Dietary analysis of wild and hatchery juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Fraser River estuary reveals differences in ontogenetic shifts
Bibliographic record
Abstract
The Fraser River is the major producer of Pacific salmon (Oncorhynchus spp.) in Canada with millions of juveniles out-migrating through its estuary each year. Estuaries provide critical rearing habitat for juveniles, in particular Chinook salmon (O. tshawytscha), which can reside in estuaries for several weeks. The diet of juvenile Chinook salmon in this habitat is a crucial component of their early development and survival. In 2021 and 2022, I examined size, stomach contents, and stomach fullness of 142 juvenile Chinook salmon of wild and hatchery origin from eelgrass habitat at Roberts Bank (Fraser River estuary). I examined an additional 37 wild Chinook salmon from marsh and sandflat habitats. GSI analyses revealed 83% of all wild fish originated from lower Fraser River populations and PBT analyses revealed 91% of all hatchery fish originated from lower Fraser River populations. In eelgrass habitat, hatchery fish were on average 6.1 mm (~7%) longer than wild fish. Stomach fullness increased with fish size and was ~34% higher in wild fish compared to hatchery fish. Wild fish trended towards fuller stomachs in marsh habitat and emptier stomachs in sandflat habitat compared to those in eelgrass habitat. Stomach content analysis suggested size and time of year were indicators of juvenile Chinook’s transition to a primarily piscivorous diet, which was seen in wild fish with fork lengths as small as 63 mm. Liver and dorsal muscle samples from 130 wild and hatchery Chinook salmon captured in eelgrass habitat were analyzed for δ¹⁵N and δ¹³C revealing overlapping trophic ellipses. Wild fish had greater niche widths compared to hatchery fish and tended to consume higher-quality prey and utilized more diverse habitats compared to hatchery fish highlighting the importance of conserving eelgrass and marsh habitats and the prey they support. To improve foraging competency of hatchery fish in estuaries, naturalization of feeding systems in rearing facilities should be implemented.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 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".