Effects of release size, location, and timing on the freshwater residence and early survival of Chinook salmon (Oncorhynchus tshawytcha) on the west coast of Vancouver Island
Bibliographic record
Abstract
Hatchery enhancement of declining Pacific salmon populations has long been a foundation of salmon management; however, the influence of hatchery release practices on freshwater residence time and survival to estuarine entry is not well-understood. This study employed Passive Integrated Transponder (PIT) tags to evaluate the relationships between the size of individuals at release, release location, and release timing on the duration of freshwater residence and survival of hatchery-produced Chinook salmon (Oncorhynchus tshawytscha) in the 103 km2 Toquaht River watershed, located on the west coast of Vancouver Island, British Columbia. The Toquaht River mainstem is ~22 km in length, divided into upper and lower sections by the 118 ha Toquaht Lake. A total of 4848 PIT-tagged Chinook salmon smolts were released on three dates (May 23rd, June 9th, June 19th), and during each release, fish were split evenly between three different locations within the watershed (Toquaht Lake: 7.9 km from the detection array; upper river: 11.9 km from the array; and the lower river: 4.1 km from the array). The detection data were analyzed using an integrated model of freshwater residence and capture–recapture fitted using Bayesian inference. The duration of freshwater residence between release and detection ranged from 0.5–60 days, with a mean of 14 days, and exhibited a negative relationship with fish size. The estimated median survival probability for all locations and dates was 0.39, with the highest probability of survival (0.78) found in fish released into the lake on June 19th and the lowest (0.06) for lower-river fish released on June 9th. Changes in streamflow were likely responsible for the observed pattern in survival by date. Survival probability decreased as fish size increased. Overall, the study provides further evidence that hatchery release strategies can significantly influence freshwater residence and survival, and these practices should be well-understood and flexible in the face of changing environmental conditions. The results of this study may have significant implications for the management of Toquaht River Chinook salmon, particularly in the context of ongoing efforts to rebuild the naturally spawning population.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".