River

Center Creek Coastal Cutthroat Trout

Figure 2. PIT Tagged Coastal Cutthroat Trout Fork Length Density Plots for Centre Creek

Figure 2. PIT Tagged Coastal Cutthroat Trout Fork Length Density Plots for Centre Creek

Figure 3. Coastal Cutthroat Trout Detections on Englishman Mainstem Array at Plummer Road

Figure 3. Coastal Cutthroat Trout Detections on Englishman Mainstem Array at Plummer Road

Figure 4. Coastal Cutthroat Trout Age Class at Time of Tagging. Age Class was derived from Atkinson, Anderson and Losee 2025.

Figure 4. Coastal Cutthroat Trout Age Class at Time of Tagging. Age Class was derived from Atkinson, Anderson and Losee 2025.

Table 2. Coastal Cutthroat Trout Recapture Proportions by River and Year for the Englishman River.
River Year Total Deployed Same Year Recaptures Any Year Recaptures Percent Anadromy (%)
center creek 2022 72 13 4 23.6
center creek 2023 98 43 2 45.9
center creek 2024 219 80 0 36.5
shelly creek 2022 5 3 0 60.0
shelly creek 2023 16 4 0 25.0
shelly creek 2024 25 9 0 36.0
side channel 2022 2 0 1 50.0
side channel 2024 12 1 0 8.3

Coastal Cutthroat Trout Straying

There have been few documented observations of Coastal Cutthroat Trout straying outside of their natal systems (James Losee, Wild Salmon Center. pers. comm. 2024). Further, while there have been observations of straying in Coastal Cutthroat Trout these have been limited to relatively close systems (~10 km) and have comprised an extremely small percentage of tagged fish within given studies. The Bottlenecks Program has detected a total of four Coastal Cutthroat Trout strays across the Program. Interestingly, these individuals migrated > 40 km in each case; with some Coastal Cutthroat Trout being detected a few kilometers (~3 km) upstream of tide water.

Table 3. Coastal Cutthroat Trout Straying by Year and Watershed.
Natal Watershed Year Strayed To Total Straying Total Deployed Percent Straying (%)
englishman 2023 nanaimo 1 114 0.9
englishman 2024 little_qualicum 1 256 0.4
puntledge 2023 black_creek 1 43 2.3
puntledge 2024 big_qualicum 1 52 1.9

Bottlenecks Program PIT Tagged steelhead and Rainbow Trout

Table 4. Bottlenecks Program PIT Tagged steelhead All Systems
Watershed River species 2021 2022 2023 2024
cowichan cowichan stl 409 85 66 160
englishman center creek stl 17 2 28 28
nanaimo nanaimo stl 35 0 4 52
puntledge puntledge stl 10 2 0 1
quinsam quinsam stl 479 338 130 237
englishman shelly creek stl 0 0 0 14
englishman side channel stl 0 0 0 12
Table 5. Bottlenecks Program PIT Tagged Rainbow Trout All Systems
Watershed River species 2021 2022 2023 2024
cowichan cowichan rbt 39 8 27 128
englishman center creek rbt 91 72 46 80
englishman shelly creek rbt 29 28 12 24
englishman side channel rbt 1 1 2 12
nanaimo nanaimo rbt 49 3 30 105
puntledge puntledge rbt 9 4 0 0
koksilah koksilah rbt 0 31 408 0
chemainus chemainus rbt 0 0 14 0
koksilah kelvin rbt 0 0 39 0