Designing a Measurement Methodology for the Upper Aerodigestive Tract of Phoca vitulina

Abstract

In North America, wild harbor seal neonates and pups (Phoca vitulina) are among the most common marine mammals admitted to rescue centers. Nutritional support is typically via gavage as most are admitted prior to weaning. In order to advance seal feeding and swallowing rehabilitation, we require a comprehensive understanding of their upper aerodigestive tract (UAT) as it applies to swallowing physiology. Anatomical studies of the harbor seal UAT are limited, and standardized UAT measurements for neonates and pups have not yet been determined. Our objective is to design a systematic method to measure their UAT structures and then obtain quantitative values. During post mortem examination, we photographed UAT structures using scalars. Structures included: tongue, vocal folds, cricoid cartilage, trachea, and epiglottis. A priori, we developed a manual outlining measurement start and endpoints using ImageJ (NIH, 2010). Following measurements, we summarized results with means (standard deviations, [SD]) and medians (interquartile ranges, [IQR]) as appropriate and explored correlations (Pearson’s correlation coefficient, one‐tailed) between UAT structures and other body measurements. We used IBM SPSS analytical software version 26 (IBM Corporation, 2019) for analyses with significance of p<.05. Our specimens included 14 deceased harbor seal neonates or pups (9 males, 5 females) aged between three days and 2 months old at the time of death. Causes of death were either: spontaneous, congenital, or due to infectious, metabolic or malnutrition disorders, or by euthanasia after a humane endpoint was reached. On admission to rehabilitation, body measurement ranges included: 46.0 to 57.0 (body length [cm]), 36.0 to 59.0 (axillary girth [cm]) 5.8 to 12.6 (weight [kg]). Post‐mortem UAT measurements (mm, mean ± SD) included: 1) tongue tip to epiglottis base: 82.7 ± 6.9, 2) vocal fold length: 13.9 ± 2.0, 3) tracheal diameter: 10.3 ± 1.4, and 4) epiglottic length: 20.0 ± 2.8. Correlations between seal body length and UAT dimensions were not statistically significant. In conclusion, we have developed a systematic method to measure harbor seal neonate and pup UAT structures. To the best of our knowledge, these measurements, as they relate to swallowing, have not been previously reported. These findings expand the seal macroscopic anatomy knowledge base and contribute to cross‐species conceptual convergences between human and seal swallowing physiology and its rehabilitation.Support or Funding InformationSupported by a UBC Faculty of Medicine Summer Student Research Program 2019 award to Hirad Nourbakhsh, UBC Faculty of Medicine Start‐up grant to Stacey A. Skoretz and by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to A. Wayne Vogl (RGPIN‐2018‐03727).