Seaward movements of Keogh River steelhead parr : density-dependent dispersal and premature migration
Bibliographic record
Abstract
Steelhead (Oncorhynchus mykiss) parr captured at a full stream enumeration trap at the mouth of the Keogh River, northern Vancouver Island, British Columbia comprised 9-35% (mean = 20%) of seaward dispersing juvenile (smolts + parr) steelhead, 1977-1993. Total parr annually varied from 400-5000 (mean = 1600). I tested two competing hypotheses to explain this biologically significant phenomenon: parr seaward movement is (1) premature but directed migration homologous to smolt migration, and (2) downstream dispersal resulting from upstream, density-dependent interactions among juvenile steelhead. At the watershed scale, reconstruction of past stream population sizes of steelhead juveniles suggested exponentially increasing parr dispersal as estimated main stem population size increased. At the reach scale, steelhead parr dispersed from experimentally stocked reaches; high initial stocking densities revealed limits to reach carrying capacity. At the individual trout scale, observations of agonistic behaviour of non-dispersing and dispersing parr in artificial stream channels showed that parr size was more important than parr type in determining attack rate. Dispersing parr had both growth rates and body shape (indexed by condition factor) that were intermediate between smolts and non-dispersing parr of the same age. Finally, parr dispersal followed the same seasonal timing pattern that smolt migration followed in 14 years of daily downstream movement data. Experimental manipulation and observation of naturally occurring patterns produced data supporting each hypothesis. Therefore, parr seaward movement in the spring at the Keogh River seems to be a phenomenon blended from indirect density-dependent effects as well as premature migration.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| 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".