Using otoliths to determine daily growth rate and size-selective mortality of juvenile salmon in Nanaimo, British Columbia
Bibliographic record
Abstract
Available evidence suggests that interannual variability in the recruitment of Pacific salmon is related to survival in the first few months juveniles spend at sea. Differential growth of smolts during this stage is often thought to result in interannual differences in marine survival, as those fish that grow faster may be less vulnerable to predators or physiological and environmental stressors associated with overwintering (i.e. the 'differential growth' hypothesis). Due to the limitations of traditional techniques, however, only rarely has salmon growth been reliably characterized during the early marine stage. Using juvenile chum salmon (Oncorhynchus keta) collected in the Nanaimo area (1999-2001), I demonstrate that otoliths provide a powerful means of examining the early life history of individual salmon in the field. I used a fluorescent marker to validate the daily periodicity of otolith increment formation, and the formation of a marine entry check. I then back-calculated size-atmarine- entry for each chum smolt to provide individual estimates of early marine growth rate from the summers of 1999 and 2000. Mean daily growth rates were significantly higher, and size-at-entry significantly larger, in 1999 (0.084 cm day"1, 4.48 cm) than in 2000 (0.076 cm day"1, 3.97 cm). 1999 was also a year of significantly higher gut fullness and lower sea surface temperatures. By comparing growth rate frequencies across trips, I found evidence for size-selective mortality of slow growing fish in the midsummer of 2000. These patterns are consistent with the "differential growth hypothesis". In years of unfavourable ocean conditions, juvenile salmon may experience slower growth and higher rates of size-selective predation (possibly due to low food availability or quality). This, in turn, may lead to below average survival and recruitment in these years.
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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 | 0.001 | 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".