Hatchery Chinook Salmon straying in Southern BC
Bibliographic record
Abstract
Hatchery-origin salmon provide significant socio-economic benefit as well as conservation value in some cases, but high levels of hatchery production can create fishery, ecological, and genetic risks for natural populations. The risks of hatchery-origin Chinook straying into non-natal rivers was the focus of this assessment. Straying was described from two distinct perspectives: from the populations in which strays originate, i.e., donor populations, and from the populations that receive them, i.e., recipient populations. This report describes first generation, hatchery-origin straying of 19 ocean-type populations and one stream-type Chinook Salmon population into non-natal rivers in Southern British Columbia using Coded Wire Tag (CWT) and otolith thermal mark data. Based on in-river samples, average hatchery donor stray rates were estimated at approximately 4% based on otolith thermal marks and 2% based on CWT samples. The donor stray rate to non-natal Conservation Units (CUs) was lower—less than 2% across populations and years—and was negligible between Stock Management Units (SMU). Lower stray rates from large hatchery releases can still result in a large magnitude of strays observed in smaller non-natal systems. Conuma Hatchery on the West Coast of Vancouver Island (WCVI) had a substantially higher donor stray rate; the highest among large-scale production hatcheries, which resulted in the greatest magnitude of strays to other rivers. Local and regional variability in environmental factors made separating their causal effect on stray rate from hatchery practices difficult. While the influence of hatchery practices from potential environmental factors were not statistically delineated in this work, the need for hatcheries to prioritize imprinting to reduce stray rates was emphasized. The contribution of strayed, hatchery-origin spawners (pHOSstray) in the escapement was identified as a metric to assess the impact of strays on natural-origin populations; observed values were compared to a 0.03 benchmark established for wild populations. Average pHOSstray was highest on the WCVI with most strays originating from Conuma Hatchery. Lower values, mostly below the 0.03 benchmark were observed on the East Coast of Vancouver Island (ECVI), and a negligible hatchery stray contribution was observed in Fraser River populations. Proportionate natural influence (PNI) is a metric used to evaluate and monitor the level of natural influence and genetic risk in integrated populations. On the WCVI, particularly in northern populations, PNI was low; ECVI had more populations with moderate to high PNI values; and the Fraser River contained many populations with consistently high PNIs. Genetic analysis indicated that genetic variation remained consistent for the three major hatchery populations within the WCVI from 1985–2015. On the WCVI, genetic results indicated that hatchery populations contributed significantly to natural spawners and resulted in increased genetic homogenization among non-natal rivers. The persistence of natal genetic signals in WCVI rivers that have experienced some level of homogenization suggests that enhanced contribution management, using PNI, is important to preserve wild influence and associated genetic diversity. Withler et al. (2018) and US Hatchery Scientific Review Group (HSRG; 2009) publications indicated a need for the adaptive and scientifically defensible management of hatcheries. The results presented in this report support this view, and suggest that the inclusion of a stray management framework would support these principles.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".