Accuracy and precision of an umbilical-based method for estimating birthdates of pre-weaned harbour seal pups

We evaluated the accuracy and precision of an umbilical-based method for fine-scale age and birthdate estimation in a wild population of harbour seal pups (Phoca vitulina) in the St. Lawrence Estuary, Quebec, Canada. The method consists of attributing umbilicus degeneration scores to estimate pup age in days. To assess its validity, we first constructed a score attribution test with field pictures of pup umbilical cords at various stages of degeneration. This test was completed by 8 observers, and we measured the accuracy and precision of the umbilicus degeneration score attribution. We then used data from 758 pups (captured between 1998 to 2023) for which an umbilical degeneration score was assigned in the field to evaluate the efficiency of this score to estimate birthdate. We show that observers can accurately and precisely attribute umbilicus scores, and that this umbilical-based method can accurately estimate pup birthdates. Here are the two datasets used, as well as a README.md file which describe the data.

Methods
The data was collected by capturing wild habour seal pups in the St. Lawrence Estuary. We used data on the umbilicus degeneration scores in this study, from which we took pictures directly in the field. Those pictures were used to construct the picture test data set.