Abstract: 

Accurate inference of sexual maturity is fundamental to interpreting marine mammal life histories and population structure. Using Bayesian logistic regression models with a hierarchical ordinal (HOF-style) parameterisation and canonical analysis of principal coordinates (CAP), we evaluate skeletal metrics in the pectoral flippers of common dolphin (Delphinus delphis) as indicators of attainment of sexual maturity. HOF models were used to relate sexual maturity to skeletal ossification, generating probabilistic response curves based on (i) a total bone score defined as the sum of discrete morphological maturation stages (scored from −1 to 8) across 16 flipper bones, and (ii) the minimum maturation stage (−1 to 8) reached by either the distal radius or ulna. For total bone scores, the predicted midpoint of sexual maturity (probability = 0.5) occurred at an ossification score of 74.85 points in females (95% credible interval: 72.50–77.13) and 68.35 points in males (95% credible interval: 63.47–73.12), with a steeper transition in females. For the minimum radius–ulna score, midpoints were similar between sexes, at 4.90 in females (95% CI: 4.51–5.27) and 4.75 in males (95% CI: 4.32–5.16). CAP was applied as a complementary multivariate constrained ordination method to distinguish immature and mature individuals based on combined ossification patterns and to quantify leave-one-out classification performance. For the whole dataset, CAP demonstrated strong discrimination between maturity states (squared canonical correlation = 0.84), with 95.8% of females and 98.4% of males correctly classified and misclassification restricted to individuals near the maturity boundary. Together, these results demonstrate that radiographic skeletal ossification provides a robust proxy for sexual maturity in common dolphins in New Zealand.

Kind regards,

Evi Hanninger​​