Development of predictive models for determining fetal age‐at‐length in belugas (Delphinapterus leucas) and their application towardin situandex situpopulation management

Abstract

AbstractFor wild belugas (Delphinapterus leucas), gestation length estimates based on fetal size have produced extreme ranges.Ex situpopulations thereby provide unique opportunities to define this important life history event. Accordingly, research with ultrasound was conducted on six beluga whales over 11 gestations with known conception dates to serially measure fetal changes in biparietal diameter (BP), thoracic diameter (TD), thoracic circumference (TC), and total length (TL). Incremental polynomial regression analyses were performed on each fetal measurement to develop predictive models for determining age based on fetal size and days from parturition. Gestation length (n= 11) was a mean 467 ± 5.4 d with male calves (478 ± 8.6 d) experiencing a longer gestation (P= 0.04) than females (457 ± 3.9 d). Age atTLwas best described using a 2nd order polynomial model, while linear relationships existed forBPD,TD, andTC. Accuracy was improved for predicting age (P= 0.001) or days prior to parturition (P= 0.038) using data from the firstvs. the second half of gestation. The results provide accurate models for aging beluga fetuses based on size in bothin situandex situpopulations.