Renaud L-A, Bordeleau X, Kellar N M, Pigeon G, Michaud R, Morin Y, Lair S, Therien A, Lesage V
Department of Fisheries and Oceans Canada, Maurice Lamontagne Institute, P.O. Box 1000, 850 Route de la Mer, Mont-Joli, Québec, G5H 3Z4, Canada.
Southwest Fisheries Science Center, National Marine Fisheries Service, P.O. Box 271, La Jolla, California 92038, USA.
Conserv Physiol. 2023 Sep 26;11(1):coad075. doi: 10.1093/conphys/coad075. eCollection 2023.
Beluga () 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 to 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 data sets (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 of tissue) than resting (3.1 ± 4.5 ng g of tissue) or lactating (38.4 ± 100 ng g of tissue) females. An approach based on statistical mixtures of distributions and a logistic regression were compared to the commonly-used, fixed threshold approach (here, 100 ng g) 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 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 of tissue and ng g 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的白鲸自21世纪初以来数量一直在减少，这表明繁殖问题是由于繁殖力低、异常流产率高或幼鲸或幼体存活率低造成的。鲸类动物的怀孕情况很难观察到，这使得对野生个体怀孕估计进行实地核实具有挑战性。对1997年至2019年间死亡的62头已知繁殖状态（即怀孕、休息、分娩和哺乳的雌性）的圣劳伦斯河口白鲸的鲸脂孕酮浓度进行了对比。使用三种统计方法和两个数据集（努纳维克的135头新捕获的尸体，以及65头经活检取样的圣劳伦斯河口白鲸），检验了从腐烂尸体获得的阈值用于评估新死亡或自由放养且盲目取样的白鲸的繁殖状态和怀孕率的适用性。已知怀孕的雌性（平均±标准差：365±244纳克/克组织）的腐烂尸体中的孕酮浓度明显高于休息的雌性（3.1±4.5纳克/克组织）或哺乳的雌性（38.4±100纳克/克组织）。将基于分布统计混合的方法和逻辑回归方法与常用的固定阈值方法（此处为100纳克/克）进行比较，以区分怀孕和未怀孕的雌性。对于已知繁殖状态个体的分类，固定阈值和逻辑回归方法的错误率最低，但混合方法在对未知怀孕状态个体进行聚类时所需的知识有限。在脂质含量低于样品重量的10%时，分类出现不匹配。我们的结果强调了在样品质量较低时，以两种单位（纳克/克组织和纳克/克脂质）报告脂质含量和孕酮浓度的重要性。通过强调规避与种群不同部分的可捕获性相关的野外采样潜在偏差的方法，本研究还提高了该技术在估计自由放种群怀孕率方面的实用性。
