Age determination of mysticete whales using<sup>210</sup>Pb/<sup>226</sup>Ra disequilibria
Bibliographic record
Abstract
Accurate age determination is fundamental to the study of population structure and individual growth rates of mysticete whales. Here the disequilibrium between210Pb and226Ra in the tympanic bullae of two mysticete whale species was investigated for use as a chronometer. Radiometric ageing depends upon accumulation of the naturally occurring radionuclide226Ra (exclusive of other238U decay-chain members) in the bullae and subsequent retention of its progeny210Pb. Ages are determined from the210Pb/226Ra activity ratio. Samples were obtained from five gray whales (Eschrichtius robustus) with lengths of 4.5 (a neonate), 7.8, 8.7, 10, and 11.5 m, and two bowhead whales (Balaena mysticetus) with lengths of 12.9 and 17.4 m. In gray whales, radiometric ages were estimated in the three largest whales. In the neonate, the210Pb/226Ra ratio was above one and was not usable. The 7.8-m gray whale was used to determine the initial210Pb/226Ra ratio required for age determination. We propose a theory of gray whale bullae growth starting at the fetal stage with an open system (with a210Pb/226Ra > 1 and a fast growth rate), which transitions by 1 year old to a closed system (with a210Pb/226Ra << 1 and a slow growth rate). In both bowhead whales, radiometric age could not be estimated because the210Pb/226Ra ratio was above one. The excess210Pb in these bullae samples was likely accumulated from the whales' environment via prey, or in the case of the neonate gray whale, across the placental boundary. Our results indicate that the underlying assumptions of the210Pb/226Ra radiometric ageing method may not hold true in bowhead whales. Successful application of this method to bowhead whales is therefore doubtful.
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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 | 0.000 |
| 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".