Dataset for: Estimating pregnancy rate from blubber progesterone levels of a blindly biopsied beluga population poses methodological, analytical and statistical challenges

Beluga (Delphinapterus leucas) from the St. Lawrence Estuary, Canada, have
been declining since the early 2000s, suggesting recruitment issues as a
result of low fecundity, abnormal abortion rates or poor calf or juvenile
survival. Pregnancy is difficult to observe in cetaceans, making the
ground-truthing of pregnancy estimates in wild individuals challenging.
Blubber progesterone concentrations were contrasted among 62 SLE beluga
with a known reproductive state (i.e., pregnant, resting, parturient, and
lactating females), that were found dead in 1997–2019. The suitability of
a threshold obtained from decaying carcasses to assess reproductive state
and pregnancy rate of freshly-dead or free-ranging and blindly-sampled
beluga was examined using three statistical approaches and two datasets
(135 freshly-harvested carcasses in Nunavik, and 65 biopsy-sampled SLE
beluga). Progesterone concentrations in decaying carcasses were
considerably higher in known-pregnant (mean ± sd: 365 ± 244 ng g-1 of
tissue) than resting (3.1 ± 4.5 ng g-1 of tissue) or lactating (38.4 ± 100
ng g-1 of tissue) females. An approach based on statistical mixtures of
distributions and a logistic regression was compared to the commonly-used,
fixed threshold approach (here, 100 ng g-1) for discriminating pregnant
from non-pregnant females. The error rate for classifying individuals of
known reproductive status was the lowest for the fixed threshold and
logistic regression approaches, but the mixture approach required limited
a priori knowledge for clustering individuals of unknown pregnancy status.
Mismatches in assignations occurred at lipid content <10% of sample
weight. Our results emphasize the importance of reporting lipid contents
and progesterone concentrations in both units (ng g-1 of tissue and ng g-1
of lipid) when sample mass is low. By highlighting ways to circumvent
potential biases in field sampling associated with capturability of
different segments of a population, this study also enhances the
usefulness of the technique for estimating pregnancy rate of free-ranging
population.

加拿大圣劳伦斯河口（St. Lawrence Estuary，下文简称SLE）的白鲸（Delphinapterus leucas）种群自21世纪初以来持续衰退，推测其原因为繁殖力低下、异常流产率偏高，抑或是幼崽及亚成体存活率不足所引发的种群补充问题。
由于鲸目动物的妊娠状态难以直接观测，对野生个体妊娠评估结果进行实地验证颇具挑战。
本研究对1997至2019年间搁浅死亡的62头已知繁殖状态（妊娠、静息、产仔及泌乳雌性）的SLE白鲸的鲸脂（blubber）孕酮浓度开展了对比分析。
本研究采用三种统计方法与两套数据集，评估了利用腐烂鲸尸得到的孕酮阈值，判断新近死亡个体、自由栖息的野生个体及盲采样白鲸的繁殖状态与妊娠率的适用性：两套数据集分别为努纳维克地区135头新近死亡的鲸尸，以及65头经活检采样的SLE白鲸。
已知妊娠个体腐烂鲸尸中的孕酮浓度（平均值±标准差：365±244 ng·g⁻¹组织）显著高于静息个体（3.1±4.5 ng·g⁻¹组织）与泌乳个体（38.4±100 ng·g⁻¹组织）。
本研究将基于分布混合模型与逻辑回归的分析方法，与常用于区分妊娠与非妊娠雌性的固定阈值法（本次研究中阈值设为100 ng·g⁻¹）进行了对比。
在对已知繁殖状态个体的分类任务中，固定阈值法与逻辑回归法的错误率最低，但分布混合模型法仅需有限的先验知识即可对未知妊娠状态的个体完成聚类。
当样本脂质含量低于样本总重的10%时，个体分类结果会出现匹配偏差。
本研究结果强调，在样本重量较低时，需同时报告以组织重量（ng·g⁻¹ tissue）和脂质重量（ng·g⁻¹ lipid）为单位的孕酮浓度与脂质含量。
本研究还针对因种群不同群体的可捕获性所引发的野外采样偏差问题提出了规避路径，从而提升了该技术在估算自由栖息野生种群妊娠率方面的应用价值。